What if the Fuel pressure regulator failed...

delash_81

Well-known member
Aug 8, 2005
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43
Atlanta
What kind of symptoms would be seen from a failed or 'stuck' fuel pressure regulator, say it is stuck closed? Open?
 

R_Lefebvre

Well-known member
Dec 10, 2007
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Depends on the fuel injection system. I'm not familiar with the inner workings on the Disco yet.

Some fuel injection systems have a fuel pressure sensor which will allow the computer to know the pressure, so it can adjust injection time to compensate for the changed flow.

If there is no pressure sensor, but it's a good system, it will see the rich/lean and still be able to compensate blindly.

If it's a really crappy system... it likely will be either very rich or very lean at either the high or low end depnding on where it's stuck.

I have a Pectel injection system on a turbo Focus track car, and I can make the thing run in any condition. Right now it runs with a static fuel pressure. No manifold pressure compensation. 40psi all the time.

I've also made it run at idle with NO fuel pressure. The vacuum in the manifold "sucks" the fuel through the injectors. Just goes to show almost anything is possible.
 

delash_81

Well-known member
Aug 8, 2005
135
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43
Atlanta
Rich Idle, and as the car warms up, will stall and stumble under acceleration. When the car is at speed and warm though, it has none of the above symptoms. This is most pronounced as the car is warming up from cold and goes away once car has warmed up and been driven for a few minutes at highway speed (min 55 mph). I have been chasing this problem whenever the temps outside drop below 60 deg F. Summertime it runs fine, only in the winter/fall/spring do I see this issue.
 

delash_81

Well-known member
Aug 8, 2005
135
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43
Atlanta
I found this in the description of the SFI fuel system on the RAVE disk:

Fuel pressure regulator

The fuel pressure regulator is located at the rear of
the engine in the fuel rail. It consists of a fuel inlet,
outlet, vacuum port and internal diaphragm.
When the engine is under high manifold depression,
the applied vacuum sucks the diaphragm of its seat,
allowing fuel to return to the tank, resulting in a lower
fuel pressure. This is necessary because the high
depression will try to suck the fuel from the injector,
resulting in overfuelling if the pressure remained
constant. Failure will result in a rich mixture at idle but
normal at full load, or a rich mixture resulting in engine
flooding, or a weak mixture. Although the fault will not
illuminate the MIL, faults caused by the failure may be
indicated.


Does the same hold true for MFI System as I am seeing this type of issue. Could overall low fuel pressure from pump also give similar symptoms?

Thanks in advance

-delash
 

R_Lefebvre

Well-known member
Dec 10, 2007
942
0
Low fuel pump pressure would result in a lean condition at high power settings. You'll get power loss and/or detonation at loads.

As for this problem with running when cold, I'd suspect it was a temperature sensor fault. You're probably not getting the cold start enrichment you need. After it warms up, no longer needed, so you're fine.