I have a 1984 Pontiac Trans Am,305 cc Quadrajet.automatic transmission.
Performed basic tune up,because the car had rough idle,ran fine just seemed like it was going to stall at a stop sign. Changed,cap,rotor,plugs,wires,fuel filter,pcv valve.Did all that and car ran great,idled fine good throttle response ect.The next day my son drives 3 1/2 hours too college with no issues. He drives to class the next morning,comes out of class and car hard to start then idles up to 1500 rpm then died and would not start.Had it towed to local garage and they changed plugs,saying the bosch platnums were wrong and it also needed a carburator.I went up and got the car towed back home.Got a new rebuilt carb and installed last night.Car hard to start and backfires through carb ,stumbles then dies.changed plugs,car idled fine but as soon as you hit the gas,backfire and dies.....Not sure what to do now....need some help!

 

Did you verify timing and firing order was correct? Maybe they swapped a wire around when they were changing plugs.

 

Double checked firing order and wire locations.Thinking my AZ plug wires that are brand new might be junk......

 

Check the timing. And if the timing is correct. Double check 0 on the balancer. The outer ring can spin.

 

48,000 mile car....possible my cam is wiped? #4 plug carbon fouled,#8 same...others all good.

 

Verify timing with TDC on number one and where the dizzy is pointing. Timing chain can jump like two teeth and they will still run.

 

I checked the possibility of "timing jump" by putting a stiff wire in the spark plug hole,rotated the engine by hand,when the wire stopped moving upwards the dizzy rotor was pointing at #1 on the cap.So that being said I don't believe it "jumped timing".....I'm now leaning towards a clogged catalytic converter.Any input on this would be appreciated.Roger

 

Pull the O2 sensor and run it like that.If that solves the problem then it's the cat.

 

Got the engine to fire this morning,had it running maybe one minute. Got under car,the exhaust pipe going into cat was approx.150 degrees, the pipe coming out was 80 degrees.Cut the cat on the engine side and car fired right up,.....was completely clogged,removed the internals,welded back in place.Getting ready to fire it up.

 

Photo of whats in a bad catalytic converter....

 

Picture won't load.....working on that

 

Well,photo won't load...The photo I wanted to load shows the destroyed internals of a bad catalytic converter with 48,000 miles on it. Engine runs like it should now. New carb might have not been needed. Seems like the whole problem was the clogged converter. So many symptoms and so many possible solutions. Hopefully this thread can help someone in the future save some time and money. My symptoms were, carbon fouled spark plugs, carburetor dumping too much fuel in the engine,hard starting,rough idle,backfire through carburetor,severe miss....