Why do I have high fuel pressure...

steve meltzer · #1 (**permalink**) 02-26-2017, 10:12 PM

Probably won't get to this for a week or so, but will post the data. thanx so much. All of this makes sense to me. thanx again. s

patrickt · #2 (**permalink**) 02-27-2017, 11:24 AM

Quote:

Originally Posted by steve meltzer

Probably won't get to this for a week or so, but will post the data. thanx so much. All of this makes sense to me. thanx again. s

OK, so we have:

I've owned the car for nearly 15 years and it's always run about 6 PSI at idle with either the mechanical or the mechanical + electric.

Perfectly normal; as it should be.

On the road, same until about 3K RPM when, under load, the mechanical pump falters, dropping the pressure to 2-3 making the car stumble. Switching on the electric pump solves that problem and the pressure returns quickly to 6 and remains there, as long as the electric pump is on. Been that way forever, but now....

Hmmmmm, maybe the mechanical pump is collapsing the rubber fuel line coming in to it, thus causing the output pressure to drop to 2 to 3. Then when you switch the electric pump on it opens the collapsed rubber line back up and the pressure is restored. That would do it... and it would be a damn tricky gremlin to find.

... and now

The car idles and cruises at 9 PSI, e-pump off. But still stumbled until I flipped on the e-pump and then it ran great.

Either the gauge is wrong or the mechanical pump is now broken. If you have a little Go-Pro camera, it would be interesting to see if the rubber supply line, either right by the fuel pump or maybe back at the tank itself, is collapsing on load when the electric pump is off. But, regardless, we'll figure it out. There's not that many things it could be.

steve meltzer · #3 (**permalink**) 02-27-2017, 05:31 PM

Yep Patrick, you got it perfectly. I'll get to check the pressure ASAP, but I don't have the GoPro, tho' i do know what it is! If it's the mechanical pump, maybe I just put a plate over it and run the line to the fuel rail. Do they make sucha plate so I can just ditch the mechanical pump....tho' it's nice insurance should the e-pump fail. thanx again. more later. s

patrickt · #4 (**permalink**) 02-27-2017, 05:41 PM

Sure - it's just a block off plate. Like this: https://www.summitracing.com/parts/p...view/make/ford but the next time you stroll through the garage, bend over and see if you pinch the black fuel hose going to the mechanical pump close with your fingers. If it feels "squishy," then it may be collapsing on you.

Morris · #5 (**permalink**) 02-27-2017, 07:28 PM

Quote:

, maybe the mechanical pump is collapsing the rubber fuel line coming in to it, thus causing the output pressure to drop to 2 to 3. Then when you switch the electric pump on it opens the collapsed rubber line back up and the pressure is restored. That would do it... and it would be a damn tricky gremlin to find.

And maybe the filter inside the electric fuel pump is partially dirty and restricting the flow of fuel to the mech pump....then when the electric pump is activated, it forces enough fuel to the mech pump to provide enough fuel for the engine.....

I'm just saying ...gremlins do exist with a 15 year old pump...

patrickt · #6 (**permalink**) 02-27-2017, 07:38 PM

Quote:

Originally Posted by Morris

And maybe the filter inside the electric fuel pump is partially dirty and restricting the flow of fuel to the mech pump....then when the electric pump is activated, it forces enough fuel to the mech pump to provide enough fuel for the engine.....

I'm just saying ...gremlins do exist with a 15 year old pump...

Maybe. But Steve says it's "Been that way forever..." -- and I can see the installer reaching for a worn out piece of hose when he dropped the engine in.

It held up long enough for him to get it out of his shop. But, it's sure easy to just bypass the electric pump fuel lines for quick test up to 3K. Of course, he still has that pesky 9psi coming out of the mechanical pump. Unless his gauge is wrong.

steve meltzer · #7 (**permalink**) 02-27-2017, 08:06 PM

OK, the pump is only about 5 years old (the original Holley died), maybe 3-4, and the failure of the mechanical pump (which only occurs under load...can't replicate it revving it up in the garage) antedates that.
I installed the engine and all, with the help of my friend who's an excellent mechanic, so I don't think it was junk hose to start. Thinkin' about bypassin' the mechanical pump, but let me get out there (not sure when!) and at least see if it's the gauge. thanx for all of the good help. steve