My first suggestions is to get Cliff Ruggles Q-Jet book and learn what everything in the carb actually does if you are not already familiar to the smallest detail with the carb. If you are sticking with a Q-Jet you need to know what the various passageways and restrictions are for. Any emissions Q-Jet will give better results with the fuel curve richened up and that requires a pin vise with sequential numbered precision drills, and some know how. Aside from the mixture control solenoid being used at idle/part throttle the E4ME Q-Jet functions much like any other Q-Jet.. If it were programming, unplugging the mixture control solenoid puts it into full rich mode. From memory the base timing on a CCC Q-Jet SBC is 6* BTDC, 10-12* would not be unreasonable with a cam change. The timing values programmed into the ECM are fairly low in both advance curve and amount. I made double the HP and had nearly 100 cubic inches more under the 307 CCC Carb and loved the way it drove. I eventually converted that car to GM TBI because it was far simpler.

I still think it is completely the cooling system. By self-admission you have stated that the fan is not pulling much air. You also have stated that it is wired to run 100% of the time. The fan could actually be blocking natural air flow going down the road. Also the most overlooked part is often the valance air scoop on the bottom of the radiator. If it is damaged or missing, overheating is almost a certainty on these cars. The stock size radiator core should not have an issue cooling a 350 much less a 305 if it is getting adequate airflow. My old G20 van used basically the same radiator core as these cars and towing a trailer uphill at or near sustained WOT it cooled just fine thanks to a massive mechanical clutch fan drawing in air at all times. It is completely possible that airflow is stagnant across the radiator even at 45-50 mph.

The weirdest overheat I even tracked down was actually a cooling fan that was blowing into the radiator rather than pulling through it. 5.0L Mustang would run cool at idle, cool at 75-80 mph, but overheat if driven 35-50 mph. If you are missing air dams, air guides, etc not amount of mechanical swapping the fuel/ignition system is going to keep it cool.

The best cooling system on these cars is one that is nearly impossible to duplicate now. The early cars had an actual fan shroud and a mechanical clutch fan that moved a lot more air than the electric fan setups that came after. The clutch fan setup I had always kept the temperature gauge under 1/2.

 

So Im on my dads account right now. (Im That86IROCZ btw). So I dragged him out to do some basic stuff today as its been 10 degrees out give or take.

I went out and checked #1 Spark Plug. It was decently ashy, so i cleaned it up a bit and stuck it back in.

Then we hooked up a test probe to the O2 Sensor. After being in closed loop, and warming up for 20 minutes or so, temps were 220, no boiling. at 800 rpm idle the sensor would bounce from .05V to .65V, and it would fluctuate about 3 times a second. Then at 2k rpm, It was holding .55V but fluctuating between .35V and .75V, didnt drop to 0v too often, much less than at idle but it still seemed a little jumpy. Brand new Bosch O2 Sensor btw. Didnt ground it out and goober it either.

Then we set Timing to 0 Deg BTDC at 700rpm factory spec. The cam is adv 4 degrees and the motor seemed happy. But it seems happy at pretty much any timing from 0-4 with the 4pin disconnected.

So now we decided to plug all vacuums except necessary stuff so no more carbon evap canistor, and we plugged some other bs. We found the Vacuum box above the brake filler to have a loose ish connection, we cut the line back a bit and put on the 4th gen vacuum box from a 95 Formula. Same dimensions and all, but it fit snugger on the nipple. Car idled muchhhh smoother and seemed decent. We took it for a quick drive, and it seemed solid. Still overheated after 15 minutes or so, but it seemed happy. We have to reset the curb idle as it wouldnt kick down from mid idle, so it was 1800 for that drive. but we barely idled. It didnt boil over after the run. and it fired right up when we adjusted the idle again. This was about 10 minutes ago, just waiting for the car to cool again to see what idle will be like.

The only weird part on the drive was this. So we have a big half mile hill like 35 deg incline. So we climbed it starting at like 220 on the dial. At the top it got up to around 240, then it took off once we climbed it, went all the way up to red. We pulled a u turn and started heading down the hill. We basically engine braked down the hill and the car cooled all the way down to 220. It went from red 260ish to 220 just by keeping it in 3rd and not touching the gas. It just plummeted while engine braking, like ive never seen. Then pulling in the house it slowly crept up, but shut it off in the driveway. A little bit of gurgling in the upper hose, and the overflow coolant was a little bit higher than full hot.

Im gonna go pull the plug after the run, and hopefully it isnt ashy, before the run it was shiny new with scotch brite, and drop a pic in the chat.

Thanks for all the support and hope we start getting some better results.

 

#1 Plug looks a hell of a lot better than before
I have some more pics too
#1 Still

Still #1

 

I’ve installed and tuned bigger cams than that one in the L69s and LG4s with the computer quad. However your cam is starting to get on the borderline of needing more than just idle mixture screws and air bleed valve adjustments. Below are the adjustment points in relative order of “need”. Even the smallest of performance cams will typically need idle mixture and air bleed valve adjustments. Bigger cams, maybe even yours, could require a throttle position sensor adjustment (because you may have moved it out of range when raising the idle speed with the adjustment screw). The bigger cams (bigger than yours) will almost always require adjustments to the lean and rich stops to run right. NAPA used to carry the idle mixture adjustment tool and the air bleed valve adjusts with a flat screwdriver.


I’ve installed over 14 different cams in L69s and LG4s back in the day and tuned a lot more computer carbs than that. That’s probably a decade before the guy you talked to at Comp was born. So, don't let that guy discourage you - your cam will most definitely work with the computer carb, assuming you “tune” for it (at least the idle mixture screws and idle air bleed valve).

I haven't seen the book Fast recommended, but this is the same book I bought back then and recommend it to those starting out. The secondaries of the computer quad works just like the non-computer version, so all the information about secondary tuning applies to the computer carb. eBay has one that looks to be in decent shape for a decent price.

Rochester Carburetors HP Book By Doug Roe - eBay

Hope that helps.

 

I will add some more info reading back through.

ALL the smog era Q-Jets will be calibrated lean from GM and all of them will need adjustments.

Idle Mixture screws. Stock setting is 3-3/4 out and I generally go 5 after resizing the idle down tubes, idle channel restrictions and idle mixture screw openings. Some setups need as much as 6-7 turns out on the idle screws. With those metric idle screws, factory ICR and idle down tube sizing, I have seen some non computer engines like the L82 factory set as much as 7.5 turns out to get enough fuel to idle. I would open up the idle and off idle transition slot fueling a bit because you can always lean it back out as needed with the idle air bleed screw on top. You can take away fuel by adding bleed air, but its really tough to add it the same way.

Bypass air. Once you start having to really open the throttle plates with the idle speed screw, the carb needs more bypass air. You are going to have the same issue with a mechanical version as well. Bypass air allows the carb to properly meter fuel off-idle without having to crank up the idle speed screw. You can actually get so much velocity on the venturis that fuel starts to pull through the main metering circuit at idle aka nozzle drip. Bypass air is air drawn through voids in the casting and metered by orfices drilled into the base plate. It allows air to bypass the primaries without being drawn through the venturies and boosters. Typically need to go from 0.060-0.080 up to 0.95-.110 on the bypass air for a cam that size.

Accelerator pump, get performance one with a longer stem and stiffer spring. Then drill the discharge holes 0.030-0.032" makes sure you use a new check ball after using the old one to burnish the seat. Fuel needs to discharge from the accelerator pump instantly when the throttle is moved.

Timing...The 85 TPI 305 I converted to carb which for all practical purposes makes it a L69 liked 35* total advance at WOT. The LG4 computer I located the spark tables in only commands about 26-28* of timing at WOT and only in the mid 30s at cruising speeds with the initial set at 6*. With a modest cam I think it will be happiest in the 10-14* initial range. Set it at 12*, shut it off, reconnect the EST, remove the negative cable to clear out the codes, then refire it. Bring it up to ~3500 rpm no load and check total advance. My guess is it will be in the low to mid 40s which is where it needs to be.

Also something that gets messed up often, when adjusting the mixture feedback, make certain you use the 6 cylinder dwell meter. 30* is in the middle, but I tend to error on slightly higher. Higher value means the base calibration is richer overall and there will be more fuel available when the carb enters open loop for acceleration enrichment.

If you think it is lean fueling causing the overheat, unplug the mixture control solenoid and drive it around a bit. The carb will default to full rich when the solenoid is unplugged.

 

Fast 355,

Thank you for this post. I was looking for this kind of input. I am an engineer and my feeling about this car is that we have made enough changes, or have missed something in the set up (or a combination) that we have moved the carb/distributor/ECM and EST to a place where they are causing the overheat.

I have had many CCC Qjet cars (81 Grand Lemans, 83 Cutlass Brougham) but this was back in the day, 30 years ago when wife and I were scrapping by and I kept them running on a shoe string. Never worried how they ran, as long as they ran. Over the last ten years, I started in earnest on my car hobby. And I try to be a purist. There is a certain pride to make it work as designed (that's the engineer talking...my evil twin, the finance guy tries to control the budget).

I restored a 1990 L98 C4 Vette and my son and I restored a 1996 Z28 LT1. The L98 was a great car but it seemed every time I turned around, another switch or sensor would crap out and I spent as much time wrenching as driving. GM had many firsts on those C4 and sometimes, the control systems were overly complicated to do otherwise simple things. I sold that two years ago, but it was running like a top when I sold it and it was really for space, and there was nothing left to do but polish and drive it. Polo Green 6 Speed (Gretrag) with Saddle Interior.

The 1996 Z28 convertible was a 6 speed B/W T56 and was my son's. And he decided one day he wanted a hardtop third gen and the 1996 was sold last year while we started the restoration of this IROC. This Iroc is LG4/T5 Open Diff 3:23. We swapped in a Fourth Gen Auburn Posi with Disc Brakes and we re geared it to 3.77 because the Formula Bird we pulled it from came with 2:73 gears. Full rebuild on rear by me and full rebuild of motor by me.

I had bought an 86 El Camino a few years back (this was a bucket list car) and it was basically the same motor/carb as this 86 IROC except it was automatic. I had carb problems with that (bad choke setup) and I got that all settled out. However, due to space constraints, I flipped the El Co because I was starting a 79 C10 Step Side street rod project which is frame off, nut and bolt build. Chassis and drive train is assembled and I am starting rust work. When weather warms up, I will rig up a radiator and ignition and brake in the GM Performance SBC and break in that cam.

I have an affinity for tools and I have the Ruggles Book and the Haynes Book and I believe I understand the multiple circuits these carbs have. When I started reading the factory service manual for this IROC, I saw all the tech tools that I did not own so I started shopping on ebay. Below is the collection I have amassed over last year. Including the tools, the rebuild kit, float and new TPS for this carb, I spent less than half of what I would have spent on a rebuild carb from Rockauto. I bought a third DVM (already had two) which had the dwell scale and I am aware that it has to be on 6 cylinder scale.



When I rebuilt the carb, MCR lean idle was set with the brass gauge and the rich idle was set for 4/32" travel per the FSM using the black plastic gauge that measure float. The IAB was set using the umbrella gauge that set the IAB relative to the MCS plunger on full lean and the Idle screws were set 3 turns out.

Choke was with the angle gauge. The lead plugs were JB welded (in case they were leaking).

Yesterday, on a 10 degree day in NJ, after sitting for 24 hours, the car started after one stomp of the pedal to set the choke and only 3 to 5 seconds of cranking. Went right to the high set idle and warmed up.

The TPS was replaced in March because the prior had failed. FSM states to set it at 0.,54 on the DVM and it should sweep smooth to FOT. At FOT, we get over 4.2 V. Not getting 5, but we are starting at 0.54 per the FSM and there is no more travel in the throttle.

Yesterday after many suggests, we took the idle back to 0 deg BTC as per the Hood Sticker with the 4 pin disconnected. We set curb idle at 700 to 750 RPM and recallibrated the TPS. We chased all vacuum connections as naf thought we could have one and capped off everything on the carb except:

1. Secondory choke pull off (this is on front passenger side of carb. It pulls the choke off high idle when there is enough vacuum and prevents the secondary blades from tipping unless you stomp it and drop vacuum. The pull off is new and holds vacuum
2. The PCV Valve connection
3. The Power Brake Booster
4. The manfold connection to the HVAC reservoir. The dash works properly and I have traced the full vacuum harness. We had the entire dash out of the car to do rust repair and clean out mice nests.
5. The Vacuum Senser on the back of the carb which goes to the sensor on the firewall by the wiper motor. This was tested and hold vacuum.

We do not believe there are any leaks. All hoses are new and all connections are tight. All other ports on the carb are capped.

The car idled ok (little choppy)

While idling, I have the little black BT Tools float scale and through the top vent, we have the 11/32" float level. Which I .set with the BT Tools Contraption in the Blue Box in the Picture when I rebuilt the carb.

That same scale confirmed the 4/32" TPS travel.

We ran the dwell checks per the FSM.

The car dropped over 300 RPM (almost 1000 RPM) when we reconnected the MCS with the Dwell connector grounded. We then ran the dwell check and it was bouncing between 29 and 31 degrees (6C scale) with the IAB turned out from the base position with the left and right idle screws turned out 3 turns.

Recognize the above is already a long reply but I want to share the data.

Today, we went back to the car and started over again. I thought my timing light was suspect so my buddy brought over his which is the same.

We took the timing up to 6 degrees BTC and set the idle to 750. When doing this, we got error 23 and 41. 23 was the TPS so we recallibrated that again. Code 41 was for the 4 pin disconnected I think. We reset the ECM and started up. Drove the car and it ran good but it still ran hot to an overheat condition.

One thing we have established is that the electric fan will never come on when connected to the temp switch on the pasenger side head. This concerns me. It could be a bad switch (likely) or poor flow through that head. I may pull the thermostat and use my boroscope, tracer to confirm the head to manifold port is not blocked.

I am confident the driver side head is good because we watch the gauge sensor drop quickly when the Tstat opens.

After resetting the timing per above, we cleared the ECM and reconnected. With the 6 degrees advance with the 4 pin disconnected, we got around 32 degrees of advance at curb on my gun to hold zero mark (so 26 degrees net) idle with the 4 pin connected and 44 degrees of advance (net 38) at 3000 RPM.

Still no solution here.

Regards,

pcopp

 

OK,

I had just finished the above reply when my son asked me take a test drive. The only thing we did was disconnect the MCS solenoid. The curb idle went to 1100 rpm.
Electric fan was jumpered to 100% on. and the SES light came on.

So, son idled the car for about ten minutes and gauge did not go above 220. We took the car for test drive and drove car up a 40 degree hill twice and drove out of town about two or three miles. Son took the car to WOT through the gears and the temps stayed between 220 and 240. After the second hill climb, the temp went above 240 but on the downhill return, the temp recovered to 220. We took it for another hard WOT pull and the temp went up. We pulled in the driveway and idled the car. It stayed just above 240, but it did not take off. We shut it down and it did not diesel.

No coolant leak from the radiator cap and the overflow bottle was just above "full hot". I felt the upper hose and it was very hot and there was some bubbling/boiling in the hose.

We pulled the Codes from the ECM and we had code 23 MCS circuit grounded or open whivh was due to the MCS disconnect.

Any thoughts now that we have brought the temps to a manageable condition?

pcopp

 

Hello, just adding another question to my dad's reply.

So we know that the car didn't overheat with mcs disconnected. so it's a lean engine condition causing overheaoverheating.
Now with that said, we have a e4me ccc quadrajet. would changing the lean stop and rich stop out until the engine runs good be a way to get around needing to jet the carb.
the O2 sensor is just a run of the mill one, and dwell didn't seem to fluctuate too much. outside of adding a diode or resistor to flub it's value so dwell stays the same, is there actually that much variance that the computer can control if we do back it out some.

It ran decent with mcs fully out so I'm wondering if just setting the top and bottoms higher would fix that issue. we set the carb up to factory specs. so if we just add some leeway on it I'm betting that it would run good.

I checked the guide for tuning for performance on the ccc quadrajet and it seems like I should have no problem fuel wise with this carb. does it sound like I'm looking in the right direction to fix this lean issue. I could even install a afr gauge with a wideband to really dial in the engine.

 

I bought an 88 C1500 many years ago from a guy and he could not get it to run unless the thermostat was removed.With the thermostat out it ran cool but with one installed it would run hot going down the road .Turns out it had these intake gaskets on it and they were installed with the flow restrictors at the front of the engine instead of the rear of the engine. I am not saying this is the case for you,just something I ran into.

 

That's why I asked in a previous post what intake gaskets were installed...

 

Yep Intake manifold gaskets installed proper way. at least verified on driver side of block. we are pulling the temp switch on passenger side as the fan doesn't always get ground from it, so either the switch is bad or flow is bad on passenger side. when we pull it we'll boroscope it to ensure it doesn't have rtv limiting the flow.

I doubt that it is getting bad flow as with mcs disconnected we now don't have the overheating issue.

Our plan as of right now is the following.

We have the 305 E4ME CCC Carb and computer controlled distributor too, but we have a 79 Rochester 350 quadrajet as well, non ccc. we have a vacuum advance distributor for the 79 carb as well.

We will
Turn out idle mix screws on E4ME I'm thinking 5 turns on bothAdjust IAB, TPS, and right now the lean and rich stop screws are nuts on factory settings. *Should we adjust these as well?*
See how the carb runs with idle mix screws out more.
We are planning to swap in the dual lt1 fans on the radiator regardless of carb.

If the car overheats with E4ME after adjustment it's time to switch to old-school vacuum advance stuff.
I doubt we will have any issue with that stuff, but we will run into other setup issues, so if we just have to open up the E4 more that would be ideal.

Has anyone had experience fattening up a CCC quadrajet?

Will adjusting the two screws on the front of the carb help with part throttle lean too?

At this point in time we are really looking for enriching the carb in general, any tips on getting there would be awesome.

 

I had to knock off a few cobwebs since most of the work I did on these computer quads was 37 or so years ago.

After thinking about it, I only did one cam change on a LG4 and went with a cam I didn’t normally have to mess with the lean and rich stops. However, I did have to crack open the carb and found the float was set fractionally lower than the L69 carbs and it had 74 primary jets as opposed to the 76s in the L69s. Up until that time I though the carbs were the same in the primary fueling. So it makes sense to me now why you would need to adjust the lean and rich stops.

So, yes, I do think you’re going to have to raise the lean stop and rich stop. I’d go a 1/4 turn up on the lean stop and 1/2 turn up on the rich stop and see where that puts you. If you see you need more adjust both in 1/4 turn increments. Worse comes to worst, I’d get some 76 jets. I know you SHOULD be able to get things right with those.

Also, the front mixture screws affect both curb idle and off idle mixtures (not really part throttle) while the air bleed valve affects only the curb idle. I used to hook up a vacuum gauge and go in and out on the front mixture screws to get the highest vacuum reading. Adjust these after each lean and rich stop adjustment

See if you can find some DR secondary rods (that came with the L69) or a set of CP rods, which is fractionally richer. The DRs and CPs are hard to come by so a set of BA, DH, or ED rods would work a lot better than the CH secondary rods from the LG4. Also, loosen up on the spring for the secondary flap so they’ll come in earlier (which will help a little with part throttle). Filing down the secondary air flap tang to get them to fully open will help WOT with the richer rods. See if you can find an H or G hanger also

While I’m at it, check the opening of the throttle bore plates to make sure they’re fully opening. Most I worked on were not. Won’t help with your lean issue but it will help the performance if they’re not already opening all the way once you get the carb dialed in.

The lean mixture might be contributing to it running hot, but I can’t help but think there are other issues. It really does sound like a restriction somewhere or a very persistent air pocket.

 

if the dwell is varying and responding to O2 sensor input then the ECM thinks the mixture is right. if you go dinking with other things to richen it you'll just have to lean it back out with the IAB to get proper dwell. All of those settings just get it in a happy place so that it can adjust the mixture with it's only tool...the MCS dwell.

that said, what's the dwell doing at cruise? and part throttle? It's possible that it's going too lean for the MCS to compensate during other driving conditions. You want to get the carb set up so that the mixture is near its happy place during most driving conditions.

run it with the dwell meter connected, see what's what.

the lean condition that I recalled came from No Transistors (I think-a search here only went back a few years).

That LG4 ran lean even though the dwell would respond properly at idle turned out to be leak in the accessory vacuum system, the connection to the intake manifold port between carb and dist, easy enough to plug that one temporarily. never figured out how that would affect it, but he said fixing the leak solved his issue.

 

[QUOTE=naf;6492488]if the dwell is varying and responding to O2 sensor input then the ECM thinks the mixture is right. if you go dinking with other things to richen it you'll just have to lean it back out with the IAB to get proper dwell. All of those settings just get it in a happy place so that it can adjust the mixture with it's only tool...the MCS dwell.

that said, what's the dwell doing at cruise? and part throttle? It's possible that it's going too lean for the MCS to compensate during other driving conditions. You want to get the carb set up so that the mixture is near its happy place during most driving conditions.

run it with the dwell meter connected, see what's what.

the lean condition that I recalled came from No Transistors (I think-a search here only went back a few years).

That LG4 ran lean even though the dwell would respond properly at idle turned out to be leak in the accessory vacuum system, the connection to the intake manifold port between carb and dist, easy enough to plug that one temporarily. never figured out how that would affect it, but he said fixing the leak solved his issue.[/QUOTE

You want it to have a good air/fuel ratio with the mixture control solenoid disconnected. I typically shoot for 13:1 on acceleration on the primaries. As I mentioned before you cannot add fuel with the mixture control solenoid, it has to be there to start with mechanically. Then you adjust the air bleed to get it back to where the ECM can control it at part throttle. I forget the exact TPS that the mixture control solenoid is disabled but it is well before the secondaries open.

 

It sounds like you did exactly as I did. I made this diagram. It might help you.

 

If you still have the CCC carb on the car, get the idle mixture screws to 5-7 turns out.
You shouldn't still be at 3 turns.

 

OK, will do.

 

Ding Ding Ding.......

Been meaning to write you a reply but moved on to other stuff......

That was our problem. I screwed up the install of these gaskets. I boroscoped the intake through the tstat port and sure enough, install gasket backwards.

Put new Fel Pro gaskets which are open on both ends (of course distributor end does not matter) but that makes them idiot proof, and problem gone.

I must have been in a rush and made the critical error when assembling.

PCOPP

 

And there you have it!
'Glad you got it fixed...