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Stalling problem when engine gets hot - Vapor lock? Bad fuel pump?

07-14-2017, 04:21 PM
The car is a carbureted 1985 Firebird with a mechanical fuel pump that has recently developed a stalling problem after driving it for about an hour which seems to be heat related. I believe it's vapor locking. Some backstory:

Had the car for about 2 years and never had this problem until the fuel pump went out and had to replace it. After finishing that job I took it to get some gas, filled up, and when I started the car it just went crazy, idling over 3000 RPMs. Adjusting the idle speed screw had absolutely no effect. Had it towed to a shop and they did a few things - reconnected my secondary barrels (since disconnected again as it resulted in a huge lack of horsepower and bad hesitation), adjusted ignition timing, replaced cap and rotor button (apparently had broken off). Picked it up from there and it stalled out about 9 miles in to the 11 mile trip home. I replaced the spark plugs, wires, and ignition coil.

Now, it starts up fine and will run fine for awhile but when the engine warms up it starts to occasionally dip or bog down when going 30+ mph (don't really know if that's the right word for it but basically the acceleration is not as strong or responsive as expected and feels like the car might be about to stall) and hesitates a bit when taking off from a stop. If I stop and idle in park it will idle really poorly for awhile and die. If I continue driving it will stall. If I can get it started again at that point it will run poorly for a bit and stall again. Then it won't start until it cools down. Guessing this is vapor lock - I checked the fuel lines under the car after this happened last night and they were certainly hot as hell.

Now I know correlation doesn't equal causation but I find it a bit suspicious that this started happening after replacing the fuel pump. Is it possible that a faulty fuel pump could be the cause of my vapor lock, if that is what this is? And if it is vapor lock, how can I fix it?

07-14-2017, 10:10 PM
To pin this down, you should do a pressure test of the fuel pump, make sure the filters are clean. Also if it has a Quadrajet there is a small fuel filter in carb inlet. Also may be a sock/filter in the tank.

Blue Bowtie
07-14-2017, 10:14 PM
Did you service technicians seal the main well plugs on the bottom of the carb?

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