I've been having a problem lately and can't seem to find out what exactly it is. I've been searching forever and don't see anything to my help. When I take off in first gear it stumbles and backfires up until about 2500rpms, then it starts to clear out. I tested my fuel pressure and its at 46psi when running, but when I turn the key off, the pressure drops to about 3psi in about 4 seconds. I heard to can test whether the fuel pump return valve or whatever it is is faulty or if its the pressure regulator. Anyone have an ideas. Thanks,
Brandon

 

https://www.thirdgen.org/techbb2/sho...turn+line+drop

 

OK, so I capped off the return line and pressurized the system. The pressure dropped, but not half as bad as before. It's about 10psi per 20 minutes or so. So, according to other posts it seems as though the regulator may be bad? Am I correct or not. Anything else you think i should do before i replace the reg. It's the cheapest thing to anyways. Thanks for the reply

 

If you've only lost 10 PSIG in 20 minutes of shutdown, the loss is somewhat normal as fuel seeps back through the pump checks.

Basically, you've proven that the injectors are not leaking down (at least not significantly) and that the regulator is probably leaking fuel back to the tank. If the system maintains adequate presure at WOT for any duration, you can just ignore it. If the pressure begins to drop under WOT use, you need to repair the regulator or risk going lean under heavy load (not a good thing at all).

 

The pressure at idle or WOT stays the same, but when you are low in the rpm range such as idle to 2000, it backfires and misses unless your are at WOT then it is just fine. Would it then be the regulator? Thanks for the replies

 

If I understand you correctly, the vacuum at the FPR is having no effect on fuel rail pressure. If that's the case, you need to repair the regulator. Before you dive right in, make sure you have vacuum at the FPR at idle.