noticed i wasn't hearing the LP while waiting for the glows to heat today.
normally i can hear it inside the truck.
LP is pumping fine while engine is running, so OPS is ok.
LP comes on as soon as engine starts.
jumpered 12v to the fuel relay on firewall and the LP turned on ...also the fuse looked good.
tested for 12v at the LP with fuel relay jumpered and got 12v ok.
tested ground wire at LP w. fuel relay jumpered and it was ok too.
tested for 12v at the LP with just key on and no power.

ignition? broken wire? another fuse i don't know about?
any suggestions welcome. tia.

ok. i found some posts from gmctd and others that discussed conditions that turn on the lift pump.
96 and up obd2 is supposed to come during wait-to-start.
since i'm obd1, then i should not be getting LP power during key on, only during cranking.
if that's the case, then there's no way i should have been hearing the LP during the glow cycles.....now i'm really puzzled....cuz i've heard it.
i've also heard it run for a few seconds after shutdown, i assume cuz there is still compression lingering and the OPS is engaged.

could the OPS contacts be shorting and intermittently feeding key-on power to the LP before startup?

since the crank cycle is short , the truck seems to start at the same time i get power to the LP, i can't tell if the power source originates from the OPS or not. how can i test cranking cycle power to the LP without starting the truck? ie. an extended crank cycle... thx

I decided I no longer wanted to worry about the whole OPS headache with these trucks. I cut the power wire to the OPS that feeds the LP and replaced the fuel pump relay with a fused jumper that powers the LP with the key on.

Oil pressure gage works as normal, LP is continuously powered thru the fuel pump relay circuit from 'key on', instead of thru the OPS after oil pressure comes up.

Total cost was $7 for the fused jumper.

If you're not interested in that, it sounds to me like your system is working correctly now anyways, so I wouldn't do anything except check your fuel line pressure.

i'm still concerned about pumping fuel with key on in a wreck.
so how about this:
1. install Howie's OPS relay to ensure good quality 12v power to the LP during engine on.
2. install a push button switch ( only on when finger on ) w. a double relay to extend glow cycle(mod has been discussed on other posts ), and simultaneously power the LP

i get the LP on sooner, get extended glow cycle if needed, and still have the safety factor.

another option would be to run a relay off the 'glow' fuse...LP is on when glows are on. how hard would this be?

Do the OPS mods Howie posted about failing OPS will cause intermittent LP power, plus I'd put a 12V LED in power line to LP so when it's lit you know pump is getting power, for extended glows make sure your plugs can handle extended glow 60G or Kennedy quick heats are what you need to safely go with extended glow cycle.