Fuel pressure problem

[FE3X CLONE]

On an EFI engine, what would keep it from holding fuel pressure?

I'm having an issue with mine lately on the 455. Been trying to get it fired back up since I had it running last fall and its been pretty rough going.

I think one of my problems is fuel pressure. When I turn the key, I hear the fuel pump turn on and run for 2 seconds like its suppose to. However when I go to the passenger side of the car to check the fuel pressure, I can see it dropping really fast back to zero.

I checked for leaks and tightened all my fittings and everything seems good. In fact, last fall I had a few leaks in the system but it would never lose pressure as quickly as it is now. Would take it at least 10-20 minutes for it to drop back to zero.

Fuel pump is obviously working as I can hear it and have confirmed I have fuel pressure at the rails. So what's left? Fuel pressure regulator? It's brand new and was working fine last fall. What would cause it to fail all of a sudden?

Thanks for the help,

 

[Blake442]

I'd start with the fuel pressure regulator first.

Is it vacuum actuated? Maybe the line to it has been torn/cracked.
It could also have just gone bad... Not as likely, but it's possible.

 

[FE3X CLONE]

It's a boost referenced fuel pressure regulator but I was told you should still hook a vacuum line to it on a NA car because it still helps with the fuel regulation.

The vacuum line going to the regulator is brand new. Just installed it a few weeks ago.

 

[megaladon6]

there's usually a check ball in the pump/pickup that prevents the fuel from flowing backwards (and dumping pressure) after the pump shuts off.
best advice is get a buddy to watch the gauge, and to hook a hand op vac pump to the regulator and see if applying certain amounts of vac make a difference.
do you have a supercharger?
also, do a volume test. i've often seen good pressure and poor volume.
what do your plugs look like?

 

[86Cutlass383SR]

Andrew, I'm not really up on the type of regulator you're using but I do know that on a TPI type regulator, the regulator diaphram itself can also cause that. Even if the vacuum going to it is new, the diaphram could be letting fuel leak past it back to the tank.

 

[FE3X CLONE]

there's usually a check ball in the pump/pickup that prevents the fuel from flowing backwards (and dumping pressure) after the pump shuts off.
best advice is get a buddy to watch the gauge, and to hook a hand op vac pump to the regulator and see if applying certain amounts of vac make a difference.

I'll give that a try.

do you have a supercharger?

No.

what do your plugs look like?

I haven't pulled them back out yet to check. Mainly because I'm still trying to get the cranking pulse widths dialed in so that it starts correctly. I've been told that a bad check valve or regulator would cause to take longer to start but shouldn't necessarily keep it from running.
The problem is that I'm starting from scratch with my EFI tuning, so it's hard to tell whether its the fact that the fuel pressure isn't right causing the hard starting, or if its still my cranking pulse widths are way off.
Of course I think my other issue is that for some reason my EFI computer isn't getting a tach signal which is keeping it from startin gall together. But that's another issue for another day.

Thanks,

 

[megaladon6]

are you sure a boost referenced regulator will work w/out boost? i know it'll be fine at idle, but everywhere else...
IIRC most EFI systems don't use the cam/tach signal for start upo but go off of the crank trigger only.
what EFI are you using? and what type of pump/pickup, ignition etc?

 

[jrm81bu]

are you sure a boost referenced regulator will work w/out boost? i know it'll be fine at idle, but

It should, all a boost referenced regulator does is allow more pressure when it "sees" boost. If it doesn't see any boost then it will act just like a regular regulator.

Man there's is a lot of "r's" in this post.

 

[86Cutlass383SR]

Good thing you're not talking to Elmer Fudd...

 

[FE3X CLONE]

are you sure a boost referenced regulator will work w/out boost? i know it'll be fine at idle, but everywhere else...

I was told you still want to hook it up on a NA car because it helps to dampen the harmonics in the fuel rails when each injector opens. Or something to that effect.

IIRC most EFI systems don't use the cam/tach signal for start upo but go off of the crank trigger only.
what EFI are you using? and what type of pump/pickup, ignition etc?

Well, since this is an Olds that I'm adapting EFI to, it doesn't have a crank trigger. You have to use the tach lead off the distributor to provide a signal.
I'm using the Megasquirt MS-1 in a v2.2 case. It essentially has about everything you want just short of SEFI and a few other little things. Has IAC control, fuel and ignition control, etc. But I haven't hooked the ignition part of it up yet.
Fuel pump is a Walbro 340 255lph in a Buick GN tank along with a Racetronix Hotwire setup. Ignition right now is a spare Pertronix HEI vacuum distributor. I'm trying to get the engine tuned and driveable on just the fuel side before I install the 307 CCC distributor to control the timing.