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[email protected]#$ing an 86 LG4 Quadrajet

Old 11-11-2018, 01:14 AM
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[email protected]#$ing an 86 LG4 Quadrajet

I just bought a 1986 Camaro with the LG4 V8 and 5-speed. It runs, but not very well. And unfortunately one or more of the POs have ripped out most of the emissions equipment, and left a bunch of open vacuum leaks on the carb.

I'm trying to sort out which port is for what, and figure out which emissions parts I can live without for now, and which are critical.

I've done some research and found this great link on how the system works. It's pretty clever, and as a former mechanical engineer I love learning about stuff like this. But most of my life I have designed or worked on electronic fuel injection, or mechanical fuel injection. My carb knowledge is limited, and my electronic carb knowledge was nil before buying this Camaro.

So first stupid question... are the vacuum ports labelled on the carb? I still have the vacuum diagram under the hood, I'm just missing most of the parts.




Is this the Vacuum Sensor that should be plugged into port N on the back of the carb? (the vacuum line isn't currently connected)



Is this the barometric pressure sensor? The wiring colors don't match the wiring diagram, but it's close.



Which port do I plug the air cleaner vacuum line into? There is one just above the fuel line on the front of the carb, and one below it. The one below it I have capped off in this photo. There is also a massive vacuum port on the front of the carb, I believe this goes to the purge canister?



I'm going to hit my local Pick N Pull and see if I can find some of this missing emissions stuff. I don't plan on putting the air pump back on, but I'd like to get all the carb functions working properly, get the EGR working, and the purge canister. I don't see the point in deleting that.

Thanks for any help you can provide this noob, lord knows I'm going to need it!

Ian
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Old 11-11-2018, 02:20 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

You are doing fine so far. To answer your questions
VAC sensor - yes.
BARO - yes.
Air cleaner vac line - above.
Purge canister port - yes.

The letters on the diagram are on the carb itself. Look closely, they are raised letters.

Any check engine lights? Does the carb make a ticking sound with key ON, engine OFF?
What are the emissions requirements in your state?
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Old 11-11-2018, 02:29 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Sweet! Thanks for the reply.

Yes it makes a ticking noise. What is that?

In my area (Portland Oregon) we do have emissions testing. But I thinks it’s just a sniff test in the exhaust, not a visual under the hood. So I can probably live without the air injection.

worst case I can register it as an antinque and avoid smog. But for now I just want to get it running well.

Thanks again!
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Old 11-11-2018, 09:07 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

the computer controlled carb has a mixture control solenoid inside that cycles at 10 HZ. this solenoid forces two tapered primary rods down into the primary jets that restrict fuel flow based on the computer commanded dwell of the solenoid. when the rods are down, fuel is restricted and the mixture leans. the computer has a default program of dwell settings based on load, rpm and throttle opening as read by the vac, throttle position sensor and distributor. the program blocks are constantly re-written based on readings from the O2 sensor (within the limits of the computer). the baro sensor will make some corrections based on atmospheric pressure and the coolant temp sensor will provide some enrichment until the engine is at operating temp.

the ecm controls timing advance of the distributor and will retard timing based on information from the knock sensor. the ecm also commands lock up for the torque converter based on speed and throttle position and will engage the idle bump solenoid (raise the curb idle speed) under certain deceleration conditions. it will also command the EGR and AIR system functions. the 87 LG4 also had a computer conrolled solenoid for the purge, but pretty sure you won't have that on an 86.

the primary adjustment for the ccc-qjet is the dwell. the dwell can be read from a diagnostic lead near the ecm harness entrance by the blower motor. it is set to near 50% at warm idle by adjusting the Idle Air Bleed screw center top of the carb. this is done to provide the ecm the best range of control over dwell, rich and lean.

your carb looks to have never been opened, the factory cover over the IAB appears intact. i would verify that the dwell is proper and varying as it should along with proper TPS setting (the TPS is a common fail point). that function check along with getting a little better than 20 miles per gallon would tell me to leave the carb alone for now. otherwise we can help with a rebuild if necessary.

first thing I would do though is a full tune up, which would include replacing all plugs, wires, the cap and rotor if any are of unknown condition or age.
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Old 11-11-2018, 10:25 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Originally Posted by Alfisti View Post

So first stupid question... are the vacuum ports labelled on the carb? I still have the vacuum diagram under the hood

Ian
Here's A Pic Showing The Marked Ports.


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Old 11-11-2018, 10:33 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Thank you guys!

I made a bit more progress today. I plugged in the vacuum sensor on the driver side and checked the rest of the ports.

The EGR solenoid was plugged into B, so I moved it down to J. B is now capped off waiting for a vacuum line to the air cleaner temp sensor.

The PCV is plugged into L with a T, the smaller part of the T is capped as I believe it is supposed to go to to the EFE TVS and the air mgmt valve.

T is also capped and so is H.

But there is a line coming out of K I think that goes around to the back of the engine and plugs into something on the manifold. See photo below:



That line is plugged into the front of the carb, between the black cap and the TPS below.


Other questions:

Does the hose coming off the barometric pressure sensor connect to anything? It doesn't look like it was connected to anything.



I also need to figure out how to attach a tachometer so I can see how high it's idling. It doesn't want to kick down, if I have anything else connected incorrectly hopefully I can sort it out soon.

I do have a dwell meter so I can test that once I get the vacuum lines sorted.

I also found the braided ground strap between the engine and the firewall is broken, so I plan to reattach that.

Thanks again!

Last edited by Alfisti; 11-11-2018 at 10:42 PM.
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Old 11-12-2018, 08:33 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

the vacuum source on the manifold, rear of carb provides accessory vacuum. it should be connected to a line that runs to the vacuum reservoir under the left side 'batt' tray and go into the HVAC harness. without that vacuum source connected the interior vents will not switch from defrost to any other setting.

the front port on the carb where that line is connected should provide vacuum to your canister control valve, which appears to be missing. this valve opens the port to the evap canister to purge it of fumes under certain engine temp and vacuum conditions.

the baro sensor should not be connected to a vacuum source, else it would not read atmospheric pressure.
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Old 11-12-2018, 11:35 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Originally Posted by naf View Post
the vacuum source on the manifold, rear of carb provides accessory vacuum. it should be connected to a line that runs to the vacuum reservoir under the left side 'batt' tray and go into the HVAC harness. without that vacuum source connected the interior vents will not switch from defrost to any other setting.

the front port on the carb where that line is connected should provide vacuum to your canister control valve, which appears to be missing. this valve opens the port to the evap canister to purge it of fumes under certain engine temp and vacuum conditions.

the baro sensor should not be connected to a vacuum source, else it would not read atmospheric pressure.

Thanks again NAF! I will move that HVAC vacuum line and plug the port on the carb and try again. I also read to check the PCV valve and see if it is sticking open.

I think the HVAC vacuum reservoir is up by the brake booster on this car, I found a line off it going into the firewall and saw a photo of it in another thread.

I will leave the baro sensor, I'm not sure why it has. Hose on it but it shouldnt matter as long as the hose is free.

I will let you know the latest results

Ian
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Old 11-12-2018, 12:30 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Following along......
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Old 11-12-2018, 03:56 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

earlier cars had the vacuum reservoir cylinder near the brake booster, surprised your's is there.

if you have cruise control, that system also receives it's vacuum source from the port on the manifold.

the vacuum for the brake booster goes to the threaded hard fitting on the rear of the carb base.

the baro sensor is visually identical to the vac sensor. I've seen different part numbers for them but they operate identically, obviously. the diaphragm for the sensor is just exposed to atmospheric pressure on the baro vs vacuum on the vac sensor. there is likely only a small difference internally. You can remove the hose.

if the little ball inside the PCV valve rattles, it's probably fine. a new one is fairly inexpensive though.
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Old 11-12-2018, 04:04 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

another tip

unless you live where it gets cold and have to drive this car in those conditions, you can remove the EFE system. it is designed to divert exhaust gases back through intake manifold passages to speed warm up. It does this by closing a butterfly valve in the passenger side exhaust. the valve is between the manifold and y-pipe. the butterfly valve (EFE valve) can be left in place.

although your TVS for this system on the waterneck looks intact. it may not be worth the effort to plumb it back up. the system should have a flexible vacuum line connected to a hard metal line that runs along the VC and down to the valve. there a short section of vacuum line connects the hard line to the valve. the short section is most probably crumbled to dust by now.

this system can be re-built, but I'd put it on the back burner for now.
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Old 11-12-2018, 04:08 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

looking at your photos I see two ground leads that are attached to the rear mounting bolt for the carburetor.

they should be attached to the rear of the cylinder head which would be a much better ground (they're for the ECM harness).
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Old 11-12-2018, 06:14 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

OK latest update.

I moved the HVAC vacuum line and plugged the port on the carb. I also checked the PCV valve and if you shake it it Rattles, so I think it's OK.

I also disconnected the EGR valve and plugged the port with no change.

The car starts easily but still idles high. I need to find a better tachometer so I can measure it.

I let it warm up and tried to kick it down with no luck. So if it doesn't have any vacuum leaks I'm thinking it might be time to try adjusting the idle settings. But before I do are there any simple checks to make for sticky or binding linkages? I did pull the throttle cable off to make sure it wasn't holding it open, and it's not.

Any other suggestions?
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Old 11-12-2018, 06:37 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Originally Posted by naf View Post
looking at your photos I see two ground leads that are attached to the rear mounting bolt for the carburetor.

they should be attached to the rear of the cylinder head which would be a much better ground (they're for the ECM harness).
I thought those were supposed to be attached to the cylinder head. Isn't there supposed to be a bolt right below the valve cover on the back of the head? I can feel a hole there, I assume the bolt is lost. But I will grab one and move the grounds. I did reattach the braided ground to that cluster, but I will move it.

Thanks for the tip on the EFE system too. Someone replaced the valve covers with chrome versions and if there were hard lines on the valve covers they are gone. It doesn't get that cold in Portland and I'm not using it for commuting so I can just leave that plugged off for now.

​​​
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Old 11-13-2018, 12:41 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

So my plan tomorrow is to use a little carb cleaner to look for any vacuum leaks. Then check the fast idle cam and see if it's sticking, and also to check the fast idle and warm idle stops.
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Old 11-13-2018, 08:01 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

determine whether the idle is being held high by the curb idle speed or the fast idle cam for the choke.

when the choke is cold, the coil spring inside will close the choke and a cam will swing around and hold the primary throttle open slightly higher than the curb idle setting. when the choke opens completely, gravity will pull this cam out of the way and allow the throttle to close to the curb idle screw. it's all under and around the choke coil but if you examine it closely and play with it some, you can see how it's supposed to work. carb cleaner and some light oil can help clear up some of the linkage, most of the shafts are Teflon coated, which wears off with time.

Note that a closed choke prevents the secondaries from opening. The choke pulloff cracks the choke open slightly once it gets a vacuum signal, providing an easier start for the engine with the choke completely closed. it also provides some delay in opening the secondaries along with the air valve spring and set screw.
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Old 11-13-2018, 06:25 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Well I determined that the choke isn't working. It never closes. I have 12V at the connector, but the connector is broken. So I had it zip tied on but it just isn't closing.

If I push down on the cam the idle drops, but of course as soon as I blip the throttle it pops up again and the idle climbs.

I ordered a new choke thermostat which will take a few days to get here, so I'm going to work on tidying a few other things.

I also checked for codes after replacing the burned out Check Engine light bulb. The only code stored is 41. I need to look that one up.
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Old 11-14-2018, 10:47 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

a replacement pigtail for the choke can be had at Rock Auto. check your other connectors while you're there. the one for the CTS is a common fail item too.

Code 41 is consistent with having run the motor with the ESC disconnected, which is done when setting the base timing. clear the code by unplugging the ECM (small lead with connector running from positive battery cable along right fender well into ECM harness). See if it recurs.
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Old 11-24-2018, 01:10 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

I made more progress today.

After being out of town with the family for a few days I finally got some time to install the new electric choke. Once I got it off I tested it again, and nada.

I tested the new one before installing and I could see it start to move after a minute or so. So I threw it on and it was a definite improvement. The choke opened up within a few minutes. But unfortunately the engine was missing badly.

So I ran out and grabbed a new set of plugs. Man replacing some of those plugs was a serious pain. But that did the trick. It started right up, idled high for a little while, then when I kicked it down it actually idled at a reasonable speed. It did die once, but it finally seemed to settle in to a reasonable idle speed. And I was able to back it out of the garage and drive around the block with no issues.

Now I can get a set of tires on it, get it align, get the wipers fixed and start driving it! Woot!

I also found a purge solenoid at the wrecking yard that I'd like to get installed at some point as well.

Thanks NAF and everybody for all the help so far.
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Old 11-24-2018, 10:29 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

good deal

for a new to me car, I'd replace all of the plug wires, cap and rotor. and fresh fluids everywhere.

post back with your progress
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Old 11-24-2018, 01:57 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Originally Posted by naf View Post
good deal

for a new to me car, I'd replace all of the plug wires, cap and rotor. and fresh fluids everywhere.

post back with your progress
Yup, a full fluid flush is on the radar. Wires were replaced by the PO and look good, I need to pop the cap and check it as well.

I need to figure out the evap issues, the tank is building pressure or vacuum and causing the car to stall. So that's moved up the priority list. This thing is heavy yo. No fun pushing it out of our intersection.
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Old 11-24-2018, 05:23 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

unlikely the tank has anything to do with stalling. the tank has an overpressure valve that will release when too much builds up. You can test it by putting an air hose on the tank return line (with the rubber hose off) and jucing it with some air. you should hear the pop and release of the pressure back there. anyways

when it next stalls and refuses to start, pour a small amount of gas into the carb (right in is fine) if it then fires and runs for a second you know it's a (lack of) fuel issue. if you haven't already though, replace the fuel filter. It's in the carb where it says fuel filter. the fuel goes through it inside out (you'll see) so it may look clean on the outside. be sure to use a 1" wrench with the 3/8th wrench on the fuel line and filter housing. it is easy for them both to turn when only using the 3/8" wrench which will F up your fuel line.
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Old 11-24-2018, 07:55 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

A buddy with more SBC experience came over and we got it started again. I think the new choke isn't adjusted properly.

But he figured out that the carb is leaking at the body gasket. So before I muck with it more I need to buy a rebuilt carn or rebuild it. I have always wanted to rebuild a carb so I might go that route.

Any thoughts on these rebuild kits?

https://cliffshighperformance.com/Quadrajet-rebuild-kits-and-quadrajet-parts/quadrajet-ccc-rebuild-kit

NAF I will also change the fuel filter. I think i might throw a new pump on too since I want to change the fuel lines too.
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Old 11-24-2018, 09:56 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Good choice with Cliff's kit. It has all the parts upgraded for use with today's gasoline. Buy his book also - invaluable info there.
For your fuel pump (assuming you have the block-mounted mechanical): https://www.rockauto.com/en/parts/ca...fuel+pump,6256
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Old 11-25-2018, 06:35 PM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

there's a thread here somewhere on rebuilding the carb....

https://www.thirdgen.org/forums/carb...-ccc-qjet.html

if the photos don't show, let me know. that was a long time ago.
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Old 12-04-2018, 01:53 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

THanks for the rebuild writeup, very useful!

I have the carb basically apart and need to clean it up. The main fuel bowl isn't that bad, but there are definitely some filthy spots and some nasty smelling old gas stuck in spots.

Two questions have come up.

First, - the throttle shafts seem pretty loose, and that sound common at this age. Is there a preferred vendor for a rebush kit? Cliff has them, as do other shops. Cliffs sounds pretty fool proof, but he's a bit more expensive. Anybody have any experience with any vendors?

Second - Cliff recommends adjusting the secondary linkages to get the throttle plates to open fully at WOT. Mine aren't quite vertical. Will I notice any difference on a basically stock LG4? It has a larger exhaust, but no headers. I'm going to go back and re-read his notes again when I log off.

Again thanks to NAF and all for all the guidance! I'm having fun and really hope to have it back on the road by THursday when my new tires arrive. But if I have to rebush it I don't think that's going to happen.
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Old 12-04-2018, 02:28 AM
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Fully open blades on a pretty much stock LG4? dunno about that one mate. Something bigger than a 305 might benefit from that.

When i did the shafts on mine, it took them apart (pain in the **** by the way) and wrapped some teflon tape over them and cleaned out the holes in the body, got them nice and smooth. That was several years ago now and theres not single difference between now and then.
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Old 12-04-2018, 07:31 AM
  #28  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

you should only need to install a bushing on the driver's side primary shaft. I've used a drill press to line it up straight.

I can send you a bushing or two if you have the means to drill it. I bought a pack of 20 or so several years ago, I've maybe used 10.
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Old 12-07-2018, 12:30 AM
  #29  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Thanks for the offer, I just bought a kit from Carb Junkies, it was about $30 and includes a reamer that goes through the entire carb body. I don't have a drill press (small garage, can't afford to lose the counter space) so this will work. After I'm done I might just pass it along to someone else, I'm tired of buying tools I only use once.

I also need to buy a gallon of carb cleaner and soak the bits while I wait for the reamer. Then it should go back together quickly. I hope.
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Old 12-07-2018, 08:18 AM
  #30  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

be sure to run some fine sandpaper around inside the bushings before installing the shaft, get rid of any burrs or irregularities that may cause a bind.

if you need any small pieces/parts let me know. I have a bin somewhere with some extras.
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Old 12-08-2018, 07:19 PM
  #31  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Originally Posted by Alfisti View Post

I also need to buy a gallon of carb cleaner and soak the bits while I wait for the reamer. Then it should go back together quickly. I hope.
do not clean non metal parts with carb cleaner ... just wash metal only parts .. plastic/wiring and rubber will get damaged with carb cleaner..

use MAF cleaner to clean non metal parts and electrical ..these electronic carbs are not like the old style non electronic .. carb cleaner on old carbs non electric will be OK but keep from the choke vac pull off's..

on the evap fuel tank canister I plugged up that 3/8 vac line going to the canister control valve.. reason is I had that fail 2 times and it sucked gas into the engine causing the converter to get damaged .. that multi evap valve is poor design .I saw your picture that 3/8 in port is plugged with a black cap.. good..

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Old 12-13-2018, 01:57 AM
  #32  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

I'm slowly getting it all back together after cleaning everything. I probably could have skipped the gallon of carb cleaner. I have only soaked a few small bits in it since the body pieces are too big.

Naf your rebuild guide is awesome. I have Cliffs book but it doesn't cover the computer controlled carbs very well, so I have just been following your thread. I forgot to take a photo of the choke linkage, but yours helped me get it back together correctly.

​​​​​​I wish Cliff had a better explanation for where all the small bits go, but I'm slowly figuring it out.

I also got the throttle shafts reamed out and new bushings installed. If anything the reamer was a touch too big, but I locked the bushings in with red loctite. Much less play now, and hopefully no vacuum leaks.

One question, what are these four brass tubes for? I had to find a really small pin to clean out the smaller ones.




​​​​​
​​​​
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Old 12-13-2018, 08:12 AM
  #33  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

two of the tubes are fuel pickup and should connect to the discharge tubes in the airhorn for the secondaries. the other two are emulsifiers if memory serves. they can be pulled out and reinstalled if needed. they are a press fit. sometimes when the carb is opened I'll find one or more laying down in the well and just tap it back in.

spray some carb cleaner through them and note where the passages connect.

I've poured the carb cleaner into a flat container similar the one you show in order to soak the bigger parts. course the 'green' carb cleaner they sell today is not the same foul stuff we used 20 years ago.
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Old 12-13-2018, 10:48 AM
  #34  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Originally Posted by naf View Post
two of the tubes are fuel pickup and should connect to the discharge tubes in the airhorn for the secondaries. the other two are emulsifiers if memory serves. they can be pulled out and reinstalled if needed. they are a press fit. sometimes when the carb is opened I'll find one or more laying down in the well and just tap it back in.

spray some carb cleaner through them and note where the passages connect.

I've poured the carb cleaner into a flat container similar the one you show in order to soak the bigger parts. course the 'green' carb cleaner they sell today is not the same foul stuff we used 20 years ago.
I thought about doing that, but I didn't want a big tub of that stuff open in the garage for a long time. Then again the spray stuff seems to be worse.

I was a bit surprised that the cleaner in the tub wasn't clear. Maybe it's eating away at the plastic basket? Oh well, doesn't matter.

I need to remove the top plate and look for the small o rings and replace those. Then hopefully I can button it up and reinstall it today!

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Old 12-14-2018, 01:07 AM
  #35  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

It's alive! (again)

I replaced the two small seals and the o rings on the lean idle stop, and reassembled the last of the parts.

First question any idea why there are two similar gaskets, one thicker than the other? I used the thick gasket under the carb.


Old gasket on left, new middle and right. I used the middle

I got the carb reinstalled, vacuum lines hooked up again, fuel line reconnected and throttle cable reconnected. After a little cranking it fired up and sounds smoother then before.

Once it warmed up the idle dropped a bit. But it was still too high. I was able to drop the idle down to about 900 RPM according to my dwell/tach. I think I'm reading it correctly, but I have lost the manual.

It's running well enough to drive around the block. But it surges while driving. I think the O2 sensor might be going bad, I will look at replacing it.

So what else should I look to adjust? I don't have any special tools. I plan to follow the label under the hood and check the timing first then adjust the idle with the ICS disconnected. What else should I check and adjust?

Thanks!



​​​

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Old 12-14-2018, 06:01 PM
  #36  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

OK

Make sure all of the ignition stuff is new: plugs, cap, rotor and wires. Check your base timing with the EST disconnected at the dist. It should be set to about 4 degrees advanced at idle. It may be difficult for the motor to idle with the EST disconnected, the idle bump solenoid should engage to help but warm it up some before doing this.

Reconnect the EST and observe that the timing should be around 20 degrees advanced at idle, there won't be any marks so you'll have to estimate. When rev'd the timing should advance. The exact amount is not important to measure but verify that it's operating properly.

Adjust the TPS so that it reads near 0.4 V at idle throttle setting and near 4.0V at WOT. The motor does not have to be running but the key must be on. Backprobe the top and middle connectors to read the voltage. Function test the TPS by observing a linear progression of voltage between curb idle and WOT. It should not jump around. TPS setting at idle can be adjusted with the little set screw behind the elbow piece that holds it down in the airhorn. It may be covered with a tamper proof screw. If you don't have the little tool to turn it, tap an appropriately sized roll pin over the head to turn it.

Connect your dwell meter to the green diagnostic lead near the blower motor. It comes out of the ECM harness that passes through the passenger fender. With the dwell meter on the six cylinder scale and the engine warmed up at idle you want to see a dwell that hovers near 50% or 30 degrees on your meter. When it wavers back and forth while idling, it's functioning correctly as the ECM adjusts the dwell in response to O2 readings.

Try it first with the idle mixture screws four turns out and the IAB four turns out. This is close to the factory setting. (You did pull the Idle Air Bleed out, clean it and check the o-rings on it? You also confirmed 1/8" of travel for the MCS and hear it click with the key on?).

If you get a steady dwell reading, the ECM is not in feedback mode, either because the motor is not warmed up (in warm-up mode) or the O2 readings are too far off for the ECM to see which way to adjust the dwell. In this case:

Start at 2 turns out on the idle mixture screws and 2 turns out on the IAB. Turn out the IAB about a half turn, waiting a few seconds to see if the dwell responds (by moving some). Continue until you're about 7 turns out on the IAB then go another half turn out on the idle mixture screws and 2 turns out on the IAB and repeat. Repeat this process until you get a responsive dwell then fine tune to where it's near 50% at idle. In the end you hope to be near 4 turns out on everything. Remember that out on the idle mixture screws richens the mixture while out on the IAB leans the mixture.

In the end you should see a dwell that wavers back and forth at idle maybe +/- 5 degrees or so. And the dwell should respond to a rag placed over the primary throat (richens mixture) by increasing dwell (leaning mixture). The idle quality may seem odd as it does so but this is normal. It may take some effort to get there so post back your findings. Recall that the dwell is the amount of time the rods are spent DOWN in the jets, restricting fuel (leaning mixture).

I hope I have not made any errors up there.

I like to cap off EVERY vacuum port while I adjust dwell. Then I reconnect them one at a time while observing the dwell (after its set) to verify that there are no vacuum leaks-a vacuum leak will lean the mixture and the dwell will respond by----

Fire away with any questions. It's been a while since I've done this so there's always the chance I'm leaving something out. If I were near I'd take a day with you. I used to get to do this stuff pretty regular. There are fewer around that know how these work. Once you get one dialed in it can be satisfying, which leads inevitably to cocktails.
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Old 12-14-2018, 06:06 PM
  #37  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

thick gasket is fine.
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Old 12-14-2018, 07:42 PM
  #38  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

I wish I had the info NAF just provided above back in the day. I might have more hair left now.
For me, getting the top of the carb back on without breaking the TPS stem was the hardest part.
Hopefully you were very careful and got that part right. Test it as NAF has explained.
The thicker base gasket helps combat heat-soaking the carb.
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Old 12-14-2018, 11:05 PM
  #39  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Originally Posted by naf View Post
OK

Make sure all of the ignition stuff is new: plugs, cap, rotor and wires. Check your base timing with the EST disconnected at the dist. It should be set to about 4 degrees advanced at idle. It may be difficult for the motor to idle with the EST disconnected, the idle bump solenoid should engage to help but warm it up some before doing this.

Reconnect the EST and observe that the timing should be around 20 degrees advanced at idle, there won't be any marks so you'll have to estimate. When rev'd the timing should advance. The exact amount is not important to measure but verify that it's operating properly.

Adjust the TPS so that it reads near 0.4 V at idle throttle setting and near 4.0V at WOT. The motor does not have to be running but the key must be on. Backprobe the top and middle connectors to read the voltage. Function test the TPS by observing a linear progression of voltage between curb idle and WOT. It should not jump around. TPS setting at idle can be adjusted with the little set screw behind the elbow piece that holds it down in the airhorn. It may be covered with a tamper proof screw. If you don't have the little tool to turn it, tap an appropriately sized roll pin over the head to turn it.

Connect your dwell meter to the green diagnostic lead near the blower motor. It comes out of the ECM harness that passes through the passenger fender. With the dwell meter on the six cylinder scale and the engine warmed up at idle you want to see a dwell that hovers near 50% or 30 degrees on your meter. When it wavers back and forth while idling, it's functioning correctly as the ECM adjusts the dwell in response to O2 readings.

Try it first with the idle mixture screws four turns out and the IAB four turns out. This is close to the factory setting. (You did pull the Idle Air Bleed out, clean it and check the o-rings on it? You also confirmed 1/8" of travel for the MCS and hear it click with the key on?).

If you get a steady dwell reading, the ECM is not in feedback mode, either because the motor is not warmed up (in warm-up mode) or the O2 readings are too far off for the ECM to see which way to adjust the dwell. In this case:

Start at 2 turns out on the idle mixture screws and 2 turns out on the IAB. Turn out the IAB about a half turn, waiting a few seconds to see if the dwell responds (by moving some). Continue until you're about 7 turns out on the IAB then go another half turn out on the idle mixture screws and 2 turns out on the IAB and repeat. Repeat this process until you get a responsive dwell then fine tune to where it's near 50% at idle. In the end you hope to be near 4 turns out on everything. Remember that out on the idle mixture screws richens the mixture while out on the IAB leans the mixture.

In the end you should see a dwell that wavers back and forth at idle maybe +/- 5 degrees or so. And the dwell should respond to a rag placed over the primary throat (richens mixture) by increasing dwell (leaning mixture). The idle quality may seem odd as it does so but this is normal. It may take some effort to get there so post back your findings. Recall that the dwell is the amount of time the rods are spent DOWN in the jets, restricting fuel (leaning mixture).

I hope I have not made any errors up there.

I like to cap off EVERY vacuum port while I adjust dwell. Then I reconnect them one at a time while observing the dwell (after its set) to verify that there are no vacuum leaks-a vacuum leak will lean the mixture and the dwell will respond by----

Fire away with any questions. It's been a while since I've done this so there's always the chance I'm leaving something out. If I were near I'd take a day with you. I used to get to do this stuff pretty regular. There are fewer around that know how these work. Once you get one dialed in it can be satisfying, which leads inevitably to cocktails.
I decided to skip straight to cocktails, or rather a good beer. It was a mixed kind of day.

I was trying to get it to run well enough to drive to the tires store today. Yesterday I had it idling around 600 RPM. This morning it would start then die relatively quickly. I pulled the choke and by manipulating the choke manually I got it to run long enough to warm up.

I undid the base idle screw adjustments I made yesterday which helped. But then I replaced the O2 sensor with a new one and that made a huge difference! I got it to run pretty well when warm and took it for a spin around the block. Man it's fun now, plenty of power at low RPM. Love the torque.

I threw the air dam on that I picked up at Pick n Pull and was able to drive it over to the tire shop about 6 miles away. The idle was about 1200 when warm, but it ran OK and never stalled. So I need to go back and double check the fast idle cam, choke and all that linkage.

But unfortunately I stopped for gas on the way home (and learned that the fuel gauge works, yay!) and with the stop and go traffic it overheated while idling waiting for me to open the garage door. Damn. Now the starter doesn't want to work, hopefully a whack with a hammer will get it going again.

So it seems to run pretty well at part throttle, but I definitely need to fine tune the idle settings. Unfortunately I didn't measure the MCS travel, I just set evereback to where it was before disassembly. But I read back through your rebuild instructions and now it makes more sense.

So I will pull the IAB and measure the MCS travel, then adjust to 1/8". I didn't pull the plug for the right stop screw so I will have to pull the air horn again, but I need to get that right.

I believe the IAB and both idle mixture screws are about 3.5 turns out from memory. Should I leave the MCS travel alone and just try to adjust the dwell?

Also how does the idle step up work? The car originally had AC but the compressor has been removed. The solenoid at the throttle linkage doesn't seem to do anything or have any resistance in the plunger. I will do some research on that.

Thanks again, I hope to sort the starter (and obviously the fan switch) then get back to tuning!

BTW, this is how bad the tires were. I wasn't sure they would make it 5 miles.



​​
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Old 12-15-2018, 01:43 AM
  #40  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Keep at it. It's a process. It can be very frustrating at times, but when you get it right, that will make it all worth it.
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Old 12-15-2018, 02:02 AM
  #41  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

OK after thinking about it for a bit, and the beer wearing off... I removed the lean idle plug (or rather it popped off) so I should be able to adjust the lean stop without removing the carb. And I didn't touch the rich stop. So if I use my digital caliper to measure the MCS movement through the air horn, I can adjust the lean stop to get the 1/8" of travel.

My carb rebuild kit didn't come with a small ruler but I have digital and analog calipers and a small machinist ruler.

I also finally figured out where the dwell connector should be, I'm pretty sure I saw it and assumed it was from the removed AC equipment. I will look for it again tomorrow

I will check the MCS travel tomorrow when I get time. Please let me know if my thinking is correct. I was in such a hurry to get the car running I glossed over a couple thing apparently. But at least I have good rubber now!
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Old 12-15-2018, 10:56 AM
  #42  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Originally Posted by NoEmissions84TA View Post
Keep at it. It's a process. It can be very frustrating at times, but when you get it right, that will make it all worth it.
I'm not frustrated yet, it's running pretty good and has made huge improvements already. The seller was talking about swapping the engine, I'm amazed nobody had just done basic maintenance like replacing the o2 sensor!

It's fun already, I can't wait to get it dialed in more. I love diagnosing and fixing issues instead of just throwing parts at a problem like most modern mechanics.
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Old 12-17-2018, 09:50 PM
  #43  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

I tried to post a more detailed update twice now and lost it when the photos wouldn't upload properly So just a quick question for now.

The lean idle stop screw plug came loose so I can adjust the lean idle screw to get the MCS travel to 1/8" or 0.125".

I measure about 0.130" at the moment, but adjusting the lean stop screw doesn't seem to be changing that measurement significantly. Its possible my measurement technique is off, I'm trying to use a set of digital calipers.

I should be turning it out right, to shorten the travel?

I set the lean idle stop screw back to where it was before the rebuild, about 4 turns out. So it was close initially.

Should I pull the air horn off and double check everything? Im going back to review the rebuild instructions and make sure I'm making sense of them.

Should I be able to get the 1/8" of travel by adjusting the lean stop screw alone?

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Old 12-18-2018, 01:33 AM
  #44  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

I definitely still learn better by doing. The official rebuild page was over my head earlier, now it’s starting to make more sense.

So I went back and reread this: https://www.thirdgen.org/forums/carb...e-rebuild.html

According to that the MCS travel spec is 4/32” +/- 2/32”. So I’m within spec and I will leave the lean idle stop screw alone and try to adjust it to set the dwell. Once I get home. It’s officially winter vacation so my girls are home and my mom is coming to visit tomorrow, but hopefully I will get a little time to play with it. I found the dwell connection the other night on the passenger side.

One more question. I still need to double check the fast idle cam and linkage as it doesn’t seem to want to drop down to the lowest setting without help. Maybe it’s just not warm enough yet. But is there any reason for the idle to just suddenly just when I’m not doing anything or touching anything? Is that the computer kicking in and trying to adjust the MCS suddenly? I didn’t think this carb had the Idle Control Solenoid system, just the AC solenoid and the AC is not only off, it’s not there.
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Old 12-18-2018, 11:58 AM
  #45  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

the 'AC solenoid' is also controlled by the ECM. It will engage under certain deceleration conditions to act as a 'dashpot' to reduce the emissions caused by a sudden throttle closing. a faulty TPS can confuse the ECM into engaging the solenoid at other times. best to unplug it for now.

if your idle is fairy high, in the 1000+ range, your motor could be on the edge of allowing the ECM to add timing, which also will increase the idle speed. the motor should idle fine at 700 or even lower, albeit with some apparent loss of idle quality as the ECM adjusts dwell. a good idle for an LG4 may be 700 +/- 'maybe' fifty rpm.

a thermal vacuum switch may also be opening as the motor warms up, exposing the motor to a vacuum leak past the switch. plugging every vacuum port while tuning will rule this out. leave the PCV connected though, as long as the ball bearing inside clicks when you shake it, the valve is likely alright.

the choke linkage-cam pieces were originally coated in Teflon (green) so that they would move freely. the Teflon can wear off and they can begin to stick. a shot of WD 40 now and then can help. verify that the choke is keeping the throttle off of the curb idle screw when you have a high idle. when the choke plate is straight up the little cam with the weight behind the choke cover should be able to fall down once the throttle is opened enough to take the spring pressure off of it. it may help to play with it some to help figure out how it's supposed to work.
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Old 12-19-2018, 02:10 AM
  #46  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

For now, disconnect the solenoid to take it out of the equation. Adjust the idle with the screw. Go from there as NAF said.
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Old 12-19-2018, 07:45 PM
  #47  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

I found one issue, I had the secondary lock out installed incorrectly.
​​​​​​

So I fixed that. The car started up pretty easily and settled into a reasonable if a little rough idle.

After a few minutes the dwell seemed to be hovering around 32, which looked pretty good to me. This was when the coolant temp was right around 150.
​​​​​​


I decided to let it run and keep watching the dwell, plus I wanted to see if the fan eventually kicked on. The good news is that now that I have corrected the temp switch wiring the fan comes on at 230 like it should and cools down the car.

The bad news is that the idle speed climbed a little and the dwell shifted closer to 5. I'm not sure why, I need to dig into that a little. Or do some adjustments once it's hot.


I didn't have time to maje any adjustments today, I only had a few minutes to play. But hopefully I can figure out why the idle is creeping up. I will start by looking for any vacuum leaks.
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Old 01-03-2019, 01:32 AM
  #48  
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Re: [email protected]#$ing an 86 LG4 Quadrajet

Yay, the kids are back in school and my mom has gone home so I can plug away at the Camaro again.

I tested the TPS last night and it's only reading 0.010V when warm and on the throttle stop. So I will need to pull the cap and adjust it. And I need to buy a new connector, this one just completely fell apart.

FWIW I believe you are supposed to measure from the bottom to middle, not top to middle. I measured about 5V from top to middle, but 0.010V from bottom to middle. When I open the throttle that value increased.




The Solstice Fairy also brought me a fancy new timing light so I can set the base timing. I will probably just start with stock and then bump it a few degrees once I have everything else dialed in. My old timing light didn't have the inductance clip, and wasn't a dial back. It worked, but it was a bit of a pain. I'm looking forward to the new one, plus it has a tach and dwell readings too.

I also swung by Pick and Pull today and grabbed a set of sun visors, a pair of speakers and a couple small pieces I needed. The car still had a set of 16x8 wheels on it I might try to grab, unfortunately they have junk tires on them and PNP usually charges for the tires, even if they're shot.
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