Fuel pressure

Bosko5.0 · Mar 26, 2008

Is IT possible for a 5.0 to run with a fuel pressure of 30psi???

with my autometer guage thats what it reads when i rev it it increases a couple psi. should I be worried???

Its an electric full sweep I hooked the 12v for lights to the headlight switch the ground to the panel under the dash, and the 12v ign source into the defrost purple/red wire.

did I do something wrong?

Turkey Sammich · Mar 26, 2008

Well... a stock 5.0 is usually around 39PSI, 30 is pretty low.

Bosko5.0 · Mar 26, 2008

whould that affect mpg since I get like 80miles to half a tank?

Bosko5.0 · Mar 26, 2008

Well I just took it for a run and was idleing at 26psi and when I went WOT to 5k rpm it went upto 37psi then dropped back down to around 28psi.

95Vert · Mar 26, 2008

Do you have an adjustable fuel pressure regulator? If not, get one. If so, just adjust it to 39 w/o vaccuum. If it's stock, have you changed anything, ie; ignition, coil, inj, maf.... Get with Wes since you have the TwEECer, he should be able to help you out.

GTA_V6_Mustang · Mar 26, 2008

Actually that seems about fine. Mine is about 30-32 at idle and almost 40 if not 40 give or take a psi at wot. These older cars didnt require as much fuel pressure to run correctly. And With that fuel pressure my car runs just fine and am able to get 28mpg just fine. cruising I am around 34-36 psi give or take a psi lol.

HGFireHazard · Mar 26, 2008

Ya know, mine is like that too... the only problem is that I have a blower and mine doesn't go above 40 or so psi at WOT.

I idle anywhere between 29-32 psi, when I free rev it will jump to 40, and when I get into boost it still doesn't go past 40.

I know that with each psi of boost the fuel pressure has to increase 1 psi, but my gauge just doesn't show it.

Either my gauge is screwed up or I have a vacuum leak somewhere.

millhouse · Mar 27, 2008

Turkey Sammich said:
Well... a stock 5.0 is usually around 39PSI, 30 is pretty low.

39psi is read only with the vacuum line removed. If you leave it connected, I believe 30-32 psi is right where it should be. When you rev the engine it should go close to 39 psi.

95Vert · Mar 27, 2008

millhouse said:
39psi is read only with the vacuum line removed. If you leave it connected, I believe 30-32 psi is right where it should be. When you rev the engine it should go close to 39 psi.

Mine only decreases by about 3-4psi, not 7-9. So when I pull the vacuum it goes down to about 36, but not 30. If the vaccuum is on, and he's still running 30psi, then without it, it'll be in the high 20s, which is pretty low.

millhouse · Mar 27, 2008

95Vert said:
Mine only decreases by about 3-4psi, not 7-9. So when I pull the vacuum it goes down to about 36, but not 30. If the vaccuum is on, and he's still running 30psi, then without it, it'll be in the high 20s, which is pretty low.

While 30 is a tad low, if he's pulling good vacuum I can't see it being that far out of tolerance, and a 7-9psi drop is not unheard of. If the vacuum is on at 30 and he pulls the vacuum line off, it will raise up, not drop it down…which would put him into the 36-40 area which would be stock.

95Vert · Mar 27, 2008

millhouse said:
While 30 is a tad low, if he's pulling good vacuum I can't see it being that far out of tolerance, and a 7-9psi drop is not unheard of. If the vacuum is on at 30 and he pulls the vacuum line off, it will raise up, not drop it down…which would put him into the 36-40 area which would be stock.

Ja, that's right. Shows how long it's been since I've worked on my car. I need to get back in the game. But yeah, Millhouse is right.

Black95GTS · Mar 27, 2008

Bosko5.0 said:
whould that affect mpg since I get like 80miles to half a tank?

Your fuel pressure is fine, but something else is wrong if the above is true.

Adam

HISSIN50 · Mar 27, 2008

AFAIK, 30 PSI is the absolute low-spec for fuel pressure. I might check pressure with a known diagnostic gauge. Compare the two readings at the same time.

A normal scenario is to se WOT pressure at 38-39 and to see 34-35 at idle with the vac line connected [near 20" hg].

Bosko5.0 · Mar 27, 2008

When the vaccum line is disconnected fuel pressure reads 40psi.

Unfortunate Jt my sensor is hooked up at the test port.
I do see around 36-40 psi at WOT.

My vaccum stays around 19hg

And my oil pressure stays at 50psi

And my afr stays around 14.8

GTA_V6_Mustang · Mar 27, 2008

theres nothing wrong with your fuel pressure. One thing you guys have to rememer about the accuracy of your electric fuel pressure guage. Depending on how good of a ground your using depends on what that guage is going to read. 32-34 give or take is just fine at idle.

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