Ok. I think I might have been having issues with vapor lock, and that caused problems with my smog test yesterday and just in general, and I want to check that you all would agree that my problem sounds like vapor lock.

Anyway, I started out with 1/2 tank of 91 octane and emissions cleaner. It was 98 outside, >100 in the sun, with a black hood (my Firebird). I ran it rather gently for ~60 miles with no problems, then hard for ~20, almost to dry in the tank.

Stopped for gas, tank was pressurized with vapor. Added 6.5 gallons of 87 to get ready for the smog test. Ran it gentle for 10 miles, hard for 40. Near the end of the hard runs, we started out for the e-test center. It died on a small hill. Wait 40 sec, prime several times (pump sounded like it was REALLY straining), and it started. Drove for 5 miles, it died again. Wait, and it started fine. Still had plenty of gas, temp about 220 when it would die. When I would re-start it, temp would be at 250+ and the coolant would often be boiling in the overflow res. Got it to e-test, let it cool for a bit, and then ran it through. It had some problems with heat and running, and I blew way worse than before, 17/3 vs 3.4/3 on hydrocarbons.

It died some more on the way back, so we stopped at Target and let it cool for 25 min. Started fine, drove fine for 8 min to a gas station. Open the tank, and it was WAY pressurized. Like many seconds of venting with the cap partially open. Fill it up the rest of the way with 87 (9 gallons) and drive away. Drives fine all the way home (5 miles) and later that night.

Every time it would die, you could hear the pump straining like nuts. Same with the priming, then it would go. It would stumble like crazy before it died, and would completely refuse to catch before it cooled some.

Sound like vapor lock?

Thanks!

 

not to me, but what do i know

 

Check your fuel pump pressure. Sounds like you might have a pump going bad, or the pick-up is plugged, or the filter is plugged. Vapor lock with the high TPI fuel pressure isn't that common.

 

i dont think iv ever had vapor lock with a pressureized system and i dont think its really possible unless its like 200 degrees out or something. Vapor lock is only something that tends to curse carb owners with their mechanical fp's that suck the gas from the tank. The decrease in pressure below atmospheric int he fuel line causes the fuel to literally boil at the lower pressure.

 

but why in the world would the problem go away once I vented the tank?

This only happens when very hot out and the tank is ~1/2 or less. Full or cool, no problems.

 

maybe your fuel tank vent line is blocked,,,you havent messed with your charcoal cannister lately have you ?

 

rileys right.. your tank isnt venting properly. very hard on the pump to pull against a high vacuum. Leave the gas cap cracked open a little and that shoudl stop it for the mean time.

 

I haven't touched the canister. But cracking it helps! Thanks!

 

gonna reopen this thread instead of starting a new one....

where is the fuel tank vent line? cuz this is happening to me too...

i lookd under the car near the tank and theres this little filter looking thing that looks pretty dirty..its just hangin there, its like..off white colour...is that the vent line?

 

That's the tank vent to let air in to replace the fuel as it's used.

 

so how would i go about replacing that? or is it just a little filter?

 

It's mostly a check valve. Should be able to figure out some sort of replacement for it. Disconnect it for now and see if your problem disappears.