Experience with Oil Pressure Switch (OPS) symptoms?

[Adam]

In trying to figure out my stalling problem, I was advised I should replace the Oil Pressure Switch, which sends power to the lift pump. If my OPS is bad, how can I tell? I have read in earlier posts that the gauge will read too low of oil pressure. Mine still seems to read the same pressure it did when I bought it (about 40). Might I still have a bad OPS? :confused:

[arrowheadracing]

I had the same problem. The switch went bad, the pressure read fine. I put a fuel gauge on the tstat housing and cracked it open. I saw no pressure. I thought maybe the guage was bad, so I took it off and left the t-handle open. No fuel drippage. I could hear the lift pump whir now and then so I assumed it was fine. So I bought the oil pressure switch and that fixed the problem. I just had another go bad after 4 months, so now I carry one in the truck with me. You can check the resistance across it, but someone else would have to tell you the #'s to look for.

Todd

[rjwest]

96 and newer usually do not have a OP's problem.

Lift pump runs from a relay powered by PCM.

OP's is in parallel and for and " relay " failure
back up: Cranking engine, 4 psi oil pressure
will energize Lift pump if relay is failed.

Note, OPEN connector, driver side wire bundle,
close to hood hinge for jumping to 12 volts
as a lift pump test point.

Oil pressure sounds good. 40 psi at 2000 rpm " hot "

[Adam]

Thanks Guys. Will test it today.
Todd, what year is your truck? I was told that 99 is the only year that had the "relay" feature. Is it really 96 and newer? Thanks,
Adam

[arrowheadracing]

Mine is a 95.

[rjwest]

All OBD2 96 and newer have a relay...

[Adam]

Thanks again. I seem to have plenty of fuel being pumped by the lift pump and I have not been able to get it to mess up. My wife says it stalled on her three times taking the kids to school yesterday, but today it did not miss a beat. Once it is warmed up, it does not have any issues with stalling. One characteristic of it is that while driving, sometimes instead of actually stalling it will just cough a bit but then it is OK. It seems like a fuel problem. If my '96 should not have the OPS problem, then I guess I had better order a new PMD (Sol-d). Thanks again for your help.
Adam

[CareyWeber]

Originally posted by Adam:
Thanks again. I seem to have plenty of fuel being pumped by the lift pump and I have not been able to get it to mess up. My wife says it stalled on her three times taking the kids to school yesterday, but today it did not miss a beat. Once it is warmed up, it does not have any issues with stalling. One characteristic of it is that while driving, sometimes instead of actually stalling it will just cough a bit but then it is OK. It seems like a fuel problem. If my '96 should not have the OPS problem, then I guess I had better order a new PMD (Sol-d). Thanks again for your help.
Adam Adam,

I'd go over all your electrical connections to ensure that they are in good shape. I found wires going from the engine compartment to the ECM in the cab that were rubbed bare against a AC line that was causing my issue since fixing that mine has not missed a beat.

I firmly believe that lots of 6.5TD pump/PMD issues are related to electrical connectivity issues. I found bad battery cables on my truck even though I clean them annually. Make doubly sure that all your grounds are in good shape.

Carey

[rjwest]

My problem was exactly as yours, Some times
"quit" sometimes " hiccup ".

Always when warming up after about 20 minutes,
( when the temps where around 25-35 degrees)

Went like this for almost a year, would go for months without a problem than do a few " quits '..

Than, on a trip it would have several "quits"
in the morning. Had the injector pump changed.
45K trouble free miles.

Only once did I get a " code" ( Inj Pulse to short".

Do you have less than 120K miles, Warrenty for 120K ,10 years I think.

[HowieE]

The Oil Pressure switch fails because of a design fault. The switch contacts are rated at 1 amp while the fuel pump draws 4 amps. So over time the switch contacts will burn and fail.
The relay mentioned for 1996 and newer trucks does not overcome this problem as that relay is only in the fuel pump circuit during the glow plug cycle to pre charge the injection pump.
To correct the problem if your OPS has not already failed you can install a relay across the switch contacts and reduce the current across the switch to a point that the switch should last forever.
I have posted a diagram of this installation on my web site, address in my signature.

[rjwest]

Howie, The helm's circuit diag. shows the OPS in parrellel with the Relay, They say it is a " fail safe " circuit in case the relay fails. Cranking oil pressure will turn on lift pump.

[Adam]

OK, from what I am hearing, it might behoove me to replace my OPS anyway, since it is only $40 and see what happens? Then, if that does not work, I should spend nearly $600 on a new PMD (or Sol-d) and see what happens; are we in agreement?

I replaced the lift pump and I have pressure coming out while draining the water separator. I have gone over the wires and I can not see any problems or wear spots. I have gone to a mechanics shop and had the computer trouble codes checked (no codes showing at all). My oil gauge never fluxuates or appears to be faulty.

We filled up three days ago, and the car has not stalled once since having a full tank. Hmmm, what does that mean? :confused:

Thanks again guys for your thoughts. I really am starting to wonder how much it would cost to go to a mechanical injection pump.

Thanks again.
Adam
(Shell Knob, MO)

[rjwest]

I doubt the OPS will fix the problem,

When you shut the engine down, the lift pump will run for a few seconds ( untill oil pressure drops )
You should be able to hear it/ feel it when someone shuts off the ign. If it keeps running, it ain't the op's

Could be lift pump, have you checked the pressure with a gage?

My opinion, You need a remoptre PMD and a Spare if you want reliability.

[MTTwister]

"We filled up three days ago, and the car has not stalled once since having a full tank. Hmmm, what does that mean?" -

Maybe you've been dealing with a load of bad gas ( oops - Fuel) all this time.

Howie's OPS Relay still might be a good extra measure of comfort for the OPS contacts.

[Francois]

Pete Sutsos, Bob Triebel, HowieE, Guys,

I am really looking at minimising failure specially engine shutdown because without AC my family (kids) could be seriously in trouble where I am with quite high temperature and miles/days from basic supply and recovery in general.

I read that even later then 96 models should reasonnably make the OPS modification like the http://www.thedieselpage.com/features/sutsos.htm or http://mysite.verizon.net/vze54tx9/ - Both looking similar to me.

I had been taking my GM workshop through many non orignal modifications but I cannot get them to make the relay for Oil Pressure Switch this time. I am not good with electronics and cannot take risk considered my low knowledge.

Can anyone volunteer to make one tested kit to fit my 1997 Suburban - I suggest to pay back using Paypal or Visa.
I can be contacted on this forum or thanks to TDP.

Thanks for your attention.
Francois Dorleans

6.5TD Suburban 1997 K2500 4WD full float 4L80E
+Toq lock+Exhaust brake+SOL-D+265/75R16 Michelin

[Adam]

Would it hurt anything to supply power to the lift pump simply from the ON key position? I know it would run during the glow cycle and would run while the engine is off and the key is on, but I can't see how that would hurt it. Can anyone else see a problem? That way, we get rid of the OPS having anything to do with it. I know that the OPS is supposed to shut off the pump in the event of oil pressure loss, but will that really stop the engine? I have read many times that the engine will still run without the lift pump working anyway. What do you guys think?
Adam

[BobND]

Adam, I believe the oil pressure switch is designed to shut the fuel pump off in the case of a rollover or crash, to hopefully lessen fire danger.

There is NO reason from a cranking or glow plug, or IP standpoint that the fuelpump could not be running at all times when the key is "ON".

If being broke down in a desolate place is a concern, there is no reason why a simple toggle switch can't be wired in, to provide power to the fuel pump in case of sender failure, to get home with the truck.

When I got my '94, the PO had set it up with a couple of quick disconnects under the hood, near the wiring feed-through on the LH side of the firewall. Unplug the fuel pump from the original wire, and plug it into the other wire, fed "ignition on" power through a fude, and the FP runs as long as the key is on.

That's simpler than the other mods, and will get you home, but is not as "wife-friendly" as a toggle switch!

[rjwest]

Adam, Does your suburban Have OBD2 or OBD1
I assumed it to be OBD2, It is important to now this before you decide what action is required.

(I presummed that all 96 gm were OBD2 compliant.)

If you are REALLY concerned about fuel lift punp operation. Add a fuel pressure gage to the dash instruments..

[Adam]

Mr. West:
I do not know if I have OBD1 or 2. I unfortunately have not read enough on these boards to ever figure out how to tell which one I have. How to tell? Thank you again for all your help.
Adam

[rjwest]

email me with your phone number , I'll try to help.
qwestav@attglobal.net