Lift pump no power

[Unboy2000]

Good day, I have been working on this problem all day...There is no power going to the lift pump. Any input would be appreciated.

I verified the fuses; even fuses that had nothing to do with that pump.
I verified the relay; the relay work if I inject 12V but no power to that relay when the inginition key is on.

So where that relay is getting the 12 volts from?

The truck run well even with that pump unplug...The only problem I noticed is if I park the truck uphill engine up the truck will be hard to start, downhill start like new

Thanks

My truck in 6.2 1992 4X4

[Roachie]

Have you tried just wiring up a cable from battery ( + and - ) directly to the pump? This will tell you if the pump itself is broken. If it works okay with the power applied directly, then at least you know it's not the pump itself that is faulty.

If there is no power getting to the relay, you need to work backwards from there to the battery to see where the power supply stops getting through.

[JohnC]

The relay only powers the pump when cranking. When the engine is running it is powered by an oil pressure switch co-located with the oil pressure sensor for the dash, on the back of the block at the base of the driver's side head.

Note, if you are not cranking and there is no oil pressure (engine not running...), there will be no power to the pump.

[Unboy2000]

Very useful info guys; you put me in the right direction; I also found a circuit diagram that show what JohnC says; the Run mode and Cranking mode...

Roachie; the pump make some noise when I apply 12 volt directly to it. But it does not sound healty...It make some sort of hisssssss... of course when engine is running can not ear a thing ;-)

Ok now let find that oil pressure sender/switch

[Unboy2000]

After getting all that information; I was able to confirm that my pump is really getting 12 volts from both circuits...

Case close! thanks again