1985 pontiac trans am
5.0 carb
it start when i drive about 35 miles of highway driving and when i get in the city it stalls when im coming to a stop or when im turning.i replace the distributor cap rotor and ignition madule and it still happens.

when it stalls out i usually hard to start/or wont start but will crank over.
i usually wait like 5 mins and it will start up .
any ideas ?????????

 

does this car have an EGR valve?

 

nope .btw it has a quadrajet carb. could the ignition coil get hot and just cut it out????

 

it might. next time it does it check for spark. is it the orig. carb? reman? the more details i have the easier it would be to help.

 

nope the previous owner converted it from FI to carb. the qjet came off a 77 chevy.
i suppose the distributor is original for the fact ,when i had to replace the ignition module ,i went to autozone the ignition module for a FI is 2 prongs on each side ,when the carb ignition module had 6 on one side and 2 on the other. i had to get the FI one for my distributor.

im only 15-16 vacuum too!
could iT carb problems

 

Sounds more like a float or vapor lock issue with the carb. Does it sart right back up after stalling or lots of cranking?

 

it would stall then it would just crank not start.i waited like 5-10 min on the side of the road then it started right up.

Extra info:its has one of those inline electric fuel pumps for carb application.
my friend said vacuum to the carb or something like that.

 

if that vac reading is on a car ideling @ a normal RPM then that is too low.wouldn't hurt to check for vac leaks.

as 85FBTranam said, it may be a float hanging up or it may be vapor locking.

where is your electric pump located on the car and do you know how many P.S.I. it puts out?

 

The fuel pump is located in front of the rear tires driver side.i will measure the psi when I get off work.what causes vapor lock???
Just the other day the ground on my electric fan was getting a bad connecting and it would turn off and on . I fixed it .but can the electric fan effect it at all?

 

My fuel pressure is 6 psi !

 

thats fine for a carb

 

ok it doing it again .it only happen when it running for a long time.it smells like gas when it stalls out !

 

is your engine temp OK?

 

Yes

 

Return line hooked up?

Vac @ idle should be 22psi or so with factory settings. Your vac results lead me to belive you have a vaccum leak. Cap off all of the ports on the carburetor and intake except for one (brake booster for example) and pull a vacuum reading. If you are still at 16 PSI, then the leak is either internal to the carb or on your intake somewhere.

If the vacuum reading is 20-25, then start hooking your vacuum lines up one at a time and take a new reading each time. This should give you a good idea on where your leak is at.

The vacuum on my 355 is 16" on the gauge. Bigger cam, lopey idle etc. I had to rebuild my CC Qjet to accomodate the lower vaccum signal on the idle circuits. Bump your RPM a bit at idle and see if that fixes your problem because that's what I had to do until I got my carb rebuilt to handle the lower vacuum. However, your car is factory, mostlly, so I wouldn't think tha'ts your issue. Check the vacuum by checking the ports.

 

Electric pump with carb can cause problems. The mechanical pump will go into stall when the outlet is shut off by the carb's float valve. Electric pump doesn't shut off even when float valve closes. If the float valve isn't in good condition, the electric pump may be pushing fuel past the valve. Operate the pump with the engine off and see if fuel backs up out of the bowl vent. If so, you will need to remove the top of the carb and replace the float valve. You may also want to replace the float if it's swelled/deformed from old age. A fuel filter with a vapor return that allows pressure to relieve will also help.

 

Could it also be a bad ignition coil . I notice that when I was messing with my distributor that the top of my distributor was hot AF. My machanic said its suppose to warm not hot that you can't hold it.

 

can you show me a website of one of these fuel filters???

 

Vapor lock happens when the fuel boils inside the lines, either from engine temp or hot outside temps. IT causes air bubbles in teh line. When your mechanical pumps which pulls fuel from the tank from teh front of the car, hits one of thos air bubbles, it is unable to pull any more fuel beause ti's literally "sucking air".

This is why there was a dealer installed electric pusher pump that ran about 2PSI in the tank in many of the early 80's models. Since that pump pushes fuel out of the tank, it avoids the whole vapor lock issues because the carb would get new fuel long before the carb ran out of fuel in it's bowls.

Since you have an inline electric pump, this is not your issue.

You still need to check your vacuum with all the ports on the carb plugged off. This will tell you if you have a vacuum leak.

 

can you show me a website of one of these fuel filters with a vapor return???

 

You need an adjustable regulator with a bypass return likea mallory 4309. Have it adjusted so your fuel pressure is a constant 5.5. Hook it's return up to your factory return line. One line in, one line to your carb, the other return. This is how the factory mechanical pump was set up.

I personally have never seen a "fuel filter with vapor return" but I won't say they don't exist.

 

Well im getting my qjet over haul this Thursday , so I'll get back with y'all when I get it put on.

 

The regulator with a return line is the best setup. The fuel filter with vapor return is a quick fix for engines suffering vapor lock. The vapor line will also allow excess pressure to bypass to an extent. I have used it once or twice on engines where electric pumps were used with a carb. You can find these filters at NAPA by asking for them.