Cadillac Repair: 1991 DeVille 4.8 stumble/stagger, fuel pressure gage, rotor coil

Question
This is a copy of a question posed previously in 2006:

Expert: autohelp
Date: 5/2/2006
Subject: 1992 Cad Deville engine problem

Question
I have an intermitent problem with the engine sputtering and loosing power. Sometimes it runs great and other times hardly runs at all. I have taken it to 5 mechanics and spent over 2000 with no solution. Have replaced all electrical ignition componets except pick up coil. One mechanic said it was fuel pump but that he did not do fuel pumps and sent it out to another mechanic who tested it and said it was not the fuel pump, replaced the hall sensor and worked on the grounding wires. No improvement. Afraid to put any more into it just trying stuff. No error codes. I has good compression. Put on new fuel filter, plugs, wires, cap, rotor, coil, ignition module, hall sensor, 2 mufflers, and cat converter. Backfires a lot when missing, blew apart 2 mufflers.
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However, I am not backfiring.  I have not had many hands in this car.  But it will die after awhile and sputter under any extra load (passing etc).  Gets worse when it the car gets warm.  Fuel pump has 50 psi.  New wires plugs and cap.  Any help you can give me here?  With only 80,000 miles, it is almost unusable as is.  ECM?  Temp sensor? O2 sensor? I'm just drawing for straws.  Like its too lean, no smoke, hot exhaust.

Thanks for your help.


Answer
Put a fuel pressure gage on it and tape it to the outside of the windshield where you can monitor the fuel pressure as you drive it for a few days. have caught many a fuel pump causing intermittent low pressure at times.

Your fuel pressure should be between 40 and 50 psi.

You could have a fauklty pressure regulator, A faulty pulsator on the fuel line in the fuel tank, A faulty check valve in the fuel pump, an intermittent faulty pump or faulty leaking/partially restricted fuel injectors.

I can direct you to someone who can provide pictures and excellent test directives to isolate your problem and the tests are very simple to do.

E-mail: cadillactech@hush.ai