careldo Posted January 28, 2004 Report Share Posted January 28, 2004 Hey guys. can anyone tell me what the normal fuel pressure reading should be with the car running in idle and what it should be with key on and engine stopped on the 4.9L. I'm getting 38 PSI key on engine off and 25 PSI engine idling. thanks, careldo Link to comment Share on other sites More sharing options...
PAUL T Posted January 28, 2004 Report Share Posted January 28, 2004 According to my manual for a 92 Deville with a 4.9 the pressure should be 45 - 50 psi with engine off. It says for a pressure over 50 psi the fuel pressure regulator is not working properly and pressure below 45 psi indicates a restriction in the fuel return line. Have you changed the fuel filter? My 92 Deville is doing the samething jumping from 20 mpg to 14 mpg. It won't start at all now and I am suspecting the fuel pump. A leaky injector will cause a drop in mileage also. It is indicated by a rich exhaust (rotten egg smell) and low pressure. There is a test to tell what injector or injectors are faulty but I am not sure what it is. Good Luck! Link to comment Share on other sites More sharing options...
KHE Posted January 28, 2004 Report Share Posted January 28, 2004 If you block off the return fuel hose and the pressure rises to the range that Paul listed, I would suspect the fuel pressure regulator. If the pressure remains at 25 psi, then I would look at the fuel pump. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
careldo Posted January 28, 2004 Author Report Share Posted January 28, 2004 looks like more work ahead hope its not the fuel pump thks careldo Link to comment Share on other sites More sharing options...
KHE Posted January 28, 2004 Report Share Posted January 28, 2004 looks like more work ahead hope its not the fuel pumpthks careldo The key is to properly diagnose the problem so you don't replace good parts. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
careldo Posted January 28, 2004 Author Report Share Posted January 28, 2004 i hear you careldo Link to comment Share on other sites More sharing options...
careldo Posted January 28, 2004 Author Report Share Posted January 28, 2004 is it possible for a FPR to leak back to tank to much fuel yet not leak externally? careldo Link to comment Share on other sites More sharing options...
KHE Posted January 28, 2004 Report Share Posted January 28, 2004 is it possible for a FPR to leak back to tank to much fuel yet not leak externally?careldo I believe it's possible for that scenario to occurr. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
careldo Posted January 28, 2004 Author Report Share Posted January 28, 2004 so let me get this straight if to much fuel is going back then that will account for low pressure readings thus blocking the return line should bring the pressure up excluding the fuel pump as a potential problem. i am going to try this tonight. careldo Link to comment Share on other sites More sharing options...
Ranger Posted January 29, 2004 Report Share Posted January 29, 2004 looks like more work ahead hope its not the fuel pumpthks careldo Put the fuel pressure guage back on and take the car for a ride with the guage taped to the windshield (if it's long enough). The pressure should remain relatively constant. If it drops drasticaly when you accelerate then the fuel pump is headed south. If the hose is too short you should be able to perform the samne test by revving the engine. Link to comment Share on other sites More sharing options...
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