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Old 01-24-2008, 02:02 AM   #1
delash_81
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Question What if the Fuel pressure regulator failed...

What kind of symptoms would be seen from a failed or 'stuck' fuel pressure regulator, say it is stuck closed? Open?
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Old 01-24-2008, 10:00 AM   #2
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Default Re: What if the Fuel pressure regulator failed...

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.
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Old 01-24-2008, 12:07 PM   #3
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Default Re: What if the Fuel pressure regulator failed...

It will either allow you to run lean or rich, depending upon the failure mode. If the diaphragm is compromised, it can flood the plenum with fuel.

What conditions have you encountered that are leading you to believe your fuel pressure regulator has failed?
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Old 01-24-2008, 12:54 PM   #4
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Default Re: What if the Fuel pressure regulator failed...

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.
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Old 01-24-2008, 12:59 PM   #5
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Default Re: What if the Fuel pressure regulator failed...

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
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Old 01-24-2008, 01:07 PM   #6
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Default Re: What if the Fuel pressure regulator failed...

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.
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Old 01-24-2008, 01:14 PM   #7
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Default Re: What if the Fuel pressure regulator failed...

Check fuel pressure first. GEMS engines can log codes for misfires and lean condition with low fuel pressure, but the LUCAS EMS is too crude for this.

Could well be either the fuel or coolant temp sensor.
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Old 01-24-2008, 01:59 PM   #8
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Default Re: What if the Fuel pressure regulator failed...

Will do that, thanks for the thoughts guys!

delash
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