I'm going to replace my fuel pressure regulator this afternoon- the part will be in later, and I wanted to remove and test the old unit first.

The car is an '86 745 turbo. The O2 sensor reading seems to indicate a rich mixture (voltage .8 to .9 volts). When I create a vacuum leak, I see the O2 sensor voltage lower. Removing vacuum at the fpr does not result in a higher idle- I believe I read somewhere that it should. Fuel mileage is poor, and this came along with a reduction in performance recently.

I assume that after removing the two bolts securing the fpr to the intake, the fpr will simply release from the fuel rail.

I read in the FAQ that one way to reduce fuel pressure at the rail is to apply vacuum to the fpr so it will dump the fuel into the tank. I don't think this will work in my case as the FPR may have failed closed. I also read you can simply run the pumps with the motor off, but don't understand why the pressure still wouldn't stay high with the pump working against the closed FPR.

[Edit- just re-read FAQ on relieving fuel pressure. Pulling the fuse on the pump and running the motor dry makes much more sense. Thanks to all for that great resource.]

Any advice regarding this diagnosis or replacement is appreciated.

-Dylan