6.5TD lift pump wiring - Diesel Bombers

Chevy/GMC 6.2L and 6.5L Discussion of Chevy and GMC Trucks with 6.2L and 6.5L Diesel Engines

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Old 03-26-2013, 08:44 AM
Diesel Fan
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Join Date: Mar 2013
Posts: 22
Default 6.5TD lift pump wiring

Morning guys, several of you think that I have a problem with the Oil Pressure Switch that is causing the problem that I have with my engine when I first start it and drop it into gear.
I have a question. I absolute HATE "Automatic" stuff, because it usually STOPS "being automatic" at the worst times, my lift pump for example. I am a pilot, and am used to having fifteen switches for systems that are NOT automatic, and I have never forgotten to throw a switch yet.
Why not just run a wire from the positive side of the battery, or the "Run" terminal on the ignition switch in the truck? Run it from there to a switch of the plastic steering column cover, and from there to a fuse, and then on to the lift pump. THEN the OPS can just be for the Oil Pressure Gauge, and I have an EASY way to bleed the fuel rails without having the engine on?
(You guys ought to see all the switches on the panels of my Jeeps, and the F-350, they look like the panels of a Winston Cup car).
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Old 03-26-2013, 12:10 PM
racer55's Avatar
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Join Date: Oct 2012
Location: Scugog Island ONT.
Posts: 1,841

The OPS is a safety factor in the event of a crash-when the engine stalls fuel stops pouring out ontpo the highway waiting to catch fire.

If you resort to a switch and become incapacitated,the safety factor is gone and you run the risk of being BBQ'd.

Besides on a 98 the OPS is only a secondary power source for the LP.

The primary power for the LP comes from the LP relay that the ECM activates when it senses the engine is running from CPS or OS inputs.

If your LP runs during the glow cycle to prime the fuel system the relay is working properly.

The LP running after shutdown for a few seconds is a product of the OPS sending power while the oil pressure bleeds off.

This applies to all 96+_ C/K trucks.

The OPS is the primary power for the LP on 95 or earlier trucks only.

As for bleeding after a filter change-apply 12v to the red wire with the insulator that exits near the underhood fusebox below the master cylinder-that will activate the LP through the relay also.
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