Oil Pressure Switch

[TTM]

Have a simple question. How do you do a test on the OPS to see if it is working? My buddies 96 is stalling and he had a new IP and FSD replaced 2 yrs ago I would like to rule out the OPS or the lift pump. I have searched the DP for info on a test for the OPS but nothing really clear. Can one of you guys help?

[JohnC]

Open the fuel filter water drain valve while the engine is running. If fuel gushes out and the engine keeps running both the lift pump and the oil pressure switch are working. If the engine stalls, try cycling the key off and back on with the valve open. This should run the lift pump for a few seconds and fuel should come out. If it does, replace the oil pressure switch. If it doesn't, replace the lift pump and retest. (All this presumes the fuse and wiring is all good. Adjust your testing accordingly.)

[TTM]

Thanks John, I will give that a try.

[TTM]

Just a update, did the test all good. Since there was no hard code set I was thinking that it had to be something small. So we started looking at all the wiring from tip to tail, and sure thing there was some wires that under the coolent reservior/air filter houseing that were bare from rubbing. More that likey shorting out there, so re-taped the wires and no codes since. Start small and work your way up as it's been said one hundered times before. Thanks again John for the OPS test.

[gmctd]

Good job, dude - historically, that is a failure-prone area for the main harness.

[robertb6963]

Open the fuel filter water drain valve while the engine is running. If fuel gushes out and the engine keeps running both the lift pump and the oil pressure switch are working. If the engine stalls, try cycling the key off and back on with the valve open. This should run the lift pump for a few seconds and fuel should come out. If it does, replace the oil pressure switch. If it doesn't, replace the lift pump and retest. (All this presumes the fuse and wiring is all good. Adjust your testing accordingly.)

What if you can't get the truck started; fuel won't shoot out when cranking now that i replaced the fuel filter, but it did before so the OPS must be good, right? It ran fine after i put new injectors in three days ago then two days ago-stalling and no start. Also ***Code 45***. Is this code related to the pmd?

[gmctd]

Well, I'm not JohnC, but -

Look over on the passenger-side firewall for a covered area - pull the cover and you'll find the LP START relay and the 20a LP Fuse

Pull the fuse, jumper one spade to the battery, plug the other spade into the fuseholder terminal closest to the fender - lift pump should run freely, pumping lots of fuel out the drain.

If lift pump is vibrating but not pumping fuel, it ain't the OPS

If lift pump is not vibrating and is not pumping fuel, it ain't the OPS

If lift pump is not vibrating but is pumping fuel, you need to call Fox Mulder.............

[JohnC]

Code 45 is an EGR code. Not related. If you crank a '94 with the bleeder open, eventually fuel should come out (and it'll start).

[BamaChief600]

Open the fuel filter water drain valve while the engine is running. If fuel gushes out and the engine keeps running both the lift pump and the oil pressure switch are working. If the engine stalls, try cycling the key off and back on with the valve open. This should run the lift pump for a few seconds and fuel should come out. If it does, replace the oil pressure switch. If it doesn't, replace the lift pump and retest. (All this presumes the fuse and wiring is all good. Adjust your testing accordingly.)


Search can be so helpful....anyway I tried this and my truck died. I know the fuel pump is good b/c I bypassed relay and it pumps fuel up to filter. So off to get a OPS. Can this also cause it not to start when it is hot? I already know I have the dreaded DB4911 and was hoping it would help me not have to fork out the cash for a rebuild.:D Also this is the OPS that Advance has on web site: http://www.partsamerica.com/product_images/img/nie/op6677.jpg. Is this the right one?

[simon]

Search can be so helpful....anyway I tried this and my truck died. I know the fuel pump is good b/c I bypassed relay and it pumps fuel up to filter. So off to get a OPS. Can this also cause it not to start when it is hot? I already know I have the dreaded DB4911 and was hoping it would help me not have to fork out the cash for a rebuild.:D Also this is the OPS that Advance has on web site: http://www.partsamerica.com/product_images/img/nie/op6677.jpg. Is this the right one?

yep that,s the one