Hi everybody !
I would like to ask for your help to debug my CCC quadrajet from 84 Firebird

Advance set to 8 degree with four wire connector disconnected (on the hood sticker, it's only 6 degree)
New TPS set to 0,5 V
The carburetor has been rebuilt (gasket, ultrasonic cleaning, throttle shaft ring). The factory settings are still sealed. (IAB and mixture screw)
New catalytic converter
New oxygen sensor, (AC Delco)
New coolant temp sensor
New TVS for EFE (EFE close when the engine is cold and open when the engine is hot)
Choke work (Close when the engine is cold, and full open when the engine is hot)
All vacuum lines are news
Smog pump blows into the exhaust manifold when the engine is cold and in the catalytic converter when the engine is hot

Cold start OK; choke and high idle OK at 1100 rpm, pressing the accelerator reduces the speed to 800 rpm in neutral
After 5 minutes at idle, the choke is wide open and the idle speed remains at 800 rpm. When accelerating, the speed always drops back down correctly to 800 rpm

During the first kilometer (miles) of driving, everything is OK. Problems arise when the car is warm (after driving 20 km).

When I maintain a steady speed of 50 km/h (31 mph), in 4th overdrive the car hesitates and shakes a little. When I accelerate fully, there is no dip or acceleration gap. When I shift back into neutral, the idle speed is 1500 rpm.

The idle speed cam is in the low position, choke fully open.
The throttle cable does not appear to be stuck.

Is it possible that when the engine is hot, the throttle shafts remain stuck due to expansion? When cold, they turn freely.

Disconnecting and plugging the vacuum line that goes to the EGR solenoid does not change anything.
I did the same thing with the vacuum behind the carburetor that goes to the MAP, the idle speed drops but the engine doesn't run smoothly and I get code 34.

Despite hours of searching on forums, I'm out of ideas.

Thanks for answers ! (sorry for my bad englis, I'm in France)

 

It sounds like you have been very thorough in all this work. This may or may not be your problem right now but the Idle Air Bleed (IAB) that has never been serviced has two O rings that almost certainly need to be replaced. These should have been supplied in your rebuild kit and brief instructions are attached here. When the cover is off the IAB can be removed with a flat blade screwdriver. It is very sensitive to adjustment so carefully count the turns when removing, change the O rings, lubricate them with transmission fluid and reinstall using the same number of turns. Good luck, Todd

 

Here is another page

 

Thanks for your answers.

I removed the IAB screw, and sure enough, the 2 O ring were dead. So I changed the O ring, but same problem.

I plugged vaccum to EGR solenoid, AIR diverter valve and EFE valve. Just keep PCV and VAC sensor vaccum.

Here is a video showing how engine behaves when it's warm

 

Well that would be frustrating. How did you adjust your mixture control solenoid when you did the carb rebuild?

 

I adjusted the solenoid with lean mixture screw and 1,304" home made gauge. I haven't touched the rich mixture stop screw, and the idle mixture screw. Plugs are still here.
For IAB, I counted turns (8 turns to remove IAB)

I tried again by plugging all the vaccum (EGR, EFE, PCV, AIR diverter valve, caniser control valve, heater, front vaccum break, brake booster) Just keep VAC vacum (I replaced the line between carb and VAC sensor)
I tightened it slighty the carb

None of that makes any difference...dwell drops10 and warm idle 1500 rpm

BUT ! when I manually choke the carb, dwell increase and idle decrease...there is definitely a vacum leak but where ????
I checked exhaust manifaild gasket, I haven't seen engine gas leak.

Maybe intake manifold gasket ? carb gasket on manifold ?

I also followed this procedure as well : all the values are correct

 

OK that all sounds good. Take a look at the attached photos and you will see a GM gauge used to measure the float height and the mixture control travel externally, sort of a dipstick to check them. With these measurements you can make your own gauge, note that the gauge lines start 1" 5/8" from the bottom of the stick. Your float height measured at the center hole with the engine idling is supposed to be 11/32. Having set the lean mixture screw while rebuilding the carb you now set the rich screw (engine off) for 4/32 travel (some say use 5/32). Hope this helps, good luck

 

Oh thanks for your help ! So tomorow, I'm going to go over all the settings again

Can I leave the two idle mixture screws at their factory settings ?

 

Yes i would, i cut mine open but seem to always come back to the original setting

 

I dissassembled the carburator, in the end, I missed a lot of settings.

First, the float level is too low :



Secondly, my gauge wasn't exactly 1.304" ; I made a new one why a inch ruler





Unfortunately, when I removed the rich mixture screw plug, I stripped the threads
Unfortunately (yes again) , I broke thread tap inside...

I have a second carburator, but the TPS screw is seized, I can't get it out