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Discussion Starter #1
Ive read through the FAQ list but its still unclear to me if the OPS is the reason for the lift pump to be inop, will the op gauge on the cluster still work?

I don't hear the LP when the key is turned on nor does it run when the truck is. I can "hotwire it" at the relay by jumping the orange/grey terminals and I've confirmed it does run then. Am I a candidate for a new OPS?
 

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Sounds like it.

ACDelco OPS only D1808A, IT IS HARDLY AVAILABLE LOCALLY.

There are 2 circuit on the OPS, one control the LP and one send signal to the gauge.
The one that control OPS can be bad without the other being bad.
They are sort of independent of each other.
 

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Discussion Starter #3
Ahh. Figured if it wouldn't run the lift pump it shouldnt register on the cluster either.

You guys generally buy the OPS online then with local sourcing being scarce?
 

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RockAuto or stealership.
 

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Discussion Starter #6
Thanks. Ill look into the dealer tomorrow and see what they have.

Working on the relay mod right now.
 

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Discussion Starter #8
I understand that. I had time today to tackle it so its ready when i get the new OPS in.
 

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Discussion Starter #9
Got a new OPS in and did the relay mod. Started it up and it worked however the pump didn't run when the key was on, only when the truck was running and had built oil pressure. Took it for about an hour drive and when I got home the pump wasn't running again. WTF. Looks like I'm wiring the pump to a keyed source and screw this OPS setup.
 

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LP on a 93-95 never runs when cranking. It ran solely on oil pressure.

That is the feature from the factory, called GM.

If you want, you can make the relay to run the LP during WTS by connecting the "normally closed" pin to a "ign ON" fuse.

If the LP is not running when engine is running and you have done the mod, check the mod, make sure it is connected properly.
If they are connected properly, then the LP is bad.
 

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Discussion Starter #11
If the LP is not running when engine is running and you have done the mod, check the mod, make sure it is connected properly.
If they are connected properly, then the LP is bad.
The pump worked before I went for a short drive. When I got home it had stopped. Fuses are good (5 and 20 amp) Lift pump is brand new and verified it works by connecting to a direct 12volt source.
 

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My 94 and 95 have a relay, that activates the lift pump when the key is turned to start. One pre 95 trucks look on the passanger side firewall. Under the plastic shield there is a lift pump relay there. On 95 and up its in fuse box.
 
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The pump worked before I went for a short drive. When I got home it had stopped. Fuses are good (5 and 20 amp) Lift pump is brand new and verified it works by connecting to a direct 12volt source.
Put the 12V direct again to see if the LP is still good.

Brand new does not mean it works, yet.
It can fail even after a short drive.
A lot of them are made in overseas or neighbor to the south.
Nothing against them, it is just not the greatest quality control.
 

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For future reference for other people, O'Reilly stores can get you the ACDelco D1808A for $38, not sure what the dealers charge.
 

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Discussion Starter #15
Put the 12V direct again to see if the LP is still good.

Brand new does not mean it works, yet.
It can fail even after a short drive.
A lot of them are made in overseas or neighbor to the south.
Nothing against them, it is just not the greatest quality control.

Yeah I did throw the 12volt to it after I noticed it wasn't working when I got home after taking it for a drive. The fuses were both good as well. The only thing I didn't check now that I think of it was the relay. Ill swap in the spare I have after the kids are in bed.
 

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Discussion Starter #16
For future reference for other people, O'Reilly stores can get you the ACDelco D1808A for $38, not sure what the dealers charge.
I couldn't find a local vendor that carried ACDelco other than the Dealer. I got a good look at my ankles when I coughed up $75 for it.
 

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I wired my lift pump straight to a switch on my dash. It's not the most civilized method, wire from battery to switch to lift pump with a fuse in there somewhere for safety , but it's been working well for about 5 years now. I used some fairly thick wire so it doesn't over heat the wire. It's nice to be able to prime the fuel filter without starting the engine too. Or pump fuel into a container through the water separator drain. Only disadvantage I have noticed is if forget to switch it off it will kill the batteries in as little as an hour or two. And most vehicles out there don't have the power output to jump these trucks.
 

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Discussion Starter #18
I swapped in a new relay and everything is working again. I can't say Ive ever had a relay fail in such a short time before. Ill get a few more hours of seat time in it tomorrow and make sure Im good to go. Thanks for the help guys
 

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1993-1995 the lift pump runs during cranking via the lift pump relay. The relay is disabled when the key goes to ON position.
It never turns on in my truck during cranking not until I added the relay mod.

The 96+ that turns on during cranking to prime.
 
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