Lift pump vs OPS

[big61fourby]

Man, I just can't leave well enough alone...

Thought I'd crack the water drain open, check for water and see if LP is working. Got nothing. Not even a drop. Closed the valve, motor dies. Crank, won't even sputter. Check for voltage to pump, key on, 12.6 volts. Did I read somewhere that the IP actually has an internal pump that will let the motor run, even if LP fails, or was I dreaming?

I'm really thinking this is the pump, but how can I rule out the OPS? The switch should only take over once the motor's running, right? So it should at least run w/ a bad switch, then die? Going to the store first thing for parts, any reason not to go ahead and change the pump? Thanks

[opto]

You can check if Pump is working by connecting a fused "hot" wire to the lower left contact in the service connector under you dash, little left from the steeringwheel

It is not cuncommon for the pump relays to fail

[moondoggie]

Good Day!

[i]

[Barry Nave]

Nice thing on our 95 is that we can also put in drive,turn key to start and the lift pump will run. Nice for filter change. 96,lift pump should run when cranking.

[big61fourby]

Thanks for the input. Picked up a pump (Carter, from Oreilly's, lifetime warranty) this morning, problem solved! Now I know what the LP is supposed to sound like. I never heard the old one in the few months I've owned this truck. Changed the filter while I was at it, tons of crud in the bottom, and the filter was very black. So how much damage has the IP suffered from this lack of preventative maintence? I am begining to think a filter before the LP is a very good investment...

[rjwest]

As I read post, you have a 96, OBD2.

I do not think ops is problem, as lift pump is controlled by PCM, On momentarly for a few seconds, than on contimuesly when PCM senses rPM

There is a TEST wire, under hood by left (driver side) hood hinge, look for a red wir with a connector, not connected to anything ( its in the wire bundle).
Jumper to 12volts to test Lift pmp,
If it runs than the relay is next possibility..


Also , the OPS will operate the lift pump
if relay fails, ops sends power when oil pressure comes up.. There fore if lift pump not runnunig
when eng is running, it is eithier,
Lift pump, connector, relay wiring, or bad ground wire..

[big61fourby]

So rj, if I read you correctly, the full amp draw from the lift pump does not run through the OPS on this truck?

The OPS upgrade kit from Kennedy looks pretty sweet, but is it really a necessary upgrade, as it only tells the PCM what the pressure is, and doesn't send power to the lift pump?

[rjwest]

As I read the diagram, Lift pump is already powered by relay before oil pressure switch provides parallel circuit, On shut down the relay opens but OPS sw keeps lift pump running untill oil pressure drops. It appears the relay , by powering the lift pump ON keeps the OPS from burning out,.
I do not recall many OPS fails on 96 and newer.
( A Little Here Help Guys !!)

I am not educated on Kennedy kit, I thought it was mainly for the 95 and older , to power the lift pump from a relay, there by unloading the OPS of high starting current.. Best let him explain what it does for 96 model.

I installed a Fuel pressure gage on the dash, One of the best gages, Imediate knowledge of fuel supply system, also a good MPH/HP gage, as fuel pressure drops, milage goes down..

You can test OPS by pulling relay and starting truck, lift pump will come on as pressure comes up. ( thet is if lift pump is working )

Hope this helps,
Note: If you have a Lift pump concern, find the test wire ....makes trouble shooting much easier..