I went out to do some VE learns with the EBL flash 2 today. I checked the fuel pressure after I was done the first session. To my surprise it was rapidly jumping around. It was not doing this the other day.

I have Ford Racing 30lb injectors and a LT1 adjustable fuel pressure regulator on LT1 fuel rails modified to fit the Edelbrock Pro Flo XT and stock 1987 TPI fuel pump.

I had the pressure set for 40 psi (Ford rated pressure) and it was holding nicely. Today it was rapidly fluctuating between 30-40psi with the vacuum line disconnected. With the line connected it was worse at 22-32 psi at idle. It almost seems its fluctuating with the opening of the injectors.

When I turn the car off the pressure gauge shows holding just shy of 40 psi.

I had just installed the AFPR the other day. Could this be the trouble? But it holds pressure fine with the engine off. The other day it was holding pressure while running just fine. Could it be the fuel pump? I have a new Walbro 255lph to install someday.

This is with the vacuum line connected:

This is with the vacuum line disconnected:

This is driving holding RPMs steady:

 

In my ignorant opinion, you should use a fuel pressure gauge because they're dampened to control the swing better. Also looks like you need to turn it up a little so it's averaging where you want it to be.

 

Agreed about the dampening. It appears the gauge is reacting to every injector pulse, and not handling it very well.

 

I have a autometer fuel pressure gauge on another car I'll take off and use to test the pressure on this car.

Does anyone know what the output of the stock tpi fuel pump is? I'm probably wasting time trying to tune before I install the 255lph pump.

 

You mentioned an adjustable regulator, does it have a vacuum port (it should, even if it is not hooked up)? My Aeromotive regulator vacuum port was threaded in too far and was binding the spring and would bounce around and not adjust smoothly. You should check for this and if you are attaching a vacuum line to the regulator, make sure the regulator is sealed or it will be a massive leak. Good luck.

 

Checked fuel pressure with a different gauge. Holding steady now.