About 2 weeks ago the oil pressuring te on my 95 chevy 2500 s vin turbo diesel jumped from 40 pounds to around 60 pounds accordo the gauge. I found the oil pressure gauge would read anywhere between 40 and 60 pounds. After doing research on this site and others I decided that the oil pressure switch was most likely the problem. The snap on truck was in town today so I picked up the socket I needed and stopped by napa on my way home and bought a new oil pressure switch. I installed the switch without too much difficulty. The truck started normally and I took it for a short test drive. The oil pressure gauge showed 40 pounds. The truck would not shift out of second gear and even worse the truck would not shut off when I turned the key. When the key was in the off position the tac wold go to 0 but the engine was still running. I then put the old OPS back into the vehicle and everything was normal except the oil pressure was varying. I went back to napa and exchanged the ops for a different one. I installed the second ops and had the same problem where the truck wouldnt shut off.

Thanks for the help I am all out of ideas.

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Problem: Explain your problem in concise language (ie: Cranks but won’t fire). ____________________________

Demographics: tell us about your truck and your ambient conditions:

- Year:1995
- Truck model and class (ie: c2500) k2500
- Automatic or Standard Auto
- Mileage: (indicate miles or km) 176,000
- Replaced parts and mods (IP, PMD, chip/PCM, TM, injectors etc) PMD relocated
- Model: ‘S’ or ‘F’ engine, NA or Turbo, EGR? S
- Ambient outside temp: (indicate *C or *F) 40* F
- What fuel are you using? (#1 Diesel, #2 Diesel, Bio, VO, WVO, etc) diesel
- What fuel additives are you using? none
- Where are you located? Indiana

General maintenance: inspect and evaluate the condition of each. When were they last changed?
- Air filter 3 months
- Fuel filter 6 months
- CDR Valve? unknown
- Coolant – last flushed/replaced at unknown
- Oil – synthetic/regular, changed at 3500 miles age
- Batteries – state of charge, (matched set) replaced at unknown
- Battery cables and grounds (removed, cleaned and tightened): today
- Glow Plugs - how many miles on them? unknown What type? unknown
- Injectors - last changed at unknown


History: (Describe how the problem first appeared.)
- What were you doing when it happened? see post above
- How was the truck running fine before this problem appeared? fine
- Has this problem ever happened before? no
- Describe any related factors that might be part of the problem. see post above
- Have you checked for DTC (Diagnostic Trouble Codes)? (Y.N) yes And? none

Diagnostics:

1] Starting:
1a] Does the engine start? _________y
1b] Does the engine crank over? ________y
1c] Are your batteries fully charged? _________y
1d] Have you removed, cleaned, and tightened all battery connections? ________y
1e] Does your Wait to Start light come on for a time? How long? n/a
1f] Does your glow plug light come on? __yes_______ For how long? ___7-10 seconds______
1g] Do you see smoke from the exhaust while cranking? What color? _yes white_______

2] Fuel Issues (if not running):
2a] Can you hear your lift pump working? _____yes_______
2b] Do you get a steady flow of fuel from the water drain (T-handle) ? ___unknown______
2c] Loosen the inlet line from the IP – is fuel coming out (Lift Pump on)? __unknown_________
2d] Loosen an injector line and crank the engine - does fuel come out? __unknown_______
2e] Do you hear a vacuum (hiss) when you remove the fuel cap? __no_________

3] PMD / IP Issues
3a] Location of PMD (on pump, on intake, remote mounted) _behind front bumper__________
3b] Condition of Extension harness (if used) Vendor or Homemade? __vendor_______
3c] Condition of grounds / ground wires to IP / PMD. Check Harness. ___good______
3d] PMD Make: stanadyne
3e] PMD Age: unknown

4] Stalling Issues N/A
4a] Do you experience stalling only when hot?
4b] Does it stall under particular circumstances? (ie hit bump, or on accel) ______
4c] Does pouring cool water over the IP seem to help with restarting? _________
4d] Is stalling momentary (engine recovers)? _________
4e] Does SES light come on when engine hiccups? _________
4f] Does cruise control quit working when engine hiccups? ___________
4g] Does re-starting seem to reset engine, restoring cruise and power? _________
4h] Changes to dash lights or instruments during stalling events? ___________

5] Running Issues
5a] On cold start, does upper rad hose get hard before engine warms up? unknown
5b] Any bubbles or oil film in coolant overflow tank? no
5c] Any white slime on oil surfaces (dipstick, CDR, oil Fill cap)? no
5d] Excessive white smoke from exhaust on cold start? no
5e] Excessive black smoke from exhaust under hard acceleration?no
6] Performance Issues
6a] Do you have gauges? yes
6b] Maximum boost under load? ____________unknown
6c] Have you added a performance PCM (reflash) or Chip? ______________ no
6d] Have you changed exhaust / downpipe / crossover? ________________ yes
6e] Wastegate – mechanical or vacuum? ______________ vacuum

7] Temperature-related Issues: n/a
7a] Single or dual thermostats? ____________
7b] Have you replaced them lately? Manufacturer of replacements? _________
7c] Have you pulled and cleaned Radiator and coolers lately? ____________
7d] Have you replaced the fan clutch? Manufacturer of replacement? ________
7e] (winter) Have you tested your antifreeze? Good to what temp? __________
7f] (winter) Are you using a winter grille cover? ___________

 

what brand ops

 

Hmmmmm.....that's an odd one.

None of that makes sense with just an OPS change.

The OPS powers the lift pump (except while key is in "start" position, unique to 95 models only) as well as drives the gauge on a 95 , but it doesn't keep the engine running after a "key off" event.

I'm going to guess it's actually an ignition switch problem.

here's a pic that will make the rest of this post a little "clearer":




You might think that and OPS keeping the lift pump running might keep the engine running if it fails on shutdown.

But, the key shuts off the the Fuel shutoff solenoid and the PCM shuts down the PMD, which no longer drives the fuel solenoid once power is removed from the PCM (IE: key off). The fuel solenoid is what determines the injector pulse to the cylinders. Stop driving the fuel solenoid and there's no fuel delivered to the cylinders.

Remove power from the PCM/fuel shut off solenoid and the engine will stop. No questions asked as the FSOS is powered open. Remove the power and the FSOS slams shut, cutting off fuel to the IP.

Somehow, you're still getting power to the PCM/FSOS which leads me to say "ignition switch". That seems to be the only common point of failure in the systems you're having troubles with.

The ignition switch is very "glitchy" on GMT400's when they get old and worn. I'm going to guess your OPS change/no shutdown problem is a coincidence.

Now, if someone has messed with the wiring, all bets are off...something very "weird" could be going on and power going where it's not supposed to.

Keep in mind; without actually seeing and troubleshooting the truck, I'm guessing here....

 

I only use AC Delco or GM for the OPS. & many other parts. They seem to hold up better.

Did you have any voltage coming off your old OPS?

I did the dual lift pump relay upgrade and the voltage coming off my bad OPS was enough to engage the relays and run the lift pump. I've been meaning to change the OPS just because but it's been running this way for several years now.