My LP is not working, but It works with a 12V jumper. I read 12+ volts at the LP connection with the truck running and all the connections hooked up. Im down to the OPS. Im not one for just throwing money at a problem w/o being sure what it is. I was testing the amps to the LP after reading the FAQ about having too much resistance in the OPS. With the truck on and the connector on the OPS I read 1-1.2 Mamps. With a 12V supply to the OPS connector down to the LP I read 2.4-2.6 Mamps. Is this enough of a reduction to cause the LP not to work? Any help appreciated. Matt

When was the OPS changed last?

I dont know if it ever was replaced. 213K miles on the truck.

My LP is not working, but It works with a 12V jumper. I read 12+ volts at the LP connection with the truck running and all the connections hooked up. Im down to the OPS. Im not one for just throwing money at a problem w/o being sure what it is. I was testing the amps to the LP after reading the FAQ about having too much resistance in the OPS. With the truck on and the connector on the OPS I read 1-1.2 Mamps. With a 12V supply to the OPS connector down to the LP I read 2.4-2.6 Mamps. Is this enough of a reduction to cause the LP not to work? Any help appreciated. Matt

If you REALLY want to know what is going on with the OPS, try measuring the voltage (tapping in) at the lift pump connector with the truck on AND THE PUMP CONNECTED. This will tell you if you have burnt contacts in the OPS.

The OPS can provide adequate voltage without load with burnt contacts, but much like a bad battery cable connection will fall "on its face" when load is applied...

The real truth of the situation is that replacing the OPS should be a maintenance item and should AT LEAST be changed whenever the lift pump is changed. The part is just too inexpensive and too critical NOT to change out.

Regards,

The simplest thing to do is consider it bad and be done with it. Replace it and plan on replacing it again. Control the lift pump with a home made relay setup OR we make a complete harness that takes care of most everything for you.

I dont know if it ever was replaced. 213K miles on the truck.

You can do what Goldsburg suggested. In my case, I have one of the Kennedy harness, it has been working very good. Since it uses a secondary OPS, I don't need to change the main OPS again. It also has a prime button so I can run the LP just by pressing the button. But if you just want to replace the OPS, it is not too expensive. Kennedy also have those or you can go to the local part store. Make sure you get an AC Delco original not the store brand.

Does the kennedy harness cycle the pump before cranking and for how long ? That was my biggest gripe with factory setup.

15 seconds. It comes with a fuse tap that I connect to the GP fuse ("Hot" when key is on).

I measured the current needed for the factory lift pump @ 1.85 amps, in case that helps.

I measured the current needed for the factory lift pump @ 1.85 amps, in case that helps.

Possibly, but his readings were milliamperes????!!!??!?!??!?!?!!?!??!??!?!!?!?

Could THAT indicate a bad OPS......?

Regards,

When I wired a switch to my LP I put a light on the switch bracket. I tapped into the LP fuse lead on the firewall. Light glows no matter what method powers the IP. Main purpose was filling the filter housing when changing filters or powering up the LP if the OPS pooped.
I noticed last time the OPS pooped that the light by the switch flickered rather than giving a steady glow. So, the way I see it, the light is pretty much an indicator of OPS health. Last time it flickered a little, I unplugged the OPS and plugged it back in and went back to steady bright light. I guess the plug got a bit dirty.
Ted

I went ahead and replaced the OPS with an AC Delco unit. Now the LP is working fine. It also quit stumbling under hard acceleration which it had been doing lately. At least no stumbling for the 15 min of flogging that I gave it tonight. So Im not too worried about modifying my wiring.
As for milliamps or amps, I tried both settings on my crappy craftsman multimeter and could only get a reading at the milliamp setting. I may have been reading it wrong since my original reading was under 1.85. And the working reading was over 1.85.
So I guess that my truck was another case of 12V at the LP when the connector's unplugged and no working LP when Its hooked up. BAD OPS Thanks for the help again. matt

Cool, glad you get it done.

Possibly, but his readings were milliamperes????!!!??!?!??!?!?!!?!??!??!?!!?!?

Could THAT indicate a bad OPS......?

Regards,

I don't know, Goldsburg, I read them to be MEGAamperes!!!!:)