About a year ago I replaced my fuel regulator on my NA 87’ 944. It seemed to help with the intermittent hesitation while under load but not completely. I have since installed a hose on the end of the fuel rail, ran it inside the car, and attached a pressure gauge to the end. It sits in the compartment just under the stereo. It works really well and easy to cover up when needed.
At any rate, when the car is under a load, accelerating, the gauge will fluctuate very rapidly between 30 and 40 psi. Is that normal? I have done the pressure regulator check (pull off vacuum line, crimp hose, etc.) shortly after installing the new regulator and it was fine. I must admit I have checked it lately. I probably figure that it wouldn’t go bad that soon and because it never completely solved the problem, I didn’t see a reason to check it again. Should I? I have also performed the fuel pump output test several times with passing results. However, I wonder how good the test is because it not performed under pressure.
Any comments and opinions would be greatly appreciated.

Thanks in advance.

John Mobley

 

One of two things: Either vacuum or the damper.

The damper is supposed to smooth out fuel pressure changes caused by the injectors opening and closing, and the damper is controlled by manifold vacuum. Put a vacuum gage on the line to the FPR and damper and then watch vacuum while the engine is under load/accelerating.

If vacuum is bouncing then chances are you have an issue with a valve or valve spring.