Can't get my FP to go below 41

[Renthorin]

I am trying to set my FP to what the chip maker says but can't get it to go below 41.

Line on or line off it only changes by about 1 pound.

Accufab regulator and I bought a second to try - no difference.

What would be a possible cause for why I can't get it down?

 

[pacecarta]

possibly a restriction in the return line ??? , i got a dent in mine where it goes up onto the frame on the passengerside from the crossover exhast header flange when the motor rolled over (didnt have a strap). right now pressure on mine is ok but its something to look at

 

[Turbo6inKY]

Have you tried a different gauge?

 

[Renthorin]

Yup, put a new gauge (that a friend verified) on it last night and same deal.

He suggested a restricted fuel retun line so I am just checking to see if there is any other cause for this.

 

[Renthorin]

more info

well he came over to assist me and suggested I check the FP with the engine off and the pump running.

I powered the pump and with the engine off it will let me adjust the fp as low as 30.

I set it to 38 like the chip says and started it back up. Jumped to 41 and sat there even if I removed the vac line.

I put my finger to the vac line and it is sucking...hard.

So..... what does it mean when I can lower the fp if the engine is not running but not when it is?

 

[85TurboTtype]

Signs point twords return line....

When you have the car off the gas is not making a full loop. I would say that your return line is possibly kinked like the others say. Plus the vac is not there.

 

[Renthorin]

When you say "not making a full loop" what do you mean?

I know the fuel is not going through the injectors but it is still passing through the regulator and back into the tank right? I mean that part of the fuel loop as nothing to do with the engine turning over.

I would think that with the injectors not firing even more fuel is going back to the tank via the return line.

The fact that I can adjust the FP correctly with the engine off means the regulator is ok right????

 

[JDEstill]

When you say you powered the pump with the car off, you mean you applied continuous power, and the pump was running all the time? You didn't just turn the key on and have the pump go for a couple of seconds and then turn off?

If the pump was running continuously with the engine off, I can't think of any good reason why you can adjust it with engine off but not with the engine on.

It does sound like some kind of restriction in the return line though. That or a restriction in the regulator itself are the only things that come to mind.

John

 

[Mike Licht]

what fuel pump are you using. Are you using some sort of volt booster?
Mike

 

[Ormand]

When the engine is not running, the pump is getting less voltage than when the engine is running. That may explain why you can adjust the pressure with the engine off. If the restriction in the return line limits the low pressure to 40 or 41, then connecting the vacuum/pressure line can't lower it any more. Try disconnecting the return line at the front of the engine, and running a piece of hose to a gas can. If that will let pressure go lower, then you know the return line is restricted. Might be something as simple as a piece of "o" ring hung up in the line, that you could blow out by using an air gun from the back of the car, a "reverse flush" of the return line.

 

[Renthorin]

Ormand - that is exactly what I was telling my wife I need to do on the way in this morning It seems the only way to be able to confirm or rule out a blocked return line.

Mike - I have a hotwired Red's XP. I do have a volt booster but it doesn't kick in until 10 psi of boost so it shouldn't be a factor in this.

JD - I powered the pump from the wire behind the alt so it was running the entire time I was messing around.

I will try putting on a 'home made' return line and see what happens.

I did look at as much of the return as I could see last night and it looks fine....but I don't know that I didn't mess it up where it threads into the regulator.

Oh, while I was out messing with it last night a mouse came out of the radiator area and ran around the throttle body area and over the headers a bit. He kept popping up to see what I was doing. Little bastards..........

 

[DavzGN]

Originally posted by Renthorin
I do have a volt booster but it doesn't kick in until 10 psi of boost so it shouldn't be a factor in this.

..........

Another thing to check is that the Volt booster is working correctly. Sometimes they go bad and full field the Alternator which will cause your pump to get ~16V even at idle.

HTH
David

 

[Renthorin]

well.... the only way I know the VB is working is at night when I nail the gas.....after a little boost (10ish) the lights get really bright.

Then when I let off... they go back down to normal.

I assume that means it isn't full fielding most of the time.

I guess I could disconnect it and see if that makes a difference.

 

[Renthorin]

well.......

I removed the return line and put a 90 degree elbow there and connected some clear hose. Ran the hose into a gas gan and fired the car up. FP was 35 ish so I guess the retun is clogged or dented. I will have the car up on a hoist in a week or so so I will check it then.

Thanks for everyone's help.