1996 K1500 Suburban shifting funny / cutting out

[jrsavoie]

The new accelerator pedal did not fix my issue.
The transmission acts like it is down shifting.
The shop that has the 1996 K1500 Suburban does not know 6.5 diesels.
I took it there because they had previously rebuilt the transmission. And I thought it might be a transmission issue.
They said they thought the IP was quitting momentarily.
Any ideas on what to do for diagnostics. I am going to see if I have a different PMD extension harness. If not I will order one from Leroydiesel Leroy.
I know I have more PMD's.
Could it be the optic sensor?
I am almost positive I have removed the optic sensor filter harness on that vehicle. and plugged directly into the IP

I am wide open to suggestions

 

[ak diesel driver]

Do the sensor tests

 

[jrsavoie]

Do the sensor tests

What exactly are the sensor tests?

I searched it, but got no results

The Suburban starts easily and runs fine at idle.

I noticed the shifting issue mostly above 45 mph. I haven't had squat for time to look at it. I rarely drive it. It's my daughter's Burb.

From what I have gathered, the sensor tests amount to unplugging the sensors and running without.

"Try unplugging the CPS (crankshaft position sensor) and starting. It will take quite a bit of extra cranking and will start in limp mode. If it runs smoothly then that tells you the CPS is bad. You can do the same thing with the optic sensor."

Since I do not notice the Suburban's issue at idle, will these tests work driving down the road? From what I gathered the burb would be running in limp mode with either of the sensors unplugged
Thank you much

I would have replied much earlier, but ISP went down and computer locked up, shortly before my original post

 

[Paveltolz]

Do you feel the 'IP quitting momentarily?' Seems like that would be apparent at about any speed. Certainly under acceleration up to 45mph.
Any codes now? You've been around long enough to know the absence of an SES light doesn't mean there's nothing going on behind the curtains.
Somewhere I recall failing PMD symptoms affecting the Cruise Control's ability to hold speed; is that working?
Grounds again...Check Black/white and Tan/White ground (ECM) near the transmission dip stick, passenger side.
I know you 'don't have time' so refer to the Diagnostic Checklist, look at the questions and see where that takes you BEFORE THROWING PARTS AT IT.
"Almost positive" about pulling the OS filter harness off is a reason enough to check it and everything else since you can't really be sure about anything at this point. Not being judgemental, you said it's your daughter's DD so, since it isn't your ride, you got to get in there and be certain
Consider: Winter Fuel; Age of the injectors; last fuel filter changes; additives she's using (yeah, I know, daughter's ride so probably none); condition of the PMD harness (fouled inside); how's the condition of the IP harness ground; other grounds like the one mentioned above; transmission fluid age...levels....
Don't envy your having to do this in Illinois in December. 31* with 10 mph winds and 74% humidity doesn't sound bad except it feels like -2...gotta be unpleasant.

 

[jrsavoie]

No codes with my cheap code reader and no check engine light.

Cruise control seems to be working just fine.

Fuel filter is changed at every oil change.

The burb is 60 miles away at the shop it was taken to for the transmission issue. They diagnosed the trans issue to be caused by the current issue.

They said the trans was building excessive pressure for some reason.

I am working on her porch - 30 miles the other way.

I have her dining room loaded with drywall and siding. We are running out of weather fast and I was not feeling well last week.

I could survive only having to worry about one but both is a bit overwhelming. Not to mention all my own stuff that isn't getting done. LOL

I am going to print the checklist and give it to them when I drop off the extra stuff I have here - PMD's extensions, hopefully a Mapp sensor.

 

[jrsavoie]

I never drove it hardly at all, other than to say it definitely needs work - I thought it was a transmission issue.

If I remember right if you got on it from a stop it would rev and run , but not necessarily shift at the proper times. I had to let up on the fuel to get it to shift sometimes. But i DID NOT NOTICE IT CUTTING OUT except when cruising.

You may just be shocked to hear that other people didn't notice it doing anything exceptionally bad. LOL

 

[jrsavoie]

Problem: Explain your problem in concise language (ie: Cranks but won’t fire). ___Thought ti was a transmission issue do to shifting funny. The real issue caused the transmission issue._________The Suburban is cutting out and causing excessive pressure in the transmission________________

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

- Year: _1996_____
- Truck model and class (ie: c2500) __GMC K1500 Suburban_______
- Automatic or Standard _____Auto_____
- Mileage: (indicate miles or km) _350,000 miles________
- Replaced parts and mods (IP, PMD, chip/PCM, TM, injectors etc) ___________
- Model: ‘S’ or ‘F’ engine, NA or Turbo, EGR? _____F eninge_________
- Ambient outside temp: (indicate *C or *F) _All temps_________
- What fuel are you using? (#1 Diesel, #2 Diesel, Bio, VO, WVO, etc) _All fuels____generally 11% bio____
- What fuel additives are you using? ____Schaeffer’s mostly_______
- Where are you located? 60927_____________

General maintenance: inspect and evaluate the condition of each. When were they last changed?
- Air filter ___ last oil change ______
- Fuel filter _____last oil change____
- CDR Valve? ______unknown___
- Coolant – last flushed/replaced at _______maybe 300,000______
- Oil – synthetic/regular, changed at ___Synthetic every 10,000 miles________
- Batteries – state of charge, (matched set) replaced at ____good_________
- Battery cables and grounds (removed, cleaned and tightened): ____unknown__________
- Glow Plugs - how many miles on them? __unknown_______ What type? __AC Delco 60G___________
- Injectors - last changed at ___230,000 miles___________


History: (Describe how the problem first appeared.)
- What were you doing when it happened? _______I think it has been ongoing for a while. Long enough for the chugging to take out the transmission_______
- How was the truck running before this problem appeared? ___ fine __________
- Has this problem ever happened before? __________I am guessing it has been happening since the trans went out the first time. But at 300,000 miles plus the trans could have just gone out the first time_____________
- Describe any related factors that might be part of the problem. ______________
- Have you checked for DTC (Diagnostic Trouble Codes)? (Y.N) __Y__ And? ___No results with my cheap code reader_____

[FONT=&quot]
[/FONT] Diagnostics:

1] Starting:
1a] Does the engine start? __Yes_______
1b] Does the engine crank over? _yes_______
1c] Are your batteries fully charged? __yes_______
1d] Have you removed, cleaned, and tightened all battery connections? ________
1e] Does your Wait to Start light come on for a time? How long? normal_________
1f] Does your glow plug light come on? _________ For how long? ___normal - starts great______
1g] Do you see smoke from the exhaust while cranking? What color? ________
1h] Does the Service Engine Light Glow during Start/bulb check? ________

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) ? __last I checked_______
2c] Loosen the inlet line from the IP – is fuel coming out (Lift Pump on)? ___________
2d] Loosen an injector line and crank the engine - does fuel come out? _________
2e] Do you hear a vacuum (hiss) when you remove the fuel cap? ___________

3] PMD / IP Issues
3a] Location of PMD (on pump, on intake, remote mounted) ____in bumper on a heat sink_______
3b] Condition of Extension harness (if used) Vendor or Homemade? ____Vendor made in the USA_____
3c] Condition of grounds / ground wires to IP / PMD. Check Harness. _________
3d] PMD Make: ____Flight Systems_______
3e] PMD Age: ________Fairly recent_____

4] Stalling Issues
4a] Do you experience stalling only when hot? ___No stalling_________
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? _____N__
5b] Any bubbles or oil film in coolant overflow tank? __ N _____
5c] Any white slime on oil surfaces (dipstick, CDR, oil Fill cap)? _______N___
5d] Excessive white smoke from exhaust on cold start? ______ ___
5e] Excessive black smoke from exhaust under hard acceleration? __________

6] Performance Issues
6a] Do you have gauges (boost, EGT) ? _______ N ____
6b] Maximum boost under load? ____________
6c] Have you added a performance PCM (reflash) or Chip? ___NO___________
6d] Have you changed exhaust / downpipe / crossover? __Don’t remember______________
6e] Wastegate – mechanical or vacuum (OEM)? ___OEM___________



List and describe any other factors which are not addressed in this checklist. We can’t see, hear, smell, or touch your truck, so the more descriptive information you can give, the more likely it is that somebody can assist you.

_________________________________

 

[ak diesel driver]

Sensor test is simply that a test. I can run pretty normally with one of them not working 100%. If it gives you any issues at all during testing then that sensor (or related wiring) is suspect.

 

[jrsavoie]

Sensor test is simply that a test. I can run pretty normally with one of them not working 100%. If it gives you any issues at all during testing then that sensor (or related wiring) is suspect.

You have to be very specific for me. LOL

So what you are saying is unplug the CPS and run. if it runs without hick-upping that indicates the CPS is the issue causing the hick-ups. Same with the Optic sensor.

I thought the vehicle would go in limp mode with the sensors unplugged

 

[ak diesel driver]

It will go into limp mode but it will be running on one sensor instead of two. Just a tool to help eliminate things.

 

[jrsavoie]

It will go into limp mode but it will be running on one sensor instead of two. Just a tool to help eliminate things.

I am more than a little dense sometimes.

Not sure what I am supposed to be looking for when I unhook either sensor. It starts easily and seems to idle fine.

If I tell them to unhook a sensor what should they expect if the sensor is good or bad?
Can the optic sensor be changed or is that a pump issue?

If I had the vehicle here, I would probably just replace both sensors as they have over 300,000 miles on them and were probably made in 1995.

How much do the sensors cost? Would it be cheaper to have them replace the sensors than try to diagnose them?

It looks like the CPS would be just as cheap to have them change as diagnose.
Is AC Delco the way to go for $50?

https://www.amazon.com/gp/huc/view.html?ie=UTF8&newItems=Cf2425abb-bf29-440b-bdbf-9f0d724a7c85,1&tag=jhdiesel-20

Optic Sensor Stanadyne: 33883

 

[ak diesel driver]

If it runs smoothly and normally then it tells you the sensor is working. Try both sesnsors and if it runs fine then you have eliminated them as problems. Should be able to test both of them in 10 minutes or so. Don't know if it would be appropriate to try driving it while doing this or not.

 

[jrsavoie]

Disconnect the optical sensor connector from the injection pump. This is the large square black connector directly on top of the injection pump. Again try to start the truck. If the truck starts and runs, this means that the optical sensor is outputting faulty data preventing the truck from starting. By unplugging the sensor, you put the system into backup mode and the computer relies on information from the crankshaft position sensor. In the very unusual case that both sensors were bad, the truck would not start with the optical sensor disconnected.

I am still not grasping how this test should be done to tell me anything about what I am trying to find out. The burb starts and runs fine until you are going. Then it stumbles. Will unhooking the optic sensor remove the stumble if it is causing it?

 

[jrsavoie]

Can the optic sensor be changed or is that a pump issue?

If this shop does not figure it out soon it will go to the local diesel shop that has more experience with 6.5's

 

[MrMarty51]

Try unplugging the PMD, put a different PMD on the end of the harness and see what it does.
I dont think I would try running a PMD that is not attached to a heat sink for very long due to the heat, but it should be okay for a nice test run.
Then when the extension and sink get to you from leroy, it can then be installed proper.

 

[jrsavoie]

Try unplugging the PMD, put a different PMD on the end of the harness and see what it does.
I dont think I would try running a PMD that is not attached to a heat sink for very long due to the heat, but it should be okay for a nice test run.
Then when the extension and sink get to you from leroy, it can then be installed proper.

Ended up ordering from Quadstar. I think they are tied with Leroy. I never heard from leroy this morning and had to get ordered. I should have been out of the house hours ago.

I sent 4 pmd's mounted on heat sinks. One gray, one new and one off the Tahoe. My spare extension cables and injection pump harnesses looked like they left a little to be desired. But I sent them also. I have a couple of short harnesses that they can plug a PMD on heat sink into for testing

 

[ak diesel driver]

It should run perfectly on one sensor, if it has any hiccups or stumbling or anything else off, then the sensor needs replacing. If you have an intermittent sensor it is more likely to show up when it's the only one in the loop

 

[WarWagon]

Try unplugging the PMD, put a different PMD on the end of the harness and see what it does.
I dont think I would try running a PMD that is not attached to a heat sink for very long due to the heat, but it should be okay for a nice test run.
Then when the extension and sink get to you from leroy, it can then be installed proper.

Never ever run a PMD without a heatsink. They immediately overheat and the heat damage is done - if they continue to work at all. The amount of power the PMD dissipates was a design screw up all the way around.

 

[WarWagon]

Sounds like the engine is cutting out and this can cause a downshift. At the minimum the TCC will unlock and then lock back up when the engine is running ok again. Fishbite is the term you are looking for for a single miss that you feel.

It's possible you have air in the fuel system, gelling fuel... What's the lift pump PSI at the water drain now, how old is the fuel filter, and is the fuel heater working? Water at fuel drain? Fuel smell like gasoline?

 

[Will L.]

Ok I would like to jump in and reword what AK is saying -no offense, I think it is just getting complicated.

To do the test. It will be hard to start, may take 15- 20 start. Once it starts and revs up, turn it off- no test drive needed. Any misfire afterwards is irrelevant.
1. Tell them unplug the cps and try to start it.
A. If it doesn’t start, the optic sensor is bad.
B. If it starts the optic sensor is working.

2. Plug it back in. Unplug the optic sensor.
A. If it doesn’t start, the cps is bad.
B. If it starts the cps is good.