Fuel Pressure Questions

sts70004

Registered User
I've been having a problem starting my car recently. The first time it starts, it usually idles like crap and dies. Then when I try to start it again, it acts like nothing was wrong. So I checked a bunch of sensors, all good, and now I just tested fuel pressure at the rail. Here's what I got:

Key On Engine Off: 0-psi

Key On Engine Running: 32psi, does rise and fall with vac/boost.

Should I be getting pressure with the engine off but the key on?
 
I've been having a problem starting my car recently. The first time it starts, it usually idles like crap and dies. Then when I try to start it again, it acts like nothing was wrong. So I checked a bunch of sensors, all good, and now I just tested fuel pressure at the rail. Here's what I got:

Key On Engine Off: 0-psi

Key On Engine Running: 32psi, does rise and fall with vac/boost.

Should I be getting pressure with the engine off but the key on?

Sounds like the fuel pump is bleeding pressure down after you shut it off. Yes you should see fuel pressure when you turn the key on, without the engine running. If it immediately bleeds down after the 15 sec run cycle, your pump is on its way out. Next time you attempt a cold start, cycle the key to on without starting,then cycle it off and try to start. If it starts normally, I would plan on changing your fuel pump soon.
 
Sounds like the fuel pump is bleeding pressure down after you shut it off. Yes you should see fuel pressure when you turn the key on, without the engine running. If it immediately bleeds down after the 15 sec run cycle, your pump is on its way out. Next time you attempt a cold start, cycle the key to on without starting,then cycle it off and try to start. If it starts normally, I would plan on changing your fuel pump soon.

The fuel pump has only one relay right? The one in the trunk? The person at autozone thought maybe there were two, one that was responsible for the initial build of pressure, and one for running the pump continuously. I thought that was unlikely but i didn't argue the point. Also, the pressure did not shoot up quickly to 32 psi during the test. It built kind of slowly. Fuel pump probably shot?
 
These are standard tests that the system runs when reading codes.

If you own an SC, you should own a code reader or at least go to the nearest auto parts store that will pull them for you.
 
Well I just replaced the fuel filter recently. So you'd recommend fuel pressure regulator? Is there any way to test this?
 
Well I just replaced the fuel filter recently. So you'd recommend fuel pressure regulator? Is there any way to test this?

Start by pulling the vacuum hose off the regulator to see if fuel is getting into the hose when the pump is running. Ground this lead of the EEC test port to keep the fuel pump running with motor off and ignition on. With a fully charged battery you should see 38-41 PSI (motor off).

fuel%20pump%20test.gif


David
 
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So i went ahead and did that test, and I got 40psi with the engine off, and I figured, with the fuel system primed, i'd try to start the car. Well it didn't really help, still the idle was like crap and my fuel pressure went from 30-40 psi with the idle(when the idle dropped really low, vacuum went down) and it just kept doing that until I gave it throttle, at which point it settled down and idled fine. Into boost, fuel pressure went up to 50psi, at idle 30psi. When I shut the engine down it read 38psi, engine off, sitting for 5 minutes, it still read 38psi. Its now been sitting 20 minutes, and it reads 27psi. Any ideas? Injectors maybe?
 
Oh in addition to the above post, been over an hour now, 0 psi on the fuel rail.

Pressure readings sound normal. Did you get a chance to pull the vacuum hose off the regulator, to verify you aren't getting any fuel leaking through the hose ?

David
 
Pressure readings sound normal. Did you get a chance to pull the vacuum hose off the regulator, to verify you aren't getting any fuel leaking through the hose ?

David

Well I wasn't sure what to look for when I pulled the hose off. It smelled kinda like gas if I got the end of the hose right up to my nose, but not strong. I had the pump run continuously for 5 minutes while watching the top of the FPR, and no fuel. Oh and I redid my KOEO fuel test, turns out the fuel pressure gauge I was using was slow, or it didn't seat fully, cause the pressure jumped up to 40 psi when I turned the key. I'm beginning to think fuel system is fine and the bug is somewhere else... I guess I'll clean the IAC?
 
Update!

I think its the IAC. I took it off and it was super dirty and when I cleaned it with lots of throttle body cleaner, it definitely was an improvement. But then... The goose sound... Now it also idles really high no matter what I do :( oh well, time for a new one. Hopefully when I get that swapped my starting problem goes away hehe. Learned a lot about the fuel system though :rolleyes:
 
I think its the IAC. I took it off and it was super dirty and when I cleaned it with lots of throttle body cleaner, it definitely was an improvement. But then... The goose sound... Now it also idles really high no matter what I do :( oh well, time for a new one. Hopefully when I get that swapped my starting problem goes away hehe. Learned a lot about the fuel system though :rolleyes:

Buy the IAC valve from Ford (and a new gasket)...the aftermarket ones don't usually work.

David
 
Oh oops. I already bought it before I checked this thread. It appears to be working alright though for now... Oh also... It appears a vacuum leak was present, but only under certain conditions. The collar nut on the top was a little loose, and when I would start the car, it would leak, but as soon as the throttle was blipped it would seat and not leak (noticeably, like <1-2 inHg) anymore. That would explain the starting problem too. I think it was a combination of both though.
 
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