Expert: autohelp - 12/4/2009

Question
I have a 1994 Cadillac Deville with a 4.6 engine. Had a problem with starving for fuel and replaced the fuel filter. Ran OK but after warming up for a while and after driving fine. started starving for fuel again. Tested fuel pump pressure and found pump bad(10 lbs). Replaced fuel pump, ran great for about 20 minutes then problem started all over again. Again replaced fuel pump since I no longer had borrowed gauge, ran great for about twenty minutes then same problem. Replaced fuel relay, ran great for about twenty minutes and same as before. I can go out right now and fire it up and it will run great for about twenty minutes. I can then turn it off and wait ten minutes and it will go through the same process again. When the problem is happening the car will run but if you give more than slight gas it will bog out. If you continue to give it light gas it will actually slowly accelerate. Very frustrating. I am a decent mech on old vehicles but do not get the newer ones. Also I cleaned the battery cables and under hood ground. Any ideas? Thanks in advance for your suggestions.

Answer
You need to install a fuel pressure gage on the fuel line and then we can perform some simple diagnostics to see if your problem is either with the:

oil pressure switch which acts a a dual switch .

When you first start the car the fuel pump relay is engaged for 2 seconds to prime the fuel system. Once the engine starts the fuel pump relay is BYPASSED and battery voltage is provided from the computer thru the oil pressure swict and then to the fuel pump.

Please e-mail: onlineautohelp@msn.com in order to obtain the information necessary to fix your vehicle.

If you are mechanicaly inclined or know of someone who is, You will need a DIGITAL VOLT/OHM METER, Simple electrical schematics, Test procedures and picture locations of the components within the system that is causing you problems of which can't be done on this website which only allows one picture. I do not have a website so you will have to e-mail: onlineautohelp@msn.com