Will there be any pressure at the gauge with a bad LP? I will have 14-14.5 psi at idle, and 10 psi at .75 throttle. everything running great. Then come to a stop and suddenley pressure hovers around 10 psi, and remains the same under acceleration. Then it will decide to return to normal when it desires. usually after 3 miles or so. (city driving). LP or Gauge or ?
Thanks Dieselho

 

Do you have a issolator? If so I'd be suspicious of the issolator, if not it's probably the pump. That's what the stock pumps do when the're getting ready to fail.

 

I had an isolator when i first purchased the FP gauge, and could not get an accurate reading so i by-passed it. I'm still curious though if there will be any pressure reading at the gauge if the LP is bad. I tapped into the fuel line just before the schraeder valve on the VP-44.

 

No there would be no pressure before the vp44 if the lift pump was completly out, but they usualy die slowly.

 

As I figured. Thanks for the input.

 

The LP impeller is plastic. If yours is failling like mine did, the hole in the impeller is getting worn out and no longer fits the drive motor shaft properly. This allows slippage and causes the pressure to vary. If this is your problem, it will fail very quickly.

 

It is? For what I could tell from close inspection, the LP is a vane type pump with steel rotor and blades, sort of like the power steering pump but small. Failure mode on mine, I am sure, was the bypass valve stuck open. Mine had zero pressure.

 

wrong, it's metal