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Old 11-26-2009, 03:34 PM   #1
fords4me
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'90 mustang will bad fuel pressure regulator cause idle surge?

does anyone know if a bad fuel pressure regulator will cause my idle to surge and eventually stall. Ive cleaned IAC and there was no change. When I pulled the vacuum hose off regulator there is raw fuel in line. Im hoping when I replace the regulator it will solve my idle issues. anyone know for sure?
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Old 11-27-2009, 02:18 PM   #2
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Lightbulb Re: '90 mustang will bad fuel pressure regulator cause idle surge?

Turns out it was indeed the regulator. No more surge. My '90 mustang's idle was surging. It would rev then drop, rev and drop. Sometimes it would stall, other times it would even out and stay steady, depending on how long I stayed still. I noticed too while I was driving, it would feel like it was missing almost. Anyway I replaced the fuel pressure regulator today and my problem is solved.
I believe the vacuum was sucking raw fuel into the intake and flooding the engine or at least upsetting the air/fuel mixture. I got this below off a website about a test of and symptoms of a bad regulator. Hope it helps somebody.

Fuel Pressure Regulator Test
This test checks the operation of the fuel pressure regulator to make sure it changes line pressure in response to changes in engine vacuum. This is necessary to maintain the proper operating pressure behind the injectors and to compensate for changes in engine load.
With the engine running, disconnect the vacuum hose from the pressure regulator. As a rule, fuel system pressure should increase 8 to 12 psi with the line disconnected. No change would indicate a faulty pressure regulator, or a leaky or plugged vacuum line.
If the diaphragm inside the regulator is leaking, engine vacuum will suck raw fuel into the intake manifold through the vacuum hose (look for fuel inside the hose).
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