Thread: EFI Fuel Rail Pressure

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After you do the injector " leak test "
Would it be redundant to do a FPR " test " ?

1) Disconnect feed line prior to FPR { to verify constant flow for a few seconds } Re connect.
2) Disconnect return down stream of FPR { verify consistent return } a few seconds. ( Long enough for pressure to drop? ) Re connect.


Wondering if # 1 would set a base to verify constant flow, then
if # 2 would have appropriate return volume?

Is it possible you got bad // contaminated gas at the station with sediment that found a way to the injectors & FPR?
Just a thought.

Well, I said it would be a learning experience. This morning I pulled all of the plugs and the ones on the right side were pitch black and very sooty. Number 5, 6 & 7 were better with dusty red electrode color, but sooty around the base and number 8 was black & sooty. I was really scratching my head, and decided to send an explanation of what was happening to my technical guy at Edelbrock, along with my fuel map and pictures of the plugs. He came back quickly with, "I wonder if your FPR has failed? Pull the vacuum line from the back side and see if you have any raw fuel in it." Well, that FPR vacuum connection is about as deeply buried as it can be, but I knew that it connected to the plenum so I pulled that end, sniffed of it and it was indecisive. Being old school, I bent down and sucked on the tube lightly, but still got about a teaspoon of raw gas in my mouth and dribbling into my beard - NASTY, NASTY, NASTY!! Turns out that FPR is a spring loaded diaphragm valve which balances manifold vacuum to regulate fuel pressure, and when the diaphragm ruptures it's sucking raw fuel into the plenum. Since the plenum connection is centered on the right side high, the right bank gets more "benefit" of the extra fuel than the left, but they all get extra.

The best part of the story is that when I went back and confirmed that the FPR was indeed the culprit he asked for my mailing address and said he would send me a new one to replace the failed unit under warranty. I responded that I had not expected that, and that I was simply hoping for some pointers to shortcut the process of solving the problem he said he knew that it wasn't that old, and that he appreciated that I had sent them so much feedback on maps and correction curves. Talk about great customer service!! I think Jeffery's been taking lessons from Vic!

T-top, you were right to point toward the FPR, and I was resisting because I didn't understand that it could suck raw fuel in a failure mode. I was struggling how a bad FPR could yield a rich condition.... Lesson learned, and a fantastic finish to a frustrating problem.

A vacume or boost referenced pressure regulator is one of the only ways that excess fuel can get into an efi engine where everything that normally causes an adjustment to the fuel is by sensors--primary is of course the O2 which can read an lean condition from an leaky exhaust part-others are malfuncing throttle position, manifold pressure,mass air flow, and inlet air and water temp sensors--


You certainly can't overlook basics even with the most elaborate electronic stuff available------ good going Roger and hats off to the guys at Edelbrock for as usual being so focused on customer issues-------------

I've had great experiences with Edlebrock! Quality stuff, great support!

As a bonus, I've noticed that the raw fuel aroma in the garage seems to be gone since the FPR was changed. I think that as I pulled into the garage at idle the leaky diaphragm was providing a straight shot of gasoline into the big plenum which then evaporated over time. Of course it's cooler now, too, but it's definitely better than it was. I need to put my wide band O2 sensor/indicator on it and go out cruising to check my map at high vacuum/cruise, when the leak could have been contributing to the fuel charge in unknown doses....