I'm trouble shooting my 'stuttering under acceleration' problem that has grown into a stallling while going 35 mph problem. (maybe related, maybe not) My question is; Does the OPS supply power to the lift pump with the key in the 'run' position, or does it have to be in the cranking position (engine not running)? If the problem is the OPS, is there any negative to bypassing the OPS and powering the lift pump whenever the key is on, or adding a dedicated switch for the lift pump? Thanks in advance for your thoughts on this.

I could be wrong here, but I believe there has to be oil pressure to the switch (cranking or running) in order to send power to the LP. Its a safety thing. In the event that you flip or roll and the engine stalls or quits, the fuel is automatically shut off (to prevent a fire). Hope this helps,

sshewins is correct on that the only downfall to having it wired to the ignition power supply would be that if you just wanted to listen to your radio or forget the key in then your pump would still be pumping but ya your idea of a switch would work well.

I could be wrong here, but I believe there has to be oil pressure to the switch (cranking or running) in order to send power to the LP. Its a safety thing. In the event that you flip or roll and the engine stalls or quits, the fuel is automatically shut off (to prevent a fire). Hope this helps,

x2. You can put a relay on the LP/OPS to reduce the depedency of LP to OPS but it is still using the Oil Pressure to run the LP. There is a thread on that that link to HowieE who has a schema on how to put the relay or you can get Kennedy Diesel harness.

If you suspect that your LP is not working, you can do the LP test in the FAQ. Better yet, fill out and do the diagnostic checklist also in the FAQ. It will give us all better ways to give you suggestion on how to help you from a distance.

You can take a jumper from a 12v source to the 'G' terminal, lower left of the obdI connector and temporaly power the lift pump to verify it works and this also works great for bleeding air.

Steve

Just crawled out from under the truck. OPS test results... getting power on cranking ONLY. Once it starts, no current at all. Hot wired 12v to pump, sure sounds like it's working. I think I'll locate a 12v source that is on when ignition is on and power it up and eliminate the problematic and almost inaccessable OPS. If I ever have lift pump symptoms in the future, it will be easier to tell if its the pump. I was going to put a switch on the circuit anyway for a WVO conversion. Turn off diesel pump, turn on WVO pump. Maybe I'll get lucky and one fix cures two problems. I'll let you know the results of the T valve test when complete. It was not spitting any fuel on inital test. Thanks, Jim

Got the switch wired in and took it for a lap around the block. Seems to have fixed ths stuttering and staling problem. Thanks for the help. This is a great site. Thanks, Jim

Welcome to the PLACE, Jim!

Careful with that. I got an ass reaming for doing what you did. Bear in mind the LP is wired through the OPS as a saftey feature. If you crash or are invloved in an accident and your fuel line ruptures it will pump fuel into the fire. Of course it is a slim to none chance that all the factors would be in place for that to happen BUT it can happen. I'm going to do the Kennedy Harness when funds permit. I did heed to the warnings I got here so I thought I'd pass it along.

I agree with aces. Sounds like you have a bad OPS, at least the part that gives electricity to the LP. You may want to put a relay on it, there is a old thread here about that. Or buy the Kennedy Diesel LP/OPS harness which may be an easier way.