Lift Pump circuit

[94K30]

I am having trouble with the lift pump circuit. I have installed new Lift Pump, new Relay, and Oil Pressure sender, and pump is still not working. Today, I tested relay harness for Ground, at connection D,it was OK, I got 12 V at terminal A etc... Moved on to Pump harness, did not have 12 V there, Ground was good. At Oil sender, I bridged out the 2 terminals there, and pump ran. Would this mean that sender is bad, even though it is new? Are there any other possibilities? :confused:

[grancito]

Pull the plug off the OPS and put a paper clip between the two outer connectors of the plug. Pump should run with the ignition switch on, engine not started, if not, look for lack of power from the ignition switch to the relay.

[94K30]

Hi Grant, I did that, and it does run. The question is : does that mean the sender is bad even though it is new? ( from NAPA) Is there any other possibilities? Thanks

[grancito]

Sounds like the sender is bad or you have no oil pressure. When mine fails I am going to connect the two wires. The function of the switch is to shut the pump off in the event of a crash.

[94K30]

That's what I was thinking..... I have good Oil Pressure, 30 to 40 Lbs when warmed up, a lil higher cold. I think I will try a OEM sender first. If you connect the 2 wires there, your pump will run all the time, you would have to run a lead from a switched Ignition circuit to the pump to have it run only when the ignition is on.....
and again, thanks for your responce...
Marc

[grancito]

Oh yours runs with the ignition off when jumped, like mine, thought someone had modified mine, so yes another OPS is the answer.

[94K30]

Oh yours runs with the ignition off when jumped, like mine, thought someone had modified mine, so yes another OPS is the answer.

too Bad they are such a pain to reach, huh? The only way I got the last one out was with a basin wrench..... this one should be easier...it hasn't been in there long.

[synthetic-oil]

too Bad they are such a pain to reach, huh? The only way I got the last one out was with a basin wrench..... this one should be easier...it hasn't been in there long.

I bought an OPS socket at autozone for less than 10 bucks

[94K30]

Yesterday, I changed the OPS for a AC Delco one, and still no luck.... does not work. I talked with a buddy that is a Marine Mechanic and he sugjested it was the connector at the OPS. That makes sense that it would work bypassed with wire, but not when hooked up, as the contact points have lost their springiness and are not making contact. I looked at the sender I just took out, and the center contact is bright and shiny, but the other two for lift pump curcuit are tarnished, like they did not contact anything. Local auto parts store is transfering in the connector, will be here this afternoon.... I will post results.

[94K30]

New OPS connector spliced in, and Low and Behold, the Lift Pump Works!!!

[christja]

Im recently having trouble with my lift pump. I installed a new pump and it still didnt pump. I have power at the pump connector. I took the pump out and bench tested it, and it just humms, not like the pump is working, more like its grounding out. Could the brand new pump be bad? or should i check other things before i replace it?

[JD_countryboy]

My new pump hummed when not pumping fluid either. Change your OPS. GM bulliten my uncle found told that even though you get 12 volts at the connector, the OPS, if bad, will not let enough current thru to operate the pump. It takes current to operate the pump, not just the power. Hope this helps.

[christja]

Checked out the relay. I jumped from terminal 30 to 87 and the pump runs when the key is off...so i figgure the relay is bad. I got a new relay and its still not working. Does the OPS send power to the relay then to the pump or does it send power to the pump and the relay controls the ground? Im half tempted to install a switch and line between 30 and 87 and just turn the pump on by hand before i start the truck...any thoughts on that idea?

[JD_countryboy]

Relay supplies power while cranking truck to start. you let off the key the OPS keeps the pump running. The relay and OPS are independant of each other. With the key on, Try jumping across the terminals on the ops connector, if pump runs then its the OPS.

[christja]

While it may be the OPS...Ill check tomorrow i hope. Is there a problem with just cutting that OPS (or is it POS??) out of the equation by installing a manual switch in place of the relay?

[JD_countryboy]

That is not recommened. Cause in event of am accident, there would be nothing to shut power off to the pump and it would keep pumping fuel. If a fire would occur, youd be fueling a fire. OPS would cut power if engine shut down. That has been mentioned in another post someplace.
I had the exact same problem as you, it was OPS. They are prone to failure. just like the pmd's.

[christja]

I replaced the OPS switch about 1 year ago with the HD one walt sells that "fixes the problem of switch failures". Does anyone know why this switch is prone to failure?

[94K30]

The contacts in it are small, and it is running the power to the pump through it. I have heard of guys rewiring it with a relay to take the load off the contacts.... But on mine, I fount that the connector itself was bad, not the sender. the female pins in the connector had spread out and were no longer making contact with the sender on the connectors for the pump (I still had reading for gauge) when I changed out the connector, it cleared right up.