loosing power to the transfer pump

[andrew8279]

I'm working on a 1995 c3500hd. The engine is stalling after a minute from when started. The farthest I got was I only have power at the fuel transfer pump on the chassis rail while cranking, but when the engine starts the power is lost. There is a relay that controls the pump only while the engine is cranking, it is powered through the crank fuse(per schamatic). After the engine is running there is no more power at the crank fuse and the PCM takes over the power. I just don't know how. I replaced the injection pump driver and that didn't work. If anyone has any ideas.

[a5150nut]

Oil pressure sensor at the rear of the valley, behind the fuel filter. It takes over by pressure when you quit cranking and stops in case of power loss in an accident. Least that is how it works on my 94.

[Patrick m.]

This is one of the week circuits on this truck. the lift pump draws too much current for the ops to carry, and causes the ops to fail. There is a good fix though, all you do is replace the ops, wire it so that it operates a relay instead of the lift pump the relay then feeds power to the pump.
Almost any relay out there is better able to carry the current requirements of the pump.

There is even a diagram showing exactly what to do on here somewhere.

[Robyn]

This system was replaced with a better setup in 96.
Just installing a new oil pressure switch will most likely get you going fine again.

I have seen many of these switches go 200K plus and others fail right out of the gate.

The contacts are fairly small and as was mentioned realy cant take the current over the long haul.

Best

Robyn

[ol9465er]

If you look on the Members Page there is an instruction and diagram for installing a OPS relay. I did mine four years ago after replacing two OPS and have never had a problem since.

[andrew8279]

Thank you for your help with my transfer pump problem. It was the OPS. The worst part is I have a lot of experience with chevy 350's and I knew about the power going through the OPS. I just didn't think that it would be wired to the transfer pump on a diesel. It didn't help that the schaematic in the chilton I have did not show the power going through the OPS. The important thing is it is running, now I can go fix something else. Thanks again.