Fuel pressure question

Crock · May 27, 2010

I am trying to track down a hard cold start condition I am having. Its all stock except for a 190lph fuel pump I put in last year. The condition existed before and after the pump. I replaced it because it was really loud and thought I would fix it before it died. I just put a rail mount fuel pressure gauge and noticed that if I turn the key forward it will go to about 20 psi. If I turn it forward and back a few times it will go up to 30 something. If I don't start it the pressure goes back to 0 within a few minutes. I was pretty sure that on my old fox it held the pressure for a day or days....does this sound right or does it going down after a few minutes normal? If it is not right does it mean the the injectors could be leaking? Any chance it could be the fuel pressure regulator? And my last question is about the check valve in the fuel tank. Is it in the pump it self or the sending unit assembly? Thanks for the help!

RIO5.0 · May 27, 2010

Usually a new pump will solve that issue and last a tad longer than a year before getting weak and not holding pressure...how old is the regulator on the fuel rail???
bleeding off the quick isn't normal... should hang for an hour or so then bleed off.

Crock · May 27, 2010

So the check valve is in the pump. I wasn't sure and didn't want to have to drop the tank if I didn't have to.Btw the pump only has about 3000 miles on it. The injectors and fpr are org. from 95. I read somewhere you can check the injectors by taking the upper intake off and lifting the injector rail with the injectors in it and priming the system and see if any are leaking,but I would think the pressure could shoot the injector from the rail.....any opinions on that?

toyman · May 27, 2010

I'm more inclined to think the problem lies in the FPR. KOEO pressure should be between 35 - 40 psi as soon as the pump primes. Not saying it isn't the pump but the odds are it's the FPR leaking back into the return line. Leaking injectors would not explain why the initial pressure is only 20 psi.

Crock · May 28, 2010

toyman said:
I'm more inclined to think the problem lies in the FPR. KOEO pressure should be between 35 - 40 psi as soon as the pump primes. Not saying it isn't the pump but the odds are it's the FPR leaking back into the return line. Leaking injectors would not explain why the initial pressure is only 20 psi.

Just tried it again and with koeo the pump kicks on for a few seconds and it goes to twenty. If I turn the key off and on a few times without starting it will go to thirty. After about 2-3 min its down to 20 psi and back to zero after 10 min. I am going to get a known working fpr this weekend and give it a try.

HISSIN50 · May 28, 2010

One can carefully use fuel line pliers on the return line to determine if it's the FPR or not.

Daves94vert · May 28, 2010

your diaphram in your regulator went south. Get yourself a kirban and you'll be fine.

HISSIN50 · May 28, 2010

Daves94vert said:
your diaphram in your regulator went south. Get yourself a kirban and you'll be fine.

How would one know that?

Crock · May 28, 2010

HISSIN50 said:
One can carefully use fuel line pliers on the return line to determine if it's the FPR or not.

Can you explain please? I don't have fuel line pliers,but I do have those plastic things to disconnect the line spring lock.

HISSIN50 · May 28, 2010

Fuel injection fuel line crimpers can allow you to deadhead the fuel system. If you crimp the return line and you instantly get full fuel pressure when the pump primes, you know the FPR is likely causing the bleed down.

Crock · May 28, 2010

I bought a set of used injectors and a stock FPR from a local guy. I only changed the fpr and now my pressure after a single prime is at 30 psi instead of 20. Is this where it should be or does it need to be higher? Should I go ahead and change the injectors or whould that be a waste of time?

Thanks for all the advice so far guys!!

While running and vac hose off it is at about 38-39. I will try and cold start in the morning and see if the 10 psi boost helps.

toyman · May 29, 2010

You are closer to spec now. KOEO 39-45 psi. KOER 35-40 psi with the vacuum line connected. Try clamping the return line. The pressure should go above 70 psi.

Crock · May 29, 2010

WTH!!! This morning I tried a single koeo then checked the pressure and it was at 15. Last night it went to thirty,but it wasn't a true cold start. I primed it a few times and it went to thirty. The holley pump I put on a about a year ago only has 1 to 2 thousand miles on it and the hard start problem was there before and after. Could it be the pump? I doubt I would get warranty on it. Would a stuck injector cause this? I know in a fox the fuel pump relay is under the driver seat,where is it in a sn95? Man,I am getting so frustrated with this car that I hardly driven it in the last year.

The one right next to the schrader valve is the return?

KamiKaziDK · May 29, 2010

Other than your gauge reading lower fuel pressure....what's the car actually doing?

Crock · May 29, 2010

It cranks for about 3-5 seconds before it starts unless it has run in last few minutes.

Daves94vert · May 29, 2010

was it a stock used regulator?

Crock · May 29, 2010

Yes...I was told it came off car running and that he only took it off to upgrade.

Crock · May 29, 2010

Checked the voltage at the inertia switch and it was 10.2 volts. Normal?

HISSIN50 · May 29, 2010

toyman · May 30, 2010

Crock said:
Checked the voltage at the inertia switch and it was 10.2 volts. Normal?

I would check the voltage across the battery (reference) and from the battery positive to chassis. If the latter is lower I would suspect bad ground(s). Low voltage will affect fuel pump output.

Fuel pressure question

Crock

Member

RIO5.0

Crock

Member

toyman

Crock

Member

HISSIN50

"How long does it take to get help in here?

Daves94vert

HISSIN50

"How long does it take to get help in here?

Crock

Member

HISSIN50

"How long does it take to get help in here?

Crock

Member

toyman

Crock

Member

KamiKaziDK

Member

Crock

Member

Daves94vert

Crock

Member

Crock

Member

HISSIN50

"How long does it take to get help in here?

toyman

Similar threads

Fuel pressure question

Member

Member

Member

"How long does it take to get help in here?

"How long does it take to get help in here?

Member

"How long does it take to get help in here?

Member

Member

Member

Member

Member

Member

"How long does it take to get help in here?

Similar threads

Privacy & Transparency

Privacy & Transparency