Lift pump test

[G B Sisson]

Hi, I did a search for lift pump test and found a method to test the 95 and earlier,but maybe Im missing something.The method was put truck in another gear besides park or neutral then turn key to start.It wont crank,but you will hear lift pump working in the start mode. This sounded great,even would pressurize system for those cold starts...only thing is,my key wont turn when it's not in N or P.What am I missing? thanks,GB

[moondoggie]

Good Day!

That's probably my old post. Works on both my 95's, but I know that a lot changed from 94 to 95 on the IP - it looks like that may be one of the things that changed.

Others here on the Page have hooked up jumper wires, etc, so hopefully someone will chime in here about that.

If you haven't already bought one, you might want to get a factory shop manual for your truck, available from Helm (http://www.helminc.com) (Click in colored text.). It will include adequate wiring diagrams to help with this.

Blessings!

Brian Johnson, #5044

[ucdavis]

Next to the Fuel Relay should be a red wire that had a white tag on it originally that said Fuel Pump Bypass or something like that, and that ends in a female spade connector w/plastic insulator around the spade receiver. Put 12V to that and you've got the easiest LP test going. Works w/engine off for priming an new IP...
Seems GM realized that lack of PCM monitoring necessitated at least some form of back up check for the mechanic. Later years monitor the LP, and may not have this wire tap.