Questions and Answers

DeVille Fuel Problem Q. Hi, I hope you can answer a quick question for me, I have an 1989 Cadillac DeVille. It has 141,000 miles, A/C, A/T, P/S and no anti-lock brakes that cuts out when climbing a hill or overpass. It's more noticeable at speeds over 70 mph. I've replaced the distributor cap, rotor, module, map sensor and coil.

The car was tuned up about 5,000 miles ago and ran great after it was done. One thing I have checked is the fuel pressure it seems low to me for a DFI system, I have a Chilton's manual and in one section it list 10.5 nominal psi and in another it lists 39 psi constant fuel pressure which is correct? The pressure also drops right to 0 psi when the car is turned off, is this a fuel pump or fuel pressure regulator problem or normal?

Thank you,
Tom

A. The correct fuel pressure for the 1982 to 1989 4.1 liter and 4.5 liter with the throttle body injection is 9 to 12 psi and should rise as engine speed increases. The pressure is a little on the low side so you may have a fuel pump going bad. If the pressure doesn't rise when the rpm is increased, then you have a bad fuel pressure regulator. The pressure dropping to zero when it's shut off indicates a bad fuel pump check valve. This valve is supposed to hold fuel pressure in the system when the pump is not running for easier starting.

The fuel pump check valve is part of the fuel pump, so to replace it you have to replace the whole pump. The fuel pressure regulator can be replaced as a separate unit.

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