The fuel pressure regulator blues

My 91 245 NA blows through fuel pressure regulators like nobody?s business. I?m lucky to get one year out of them. I bought mine from pep boys because they have a lifetime warranty but it?s getting to be a pain because the only pep boys that stocks it is about 15 miles away. The car starts great when the engine is cold but when I restart it after it?s been run for a few minutes it?ll want to stall for about 10 seconds if I don?t have the throttle slightly open. After about 10 seconds the idle stabilizes and everything is fine until I turn the car off again. Switching out the FPR cures this problem for about 9-12 months and then the cycle begins again once I replace the FPR. I?ve tried OEM Bosch And aftermarket FPRs and the lifespan is always 9-12 months. The vacuum hose for the FPR does smell like fuel but I?ve never seen it flow from there. The CEL will flicker if the idle dips low enough when restarting but there aren?t any stored codes. I replaced the ecu temp sensor a few years ago and the resistance is in spec. I did all of the tests described in the LH2.4 green book and found nothing wrong. I suspected the main pump might?ve been switched out to an incorrect one but I can?t find any legible markings on it anymore so I can?t determine if it?s the right one. I?m planning on shooting some compressed air through the return line tomorrow to see if it?s clogged up. After that, I?m all out of ideas and I?m sure pep boys will cut me off on their regulators at some point. Any suggestions?

Matt

Clogged return lines are uncommon but it's a possibility so definitely check it out. I have seen some melted lines when they come in contact with the exhaust.

Put a fuel pressure gauge on it.

If that's a K-jet pump it puts out 5 bar vs. the 3 bar the system requires. Trying to relieve all that excess pressure could lead to premature regulator failure.

hiperfauto said:

Clogged return lines are uncommon but it's a possibility so definitely check it out. I have seen some melted lines when they come in contact with the exhaust.

Put a fuel pressure gauge on it.

If that's a K-jet pump it puts out 5 bar vs. the 3 bar the system requires. Trying to relieve all that excess pressure could lead to premature regulator failure.

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Thank you! I think I?ll try looking harder at the pump tomorrow. I noticed that the kjet pumps are powered by ring terminals which I don?t remember seeing on mine but I could be wrong. Maybe there was a cosmetically identical pump that outputs 5 bar instead of 3. Bmw, Mercedes or something?

No, ring terminals are used on aftermarket pumps. The original pumps use pin contact terminals with a locking plastic cover so they can't rattle off.

Ring terminals with lock washers should not rattle off

Ok so I put a fuel pressure gauge on it. With the car running I was getting 36 psi with the vacuum line to the fuel pressure regulator plugged in. With the vacuum line pulled I was getting 43 psi. Squeezing the return line while running caused the pressure to spike rapidly indicating a bad regulator. After shutting down the engine the residual fuel pressure dropped like a rock and went to zero within a few minutes . I replaced the fuel pressure regulator, blew through the return line with compressed air and now get 34 psi with the vacuum line attached and 43 with the vacuum line blocked off. Residual pressure after 20 minutes is about 30 psi now. I don’t think there was any blockage in the return line so I’m pretty sure I’m back to square one on this one and the cycle begins again. The main pump is an OEM Bosch 3 bar pump part number 0-580-464-039 so that doesn’t appear to be a factor. Maybe these fuel pressure regulators are just normal maintenance items for me at this point. Super aggravating.

mattd1205 said:

With the car running I was getting 36 psi with the vacuum line to the fuel pressure regulator plugged in.

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Okay.

With the vacuum line pulled I was getting 43 psi.

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Okay again.

Squeezing the return line while running caused the pressure to spike rapidly indicating a bad regulator.

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Uh, no.
That result is 100% normal, and expected.

The pump *can* put out probably 90 psi, if it needs to. The regulator bleeds off all that pressure to the level the engine needs to run properly, and is set by the FPR's spring-loaded internal valve, and modified by the vacuum signal.

All you did was prove that your pump is healthy.