Engine Performance problem
1990 Cadillac Deville V8 Front Wheel Drive Automatic 108000 miles
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Hi Team,
I just bought a 1990 Cadillac Deville, It has sit for about 7 months and the car requires premium fuel but the past owners were putting mid grade fuel in the car for several years.
I’m starting to get a rough idle and backfire when I press on the gas, also when I sit at a light and I also get a stall and loss of power when I press the gas pedal while driving. Sometimes it clears up and the car runs great. Do you think this is because of the gas, fuel pump, or something else?

Lets get the fuel pressure check with a fuel pressure gauge designed for your fuel system-to rule out the fuel filter, pressure regulator and fuel pump-could be bad fuel- I need the fuel pressure readings for evaluation and direction to take-

Or you can do below immediately when is stalls out to determine if its fuel or spark problem

Get a carb cleaner and spray into the carb or the throttle body on an EFI. Did it start and die? If not disconnect a sparkplug wire or 2 and ground it to the engine -have helper crank engine over-do you have a snapping blue spark? If so-you have a fuel problem, check the fuel pressure to rule out the fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light.

Fuel pump/Pressure Regulator and Injector/s checks out-start checking the ignition system-power to coil, coil/s itself,distributor pick-up,control module, Cam and Crankshaft sensors.

If both fuel and spark is present-check the valve and ignition timing, this will lead you to problems with compression and valves opening and closing at the wrong time

TYVM for using 2carpros and I'll be waiting for your return as needed-

rasmataz wrote:

Lets get the fuel pressure check with a fuel pressure gauge designed for your fuel system-to rule out the fuel filter, pressure regulator and fuel pump-could be bad fuel- I need the fuel pressure readings for evaluation and direction to take- Or you can do below immediately when is stalls out to determine if its fuel or spark problem Get a carb cleaner and spray into the carb or the throttle body on an EFI. Did it start and die? If not disconnect a sparkplug wire or 2 and ground it to the engine -have helper crank engine over-do you have a snapping blue spark? If so-you have a fuel problem, check the fuel pressure to rule out the fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light. Fuel pump/Pressure Regulator and Injector/s checks out-start checking the ignition system-power to coil, coil/s itself,distributor pick-up,control module, Cam and Crankshaft sensors. If both fuel and spark is present-check the valve and ignition timing, this will lead you to problems with compression and valves opening and closing at the wrong time TYVM for using 2carpros and I'll be waiting for your return as needed-

Razzy codes need to be checked first, off and warmer on the heater controls with the key in the on position. look in the fuel message center for the codes, starts out 8.8.8 and ends with 0.7.0

I believe for the backfire the AIR pump and Diverter valve are bad