fuel pressure regulator

[richmobj]

 my fuel pressure dies off when the car is shut off for a few minutes and it takes a long time to start. is the adjustable fuel pressure regulator supposed to hold pressure in the line?

[PacecarTA]

its supposed to
could be losing quick due to a bad regulator or
 a leak before the regulator ,
leaking injector or injector o ring
, leaking lines  or
could be in the tank leaking at the hose from pump or even a bad check valve in the pump

pump should prime for a few seconds when key is turned to run position   and should eb enough to build pressure , if it doesnt prime check the fuel relay on passenger fender


what pump do you have?

[richmobj]

I just purchased and installed an entire new fuel system from turbotweak.com including the Walbro 255L/hr pump, accufab fuel pressure regulator, TT chip and matching 42 lb injectors and hotwire kit.  I also have a fuel pressure gauge installed at the fuel rail schrader valve. 

I've read that the pump should turn on for 2 seconds when the key is switched to the on position.  Either the pump isn't priming or it isn't priming enough to register on the fuel rail because the fuel lines are completely empty. 

I have the pressure set correctly (43 psi hose off, 38 psi hose on at idle).  When I shut the car off, the pressure keeps dropping until it goes away completely in about 30 minutes.  Then when I go to start it, I have to crank it for a good 10 - 15 seconds before the fuel pressure gauge jumps strait to around 38-40 and the engine fires right up and runs fine. 

I performed the troubleshootin g procedure that has you pinch off the fuel inlet soft line right after shutting off the engine while watching the fuel pressure.  The fuel pressure still drained off.  Then I pinched off the fuel return line after shutting off the engine.  The pressure didn't bleed off at all when I did that.  The troubleshootin g procedure said that means that the fuel pressure regulator is faulty.  I then called Acufab and the tech support guy told me that the adjustable fuel pressure regulators aren't supposed to hold fuel pressure after the engine is turned off and the pump stops pumping.  That didn't sound right to me.  After performing the troubleshootin g procedure that I performed, I'm pretty sure that tells me that the fuel injectors aren't leaking and the fuel pressure is going away by escaping past the fuel pressure regulator into the fuel rail and back into the tank which equals a bad regulator. 

The thing that confuses me is how the fuel pressure gauge is supposed to read a pressure after the engine is shut off if it's down stream from the fuel pressure regulator in the fuel rail.  I guess my question is, should the fuel rail be pressurized with the car off or should it all drain into the tank and the pressure is all held between the regulator and the pump?  If the fuel rail is supposed to be pressurized while the engine is off, what holds the pressure there?

[earlbrown]

There's a check valve in the pump. The regulator is actually after the gauge. The fuel enters the injector rail on the passenger side, hit's the regulator and it lets extra PSI's go back to the tank. Are you sure what you thought was the feed line wasn't the return line?

It sounds like you're not getting a prime signal and you're having to wait until the oil pressure back up takes over and fires up the fuel pump. Does your oil light always go out before the engine starts?

When you did your pump, did you put a piece of fuel hose between the pump and hanger or reuse that push-on pulsator?

[richmobj]

Oh, that clears things up a bit.  I was thinking it was backwards.  So the inlet to the fuel rail is on the passenger side.  that means that i was pinching off the outlet when I thought that I was pinching off the inlet.  So the pressure held when I was pinching off the inlet and not the outlet and it's the inlet that was leaking back into the tank.  So the pump isn't holding the pressure when the engine is off.  I did take off the pulsator thing and replaced it with the hose that came in the kit so I don;'t know why it would be holding pressure unless it's just a bad check valve inside it.  So do you think that it's the fuel pump or the relay that controls the prime signal because that makes sense too.  The fuel pressure gauge doesn't move at all until i crank it for 10-15 agonizing seconds. 

[PacecarTA]

on the 15 second .. you need a fuel pressure relay

and 30 minutes isnt an issue , with fresh rubber lines it only takes a couple drops to do that 

and no the regulator doesnt have to hold 100% to still do its job , when off its its just a metal disc sitting on top of a metal tube , no rubber so it can bleed down

[richmobj]

I'll check the relay tomorrow.  that would be the easiest fix of all.  Do they sell those at autozone or advance auto?

[earlbrown]

I hate to be overly simplistic....      but have you checked the wiring like where the plug attaches to the fuel pump relay?  I'm sure it's happened but I've never heard of one going bad.

http://ihadav8.com/forum/VortexBuicks/fuel_pump.htm

[richmobj]

turns out it was the ECM of all things.  The only way that I can explain it going bad is when I installed the hotwire kit, i routed the alternator wire poorly and it touched the hot exhaust manifold and melted the insulation off and probably shorted to ground for a second.  That must have messed with the ECM some how.  Luckily, I had replaced it in the last couple months from Advance Auto and they gave me a new one under warranty.  now I am getting the prime signal for 2 seconds and the car starts right up when I crank it. 

[SuperSix]

turns out it was the ECM of all things.  The only way that I can explain it going bad is when I installed the hotwire kit, i routed the alternator wire poorly and it touched the hot exhaust manifold and melted the insulation off and probably shorted to ground for a second.  That must have messed with the ECM some how.  Luckily, I had replaced it in the last couple months from Advance Auto and they gave me a new one under warranty.  now I am getting the prime signal for 2 seconds and the car starts right up when I crank it. 

Cool! Glad you got it fixed.