Archived Intermittent lift pump at start

[JLandry]

The ECM doesn't send a full 12 volts to the lift pump when you first turn the key and crank the engine.

Actually, the ECM provides full power to the lift for about 2 seconds when you first turn the ignition key to the run position, and then it supplies reduced voltage while the ignition key is held in the start position (during engine cranking).



The ECM also provides full power to the lift pump for about 25 seconds when the starter is bumped but the engine is not started.



These are subtle but important differences when trying to trouble shoot the lift pump.



Best regards,



John L.

 

[PRout]

I use the power window circuit to trigger the lift pump relay (used a fuse tap that adds an extra fused circuit output to that fuse). Works perfect.

Pump runs whenever the key is on, but it momentarily stops while cranking the starter, so the VP isn't being jammed with pressure.

Also added a manual pump run switch on the side of the fuse box that bypasses the pump relay in case it fails, or the fuse ever blows. Neither has happened but its nice to have the manual pump switch under the hood for purging air from the system.

"Might" be a viable workaround for the ecm problem.

 

[KLockliear]

Yep, something like that was going to be my last resort.