1998 6.5 shuts off past 170° f

[Loganshaw_6]

This is my first post on here hopefully it's not a tough one for you guys to help me figure out.
I bought a 1998 Chevrolet c 2500 with a 6.5 in it not running. I was told it would start when cold but not when hot. I ended up replacing the injection pump with an ACDelco remanufactured pump. New PMD (relocated behind the grill with a heatsink) lift pump, ECT sensors, IAT sensor, used good ECM, glow plugs, starter, and batteries. everything has been replaced with ACDelco parts with the exception of the IAT sensor, starter, and batteries. Previously I installed 2 remanufactured pumps from Diesellogic.com first pump leaked, second pump was diagnosed by SMR Diesel in Colfax, NC to have a faulty optical sensor as the truck was losing cam signal past 170 degrees. I now have the AC Delco pump in the truck and it will run past 170 degrees but RPM will fluctuate from 700 to 680 and begin to run poorly. The truck will run past 170 but will eventually cut off on its own or if you try to give it any throttle. If you keep the RPM above 1000 the truck will run but if you let off it will die. I'm using a Snap-On Solus scanner to set timing. TDC offset is at -0.46 with time set enabled my desired timing is at 0 and my actual timing fluctuates from 3.5 to 3 3.8. I have been reading forums trying to understand how the truck works and make sure I set timing properly. I believe I am doing it correctly but please let me know if there's something I am doing wrong as this is my first 6.5. My truck has a factory EGR my new used computer came off of a truck without an EGR. I relearned to the computer and got a security light to go away. The truck still has the same problem as before. The truck runs great it starts right up cold but once it reaches 170 degrees it starts to run bad and cut off. I have not personally checked the timing chain yet but I have spoken to multiple shops and they believe since it is not throwing any codes that the timing chain probably isn't the culprit. I only paid $650 for the truck with 190,000 miles so I'm trying to stay relatively cheap. I am a lead tech at a GSE shop at PTI Airport in Greensboro so I am capable of working on all types of things gas, Diesel, and electric. At this point I'm stuck with what to do. Any help is greatly appreciated! I figured I'd post on here before I take it to pure diesel in kernersville, North Carolina and pay them to diagnose and fix it. I'm new to this forum and I have never been very good with posting on them so I'm not sure if my signature will show up.

 

[ak diesel driver]

The very first thing to do is install a piece of clear tubing on the return line coming out of the IP. Air is the number one issue seen.
Having said that are you verifying the temp as seen by the PCM or just the dash gauge?
I would also do the OS and CPS tests.

 

[Rockabillyrat]

I agree, check for air in the return line. I'd also put a pressure gauge on the supply side and see if your having and issue there. The oil pressure switch supplies power to the pump. It may be dropping out when it gets warm.

If that checks out I'd look really close at the injection pump wiring. If you have a lab scope check the optical sensor signal at the PCM. Wiggle the harness with the truck at ambient and warmed up and see if it drops out. But being OBD2 it should normally set a code.

Also I like to check all the pressure and temp sensors on the scanner with the truck at ambient temp. Makes it easy to catch ones that off if it's not reading correctly.

 

[Loganshaw_6]

The very first thing to do is install a piece of clear tubing on the return line coming out of the IP. Air is the number one issue seen.
Having said that are you verifying the temp as seen by the PCM or just the dash gauge?
I would also do the OS and CPS tests.

Is the return the fitting pointing straight up out of the pump or the one pointed slightly forwards on an angle? I forgot to add that the truck has a new ops and cos as well. Verified temp from the snap on Solus.

 

[ak diesel driver]

It's the small 1/4" one angled slightly towards the radiator. It's normal for it to have a bubble at the top of the loop but no moving bubbles should be present, even tiny ones. Replace that black tubing with the cheap clear plastic stuff you can get at any hardware store.
Also new parts don't mean good parts, and the wiring/connections are also suspect

 

[Will L.]

Welcome

 

[Wreckinball67]

First of all, I agree with the others. What was wrong with the original ECM? 170° is about the temperature that the ECM goes into a closed loop. Perhaps the ECM is not properly grounded.

 

[Loganshaw_6]

First of all, I agree with the others. What was wrong with the original ECM? 170° is about the temperature that the ECM goes into a closed loop. Perhaps the ECM is not properly grounded.

When I had the truck looked at I was told the truck was losing cam signal they went through the test procedure and diagnosed it to be a bad optical sensor. I have since replaced the injection pump with another pump ac delco but we spoke about getting a new computer just to be sure in the event the old IP back fed the computer. I should also be able to get rid of my EGR since the new used computer does not have one. It still currently does it with both computers.

 

[Loganshaw_6]

It's the small 1/4" one angled slightly towards the radiator. It's normal for it to have a bubble at the top of the loop but no moving bubbles should be present, even tiny ones. Replace that black tubing with the cheap clear plastic stuff you can get at any hardware store.
Also new parts don't mean good parts, and the wiring/connections are also suspect

When the truck shuts off it acts like you turned the key off. It runs fine any other time no misfires no stumbling. Would air bubbles affect it all the time or just past 170 once it's warmed up?

 

[Will L.]

Air bubbles can do both. Most likely you are dealing with an electrical issue, however if you have ANY air in the line which is super common, it will throw off all your settings and adjustments. That is why GM says the very first thing to do is verify no air in system.

The clear line is less than 5 minutes to install and less than $5. It will be step #1 in any diagnostic ls for as long as you own the truck. Afaik, none of us ever remove the clear line except to replace it with another clear line a few years down the road when it can no longer be seen through. When you buy the 12” piece and cut off the piece you need, put the other part in a closed place from uv light and you can use it in a few years when needed.
When I had truck owners as me when I worked in the dealership I had to say” I can’t recommend leaving the clear tube on there all the time, however on my person 6.5 I can show you I always have one on mine...”

Unfortunately having all those parts changed will have made finding the one actual problem difficult.

Something you need to do is treat it as if every part installed is faulty and was installed wrong. Begin by removing all the grounds, cleaning them, and reinstalling them. Engine grounds, and ecm ground. Battery cables as well. Pain in the neck but needed. Meter it out to ensure the grounds are solid afterwards. Then after no air intrusion and grounds are all corrected, then you can go forward.

 

[Loganshaw_6]

Air bubbles can do both. Most likely you are dealing with an electrical issue, however if you have ANY air in the line which is super common, it will throw off all your settings and adjustments. That is why GM says the very first thing to do is verify no air in system.

The clear line is less than 5 minutes to install and less than $5. It will be step #1 in any diagnostic ls for as long as you own the truck. Afaik, none of us ever remove the clear line except to replace it with another clear line a few years down the road when it can no longer be seen through. When you buy the 12” piece and cut off the piece you need, put the other part in a closed place from uv light and you can use it in a few years when needed.
When I had truck owners as me when I worked in the dealership I had to say” I can’t recommend leaving the clear tube on there all the time, however on my person 6.5 I can show you I always have one on mine...”

Unfortunately having all those parts changed will have made finding the one actual problem difficult.

Something you need to do is treat it as if every part installed is faulty and was installed wrong. Begin by removing all the grounds, cleaning them, and reinstalling them. Engine grounds, and ecm ground. Battery cables as well. Pain in the neck but needed. Meter it out to ensure the grounds are solid afterwards. Then after no air intrusion and grounds are all corrected, then you can go forward.

I'm looking at the wiring right now I'll go ahead and put that clear hose on I do notice that there are some spices and black heat shrink with sealant in the wiring harness, not sure what is factory. Does anybody have a good online link to a wiring schematic?

 

[JMJNet]

Just a note, that ACDelco does not make the IP.
Stanadyne is the manufacturer of the IP.
So, an ACDelco reman IP does not necessarily means that it is good.
It depends on who do the reman/rebuild.

Unfortunately, there are a lot of bad reman/rebuild outfit.
I would find an authorized rebuilder and buy from them and I know they are not cheap because of the Quality Control.

 

[Loganshaw_6]

Just a note, that ACDelco does not make the IP.
Stanadyne is the manufacturer of the IP.
So, an ACDelco reman IP does not necessarily means that it is good.
It depends on who do the reman/rebuild.

Unfortunately, there are a lot of bad reman/rebuild outfit.
I would find an authorized rebuilder and buy from them and I know they are not cheap because of the Quality Control.

Correct I agree with that, a lot of it came down to price. I did find an authorized stanadyne dealer in Greensboro that is willing to rebuild the pump $995 out the door with a new PMD.

 

[Will L.]

GM did wire splices like that all over the place. Sorry I don’t have a schematic for ya.

 

[BIGR]

Welcome Loganshaw_6. Looks like you have already got some great advice from these guys.

No question is too tough for them, someone will have an answer. You have come to the right forum, some of the most knowledgeable diesel guys in the World on here.

Good luck on your issues, follow these guys advice and you will get things worked out.

 

[ak diesel driver]

Kinda sounds like a PMD or PMD wiring issue. You do have a resistor in the plug, right? Also try plugging it back in minus the cable right at the IP

 

[Loganshaw_6]

Kinda sounds like a PMD or PMD wiring issue. You do have a resistor in the plug, right? Also try plugging it back in minus the cable right at the IP

Yes it has a #9 resistor

 

[Rockabillyrat]

The best I can do on my phone. You should be able to zoom in on them.

If anyone ever needs wiring diagrams let me know. I have Mitchel at work.

Edit: well I guess you cant zoom in enough to read them. Maybe I can email them to you.

 

[JMJNet]

Is the Lift Pump PUMPING?

 

[WarWagon]

You have the PMD on a heat sink or on the pump? It will overheat and burn out without a heat sink.

The hole in the black wire loom in the left of your picture : are there rubbed through wires in it?

When the truck stalls after warm up: what are the dash lights doing? SES or STS lights come on?

Here is detailed troubleshooting of the PMD that dies in a codeless way. It's buried in the cal resister PDF. https://www.thetruckstop.us/forum/t...-5-db2-5-7l-info-online-from-stanadyne.26581/