I have a feeling my lift pump has gone south or the common OPS. The truck will crank and produce 45psi of oil pressure but no start, also can't hear LP. It has had the problem of stalling and surging for a week until now it will not start. It is definetely a fuel issue. If the sensor reads oil pressure can it still cut power to the lift pump? Thanks for any ideas.

Measure the voltage down there on the cable to the LP with ignition on. If there is none, then the OPS is bad. Otherwise, check the LP test in the FAQ.

Thank You just what I thought

Best way to test is to replace it. Has very poor contacts inside and sometimes it will work fine and sometimes not. Has no effect on oil pressure readings.

http://dieselplace.com/forum/showthread.php?t=39350

http://dieselplace.com/forum/showthread.php?t=39350 GM :ro):ro):ro)Good use of FAQ reference material :thumb::thumb::thumb:

GM :ro):ro):ro)Good use of FAQ reference material :thumb::thumb::thumb:

I used that page before when i was having problems, plus I learn from the best to give someone great information laid out in a good format for easy understanding.

Plus I'm bored....

I did a quick N dirty test, by pulling the connector of the OPS, and jumping across the two sockets with a paperclip.

Enter cab, turn key on, and listen for the pump.

Works OK, as you don't have to listen for it over engine noise.

While it rattles (IF it rattles), walk up front and check for flow at the bleed valve. Got flow, good, no flow, not so much good.

Then I tried it with the engine going. This way I was fairly certain that the OPS was at fault, ruling out wiring to the lift pump.

I ended up making a socket to pull the OPS, using the new one to find the size, but they are not too expensive, if you can find one. Mine serves as an injector socket on my VW too, so it was time well spent. :-)

Cheers
Trev

I ended up making a socket to pull the OPS

I just bought a crowsfoot for mine, made it a snap!

But I haven't tried that way before, nice.

It seems the OPS should only have two wires yet my truck has three am I stupid whats going on please help!!! part number or any advise on OPS. 93 3500hd mechanical injection pump. :(

Nope it is supposed to have 3, as the OPS sends sig to dash and lift pump, did you read the reference material, tests are explained there

With the engine running open fuel (water drain) drain valve on the t-stat housing if fuel runs out then ops/lift pump is working, if engine dies and no fuel then ops or lift pump most likely bad. When was the last time you checked fuel filter? You can also check to see if lift pump is operating by putting your hand on the lift pump itself, it should purr like a kitten with engine running, and is located directly below the drivers seat on the inside of the frame.