I have another fuel pressure question. I have a 94, 6 speed, mostly stock, 29000 miles, with an aftermarket fuel pressure regulator. My pressure is set at 42# when at idle. When I cut off the switch it immediately dropped from 42 to 24. It went from 24 to 0 in 10 minutes. I reinstalled my stock fuel pressure regulator and it held the pressure much better, but still did something weird. It shows 38 at idle and drops immediate to 34 when I cut the engine off. It slowly dropped to 30 in the next 10 minutes, but then started climbing again. 10 minutes later (20 after it was cut off) it was showing 36. It finally stopped at almost 38 an hour after the engine was cut off. From there it slowly dropped and was at 10 an hour later, which was 2 hours after I cut the engine off. I have a few questions….. Is it normal for the pressure to drop and then increase with the engine cut off? If so, what causes this? Also, apparently the adjustable pressure regulator is leaking. There is a vacuum hose that fits tight on the end of the factory regulator, but fits loosely on the adjustable one. Could that have anything to do with the pressure dropping so fast on the adjustable regulator? What function does the vacuum hose provide? The car performs much better with the adjustable regulator; will it hurt anything to run it? Lot of questions, but I appreciate the help.

 

Correct me if I'm wrong, but the vacuum line will decrease the fuel pressure.

I'm having big problems with my vette right now, mostly because I don't know the answers.

My fuel pressure would go up to 40 psi with the fuel pump priming, then drop down immediately to 30 psi and stay there forever. I loosened the gas cap, and then it dropped to zero.

As far as it increasing, the only explanation, is that the gas is heating up, and the vapors are expanding in the tank. Did the outside temperature rise? I can park my vette in a cold garage at 0 psi pressure, and in the afternoon, the fuel pressure guage will show 30 psi.

The fuel system is completely sealed. Under no circumstances should vapors escape, so pressure WILL build up in the system. Try loosening your gas cap and seeing if this vents the pressure. The cap must be off to properly diagnose fuel problems.


[Modified by CentralCoaster, 2:21 AM 8/14/2003]

 

The car was in the garage on a cold engine. I only ran it long enough to build pressure, approximately 30 seconds. It was at night, so the temp was about 80 degrees.