Lift pump pressure spikes after shutdown

[Steve Graham]

This adventure started out with the engine not starting after setting for a few days. It would start after priming with the lift pump but without bleeding. I temporally installed a 0-15 psi analog gauge at the banjo bolt to the filter to check the pressure.

It has good pressure at cold idle (8 psi) and a small bit of throttle it would climb to 12 psi and just after shut down the psi will wrap the needle all the way around and then slowly drop to zero psi. (climb past 15 psi >18psi?),This can't be normal!


My guess is the IP (VE) if feeding the pressure back to the top of the lift pump. But why, how?

Ideas, suggestions?

The lift was replaced July of 2017.

 

[cerberusiam]

IIRC, there is an internal check valve to bleed excess case pressure back to the supply side. It will stick and not work correctly, that would push case pressure back into the vane pump and back to the LP. Short answer is should not do that.

 

[Steve Graham]

Found 2 culprits. The first gauge was reading high/defective, replaced it with a new one and readings were in spec.
The spike only appeared on a cold engine, tested this on the engine at normal operation temp and the spike did not happen. False alarm.