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Politically Incorrect
Join Date: Aug 2005
Location: Hoover, Alabama
Posts: 1,494
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Bad FPD?
I'm still trying to find the cause of the slight hunting at idle. I just measured my fuel pressure and I need an opinion.
BEFORE I replaced the Fuel Filter: -32 PSI steady, cold engine -40 PSI steady, cold engine, vacuum line disconnected and plugged AFTER I replaced the Fuel Filter: -31-33 PSI blurred needle, cold engine -40 PSI steady, cold engine, vacuum line disconnected and plugged FPD is original based on PO's records. No fuel leak or odor from the FPD vacuum line nipple. Does a blurred needle mean the FPD is bad. I'm thinking it does, but I'm not positive. Could this be the cause of my slight hunting at idle as well? I don't think the fuel pump inlet screen (in the tank) has ever been touched either.
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Edek '87 924S '91 535i |
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05-16-2007, 02:58 PM
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When dampers go bad they leak gas out of the vacuum hose fitting. When fuel pressure regulators go bad they might leak fuel but usually over pressure the rail causing a rich running condition to complete shut down of the injectors. Fuel pressure can keep them closed.
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Hugh - So Cal 83 944 Driver Person NOT a 'real' Porsche -- Its Better!!!! When was the last time you changed your timing and balance belts and/or cam chain and tensioner? New Users please add your car's year and model to your signature line! Never break more than you fix! |
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05-16-2007, 06:07 PM
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Politically Incorrect
Join Date: Aug 2005
Location: Hoover, Alabama
Posts: 1,494
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Yes, I have first hand experience with a bad FPR. Overpressure was the problem. However I do not have any experience with failing FPD's. Isn't it the job of the FPD to damp out pulsations caused by the injectors opening and closing? If so, shouldn't fuel pressure readings at idle be rock steady? I've checked for vacuum leaks with an unlit propane torch. I've checked for bad wires with a water misting in the dark. Rotor is not loose. O2 sensor in or out makes no difference. Most of the other DME instrumentation is fairly new (temp sensor, plugs, coil etc.)
What I plan on checking next is: - bypass the MSD (it's over 30 years old!) - pull the fuel rail and observe spray patterns (my friendly local Porsche mechanic is betting on a bad spray pattern) - pull and bench test the AFM - the fuel return line for blockage - the pump inlet screen for blockage - last resort before replacing FPD will be to tear into the Motronicsvoodoobox to look for questionable components and solder joints I always do the free/cheap things first before throwing money at a problem. I like to know exactly what part failed.
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Edek '87 924S '91 535i Last edited by onZedge; 05-16-2007 at 09:04 PM.. |
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05-16-2007, 09:01 PM
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1983 Porsche 944 2.5 liter
