inconsistent fuel pressure - HELP

[Jeep-Power]

Help please.

I have a OBD1 fuel system on my turbo'd Jeep engine.

I have tried three different fuel pressure regulators - 1 brand new, one used, and one HESCO adjustable.

The trouble is that the fuel pressure will not stay fixed. What I mean is that the range between vacuum & non-vacuum still functions fine (factory is about a 8PSI difference 31psi w/vac, 39psi wo/ vac). All the regulators maintain the 8PSI difference, but the base pressure changes almost every time I shut off & restart the engine. The low pressure (w/vac) reading can be as low as 25psi and as high as 40psi. As you can imagine, this does not make the thing run well-- either too rich (stinky) or too lean (not what you want with boost!!)

I am running the OEM fuel rail with 47lb Ford injectors, 3/8" fuel & return line, and a Aeromotive 340 Stealth in-tank pump (brand new with less than 1000 miles)

has anyone else had this issue?

[atias]

try to check the voltage to the pump when the engine is running. maybe your having some power issuses , i had this problem with the stock powerline to the pump that was thin and weak.

[cruiser54]

Ground for the fuel pump is behind the trim panel that the spare tire fastens up against. Possibly add a ground from the fuel pump module as a dedicated ground?

[Jeep-Power]

thanks for the leads-

I do have a designated 12ga wire running to the pump w/a 12ga ground. I will double check all of that.

Another puzzling piece is that the offset will hold-- I drove it 200 miles and the pressure stayed the same. Shut it off to get gas and then on restart it was different. Is there anything mechanical that might cause this?

[atias]

when the engine is cold is it on the high side of the fuel pressure ? and when the engine is hot then the fuel pressure taking a dive?
if so maybe the fuel is boiling and you get some kind of vapor lock in the system then the pressure goes down until the fuel gets cold again.

[Jeep-Power]

Hey folks- Still having this issue. With some more seat/drive time, I have been able to figure it out a little. I finally got settled in our new place (Fort Mill, SC) and have some time to tinker with it.

when the engine is cold is it on the high side of the fuel pressure ? and when the engine is hot then the fuel pressure taking a dive?
if so maybe the fuel is boiling and you get some kind of vapor lock in the system then the pressure goes down until the fuel gets cold again.

Temperature seems to have no effect on it.

The voltage & wiring are great.

the symptoms: SOMETIMES, on startup, it will begin at 20PSI with vac, and of course the thing idles like crap and is super lean (16 - 17 to 1 AFR)

It will run ok (not pop or stutter), and then with a little run time and boost, the problem goes away. It might come back again, if I shut it off, it might not. If it does, a little driving makes it go away.



I am most certain it has something to do with 3 things: the fuel pressure regulator, the high output of this pump (Accel Stealth), and boost/vacuum being applied to the regulator.

If it is the regulator being overpowered in some way and closing it down? I have checked, replaced, upgraded, and flitted with the regulars O-rings, thinking that the pump was overpowering the seal they make, with little success. However I did get some worse results (MUCH higher pressure) with leaking O-rings. So the problem of the pressure going too high seems to have gone away with the new regulator and O-rings.


Is there an external/aftermarket regulator that any of you are using with success? Again, this is an OBD1 fuel rail, with the regulator on the rail. I am looking for something that will work/integrate easily with the OEM fuel rail, if possible.


Help.

[Jeep-Power]

Bump-

still fighting this. I am going with the 'compact' Aeromotive bypass regulator-

The plan is to remove the small o-ring on the OEM regulator and plum the Aeromotive in to the return line. I hope to get it in later this week.

I am fairly certain it has to do with the Aeromotive pump overrunning the OEM regulator. This pump puts out about twice the volume the OEM pump does.

I noticed this fuel pressure issue was even worse once I unblocked a choke I had in the tank, before the pump. The pump was being limited with my initial setup. When I unblocked it, there was NO fuel pressure. The Aeromotive pump was suddenly blowing the fuel right by the old/hard/cracked small O-ring int he OEM regulator. A new o-ring helped bring it back up, but the pressure regulation issue was intensified. A series of larger, different, multiple O-ring configurations seemed to help temporarily, but noting has put it to rest.

[Jeep-Power]

the Aeromotive regulator definitely helps, but the pressure still fluctuates. As suggested by others, it does seem to also have something (but not everything, because it will still fluctuate with full voltage) to do with the voltage, which I guess is inevitable (like running with the lights, heat, wipers, and radio on, the voltage is gonna drop)

The pressure fluctuation seems to be bearable, because I set the pressure level higher than the OEM setting. It is set to somewhere around 48lbs without vacuum. This way, if it drops 10 lbs, the base pressure is still in the high 30's, vs it being in the low 20's with the OEM regulator.

The key thing to remember is to remove both the inner (small) O-ring & spacer from the tip of the regulator. This allows fuel to flow easily around the OEM regulator and not allow pressure to build.

The setup for now. Once I get my shop back, this will have a better mount and/or location.