We just got an 1984 z28 with the stock 4brl carb on it. It has the LG4 V8 in it. The guy we got it from looks like he pulled off the air pump and left a lot of vacuum hoses going nowhere. As a result the car is having trouble idling. I was hoping someone would have a picture or could explain exactly where all of the inputs and outputs on the carb go. There seems to be a lot focus around the EGR valve (which at this point im pretty sure is not connected properly) and the PCV valve which we think we may have hooked up right (?). Any help would be appreciated.

 

Welcome aboard thirdgen.org.

On the "FAQ" forum, there is a thread about vacuum diagrams. If the sticker from the factory is no longer under your hood, you can look there for the information.

The EGR is activated by a solenoid that is controlled by the ECM. That may be why it doesn't look right to you.

 

Thank you so much. I hadn't looked there yet. I don't mean to be redundant but right now I still think my EGR diaphragm is hooked up in the wrong place. Correct me if Im wrong but...

1 is my EGR diaphragm (or what i think to be) and two is where its currently hooked up. The arrow is to the front of the vehicle.

EDIT: I think that he may have removed the solenoid from the EGR valve. Is that possible? The car runs without it but not well :/ And the ECM may also be unwired, there is a four conductor connector hanging in the left rear side of the engine, by the power brake master cylinder. Is this important?

 

Yes it is possible to remove the EGR switch, just remove it. Just a short answer to that one. I have never seen a hack job like that on the EGR hose. If your car is like the 85 I had or my 86, then yes it should have a EGR switch mounted on the R/S firewall. Pull and cap the vac line hooked to the EGR valve just to see if this helps the idle condition. Looks like the EGR has constant vac applied with this configuration. EGR valve,when properly connected, does not even funtion at idle. Try this first.

Joel

 

Thanks, we pulled the vacuum hose and plugged it with a golf tee and that seemed to help the idle quite a bit. Now tho, my idle is very erratic and not consistent at all. I was reading through these threads a bit and am hearing a lot about fast idle and slow idle. Not sure what all that is. Some times when I start my idle will be around 750 (still erratic and spikes a lot) and other times around 1200.

 

OK. For now don't worry about the EGR untill you get further along. Spend a little time looking at the carb for any more loose vac lines and correct/plug as needed.
And as five7kid suggested read the material on these carbs. The fast idle linkage is on the R/S by the choke pull off. This might be hanging, but there many things you need to check. What was that plug/harness you asked about? Possibly the EST? Need to button up some of these loose ends.

good luck
Joel

 

Four wire connector by the brake booster could be the four wire connector to the dist. There should be a short cable coming from the rear of the distributor that is connected with a four-wire inline plug. An '84 LG4 shouldn't have an EST (no knock sensor) nor an electric fan which would be other four-wire connectors near that location on later models. If this connector is disconnected your dist is running on only the most basic timing curve (step really).

If this car is new to you it's a good idea to replace all your plugs, wires, cap and rotor prior to attempting any other diagnosis. Next on the agenda would be to properly set ignition timing (the above four-wire connector to dist is disconnected to set base timing). After all those check out you may consider plugging each vacuum port on the carb and manifold then re-connecting them one at a time. The leak will usually reveal itself with a noticeable change in idle.

A dwell meter or scan tool is a good investment when your car is running poorly. If the carb has not been tampered with (plugs are all still there), appears to be in relatively good shape (clean and shiny), driveability is good and your mileage is in the low 20's you can probably skip the investment. Otherwise the meter will help diagnose sensor problems and get your carb in proper adjustment, especially if a rebuild is needed.

 

The power to your electric choke isn't hooked up. You can't expect the choke to operate properly until it is.
It's very likely, since it looks like the EGR is hooked directly to vacuum. If that is manifold vacuum (always has vacuum), idle will never be correct.

What does the distributor look like? Does it have a vacuum canister on the base?

Some more photos of the carburetor, distributor, and each side of the engine may help to figure out just how badly this poor car has been abused.

 

Did we miss the rear vacuum break that tells us this is not a ccc-qjet and probably not the original carb? I know I did when I first looked at it. Export model?

Export models used a different type EGR valve that, I've read, relied on a back pressure signal as well as vacuum. I can't say with certainty that the plumbing there is not 'partially' correct.

Abused? I've seen abused and it was never THAT tidy. Let's not bash. I've recently expended great effort avoiding the bash. Not here in this thread, Ryan but nearby.

 

It appears the choke has been turned an extra 90 degrees so that it's always open.

This car should not have a rear vacuum break if it's a US model.

 

My use of the term "hack" in post #4 was inappropriate, not my usual language when trying to help with a problem. I did notice the choke pull off looking different, but the bell did not ring! Had too many "irons in the fire" today.

Joel

 

Who else wants a photo of the entire setup?

Another blast from the past, been missing some of the old, to me, posters.

 

I think hack is appropriate in this instance.

 

Haha wow guys, thanks for all your input. As far as the distributer goes, we just put in a new MSD distributer and redid all the spark plug wiring with looms. When we got it, it was less than organized. Anyways, on to pics. Ive labeled all the ports I could find. It would be nice to know where they go...
Thanks again guys.


----------
And...




BTW, Ive been thinking of rebuilding the carb, think it would do much good?

 

Mechanical q-jet, not the original carb if that is a US model. I suspect it's been converted because the water neck has the Coolant Temp Sensor. You've got a vacuum advance dist though so your ecm isn't doing anything anymore. If you've got an automatic transmission you may want to look into controlling the lockup with a vacuum switch set up as the ecm will no longer lock it.

The four wire connector near the brake booster you mentioned earlier is likely the four wire connector to the computer controlled distributor that was once installed there. It's no longer needed.

#6 is the thermal vacuum switch for the evap canister that should be front driver's side. It should be run thru a purge valve set up that I don't see.
#3 is a vacuum port that is normally connected to the hot air stove pipe flapper in the air cleaner horn.
#4 is the bowl vent for the carb, normally connected to the evap canister.
#5 is normally connected to the EGR valve, through an electric switch controlled by the ecm on ccc models.
#7 is your brake booster vacuum source
#8 is a manifold vacuum source, connection would depend on application. Can be used for the vac can on the dist.
#9/10 is a rear mounted vacuum break. I can't remember how that should be connected. The break when installed in front is normally connected to number 3, with a tee on ccc models.

 

I love you.

 

Watch it - this is a family- & workplace friendly Board. . .

 

Im having a hard time believing that the guy we bought this from took the effort to put in a separate carb, that is non stock. I'm almost positive it's not an import model. I noticed you mentioned one of the reasons you suspected it being a non-stock carb was the collant temp on the water neck. Well, the sender unit wasn't working properly so we had to replace it, so ya, that was us. But you would probably know better than I, is there any way of veryfing the origins of this carb? Also, Five7kid mentioned the electronic choke was not hooked up properly, would that mean that it is not in fact a mechanical carb as mentioned earlier? And how would that not being hooked up affect the proformance, and how can it be remidied? As always thanks so much for your help.

PS: I just looked up the VIN (1G1AP87H0EL******) and apparently it was made in the US...

 

It is not a computer controlled carburetor. Mechanical q-jets also came with electric chokes. The water neck CTS is only used by the ecm and wouldn't be in place in a factory mechanical carb setup (unless it was used in some way, on some models, for the carb enrichment solenoid??? but your carb doesn't have that anyway). Looks like you've also got the connector running across to the O2 sensor, which, if present, would definitively tell you that this carb has been changed.

You say the CTS sender wasn't working properly, in what way? Your ecm, if still there and getting power, should be throwing all sorts of codes-'course the check engine light could be out or removed.

Canadian and other export models were sometimes shipped with a mechanical system. I'm 99% certain your original carb and distributor have been replaced with non-computer controlled versions.

 

Hi,
The CTS wasn't giving me a temp reading, however when i grounded the wire the temp shot up, so i figured the wiring was good, sender bad. I replaced it and now i have a working gage . I think it may be time for a couple more pictures, namely of the four wire connector. Also, what do you suggest I do about the electronic choke not being hooked up? Can the wiring be easily obtained? Where does it plug into? One last thing: As I said I checked the VIN number and it said that it was made in the US, namely Califonia. So that would mean that the original owner would have had to have swapped the carp and just pulled out a lot of the ECM stuff?
EDIT: Also, is there any way of (namely by serial or other ID number) that we can see what kind of carb is on there?

 

Ok, here are the pictures



This is the right rear side of the engine compartment. Is that the ECM?



Here is our magical four wire connector.


This is just coming out of the firewall... any advice?


And last and least, what goes in this hole next to the PCV breather?

Thanks so much

 

The photo I quoted above, just above the end of your arrow is the connection to the electric choke.

The CTS does not go to the temperature gage. The temperature gage sender is in the driver's side head. The "Coolant Temperature Sensor" is in the thermostat housing as stated above.

That's the manifold vacuum sensor. The ECM is behind the dash above the passenger's legs.

Correct. It won't be connected to anything anymore.

Looks like the windshield washer hose.

There is supposed to be a temperature vacuum switch there to operate the flap inside the snorkel.

 

You can pull numbers off the driver's side rear of the carb that might be able to identify where it came from. At this point, though, it's unlikely to provide you with useful information. Q-jets are essentially all the same except for different size jets and rods inside. Knowing what jets/rods came with that particular carb DOES NOT get you any closer to knowing what jets/rods are in it now-looking it up would actually only tell us, maybe, what motor it was attached to.

What has been removed is a carburetor that adjusted the primary mixture based on throttle position and vacuum readings. The O2 sensor was used to trim these settings. The ECM also controlled timing advance with the computer controlled distributor and torque converter lockup based on engine speed, throttle position and load. At this point it's probably best to work with what you've got, especially since you have a new mech dist.

You may want to check whether the po installed an alternate means to lock the converter. Proper operation of the lockup will significantly improve the service life of the tranny.

It is possible that the dash guage was wired into the CTS on the water neck, although the factory location for the sensor to the guage is in the driver's side head.

The electric choke heater wire should be a single wire coming from the wire loom that crosses (or used to) the pass side valve cover. Once you identify a candidate it can be verified by ensuring that it ONLY provides 12 volts when the engine is RUNNING. The choke heater circuit pulls power from the alternator only when it is spinning, to keep from inadvertently opening the choke while the ignition is in 'run' but not started.

 

Hey guys sorry I havent replied in a while, Ive been very busy with work.
Anyways, after doing a leak down test and coming back alright, we decided to just pull the carb off until we could rebuild it and put an edelbrock one on. Car runs great now, except the transmission is completely lost on it's shift points. I imagine cause a couple of the vaccume lines didn't have ports on this temparary carb. Anyways so basically all my problems were solved with a different carb, so im going to rebuild the old one and stick it back on. Thanks so much for your guy's help.

 

The transmission relies on a TV cable attached to the carb for throttle position. Proper alignment and range of travel for this cable is required to maintain correct shift points. An aftermarket carb may not have the proper connection to establish the RANGE of travel for this cable. An aftermarket piece is sometimes required with edelbrock carbs.

The TV cable should be the inner cable with the plastic clip which is a different connection from the throttle and cruise connections.

Maintaining proper geometry is extremely important for the tranny and its life.

IMO the mech q-jet is the next best option for you.

 

Ya I was just about to post about that. We are going to rebuild that mech q-jet and set that up right whether it be with a new plate or not...

As far as the q-jet that is on it (the one in the pictures) it's not the stock one *just like you guys said*. Model number 17081226. Apparently off a 1981 chevy truck. seems to be compatible enough tho... any ideas on how to get the torque converter lock up or electric choke to work?

 

Electric choke: Find and hook up the wire to the choke thermostat terminal. If memory serves, it's a greenish-blue wire. Then rotate the thermostat (loosen the three screws) so the mark lines up with the center mark on the housing, or the choke butterfly goes all the way closed (you'll need to hold the throttle open slightly if you try to close the butterfly while rotating the choke thermostat).

TCC lock-up: It's discussed often on the Transmission and Drivetrain forum. Basically, you can hook up a manual switch, use a 4th gear pressure switch, or get a kit from Summit/Jegs/TCI/etc.

FWIW, I'd personally never remove a q-jet to install an Edelbrock Performer. Major downgrade IMHO.

 

Choke may be in working position now. Appears to be closed and choke cover has been riveted back on, or factory rivets never removed.

Do a search for lock up switch. A vacuum switch and some wiring is all that is needed. Make sure you continue to wire it through the brake pedal switch.