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Diesel running rough when outside temperatures change to cold?

Tiny
TERRALL
  • MEMBER
  • 1996 CHEVROLET 2500
  • 6.5L
  • V8
  • 4WD
  • AUTOMATIC
  • 193,000 MILES
Hello. I have the truck listed above K2500 4x4 6.5 turbo diesel. The truck runs perfectly when temperatures outside are 70 degrees and above. But as soon as it's below that the worse it runs and the colder it is even worse it runs. But as you drive it, it starts running smoother and then to normal. It also had a hard starting issue when it's cold out. But again, once it is 70 degrees it will fire no problem. Once it starts it idles perfectly and warms right up to temperature. I have put new glow plugs in it. Fuel pump and pressure is good throughout. Two new PMD with resistors. I just don't know why it runs perfectly in the summer and horrible in the winter. Thanks
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Saturday, December 9th, 2023 AT 6:07 PM

9 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,959 POSTS
I have seen the engine coolant temperature sensor go out and cause this issue, but can I ask if you have run the codes?

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Here is information I found on the PDM:

The PMD in these engines is known to have issues, primarily due to its original location on the injection pump, where it is exposed to significant heat. This heat exposure can lead to failure of the PMD, resulting in engine stalling, hard starting, or other performance issues. As a remedy, many owners and mechanics relocate the PMD to a cooler area in the engine bay to improve its reliability and lifespan.

Here is the location of the engine coolant temperature sensor in case you what to swap it out. Check out the images (below). Let us know how it goes
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Monday, December 11th, 2023 AT 11:13 AM
Tiny
TERRALL
  • MEMBER
  • 5 POSTS
Thanks Ken. I will replace that sensor. I thought I did when I put my turbo gauge on. But I may not have. The computer is not throwing any codes. I did relocate the PMD to a cool place. I thought maybe the injection pump may be going bad. Bud it just doesn't make sense if it runs excellent in the warm weather. Sadly, where I live no one seems to work on 6.5. But one mechanic thought it may need a new injection pump but wasn't sure. Plus, when I open the fuel line it pours right out nicely. Again, thanks for all your help. I will replace the sensor and get back to you.
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Tuesday, December 12th, 2023 AT 9:34 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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You are welcome please let me know how it goes. The sensor should fix the problem.
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Thursday, December 14th, 2023 AT 10:53 AM
Tiny
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  • MEMBER
  • 5 POSTS
I put a new sensor on it and unfortunately it still runs the same.
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Friday, January 5th, 2024 AT 6:20 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,959 POSTS
I am sorry to hear that, are there any other trouble codes? Also did you change out the fuel filter/water separators? This video will show you how:

https://youtu.be/lEbTuBAULD4?si=aa8qNCW-VqaMJuxE

Please go over this guide and get back to us.
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Sunday, January 7th, 2024 AT 10:03 AM
Tiny
TERRALL
  • MEMBER
  • 5 POSTS
Yes, I have replaced the fuel filter. Just seems so weird that it's 40 degrees and it idles perfectly but the acceleration is either all or nothing. Like somewhere in the middle, it's missing until warmed up. Then you can slowly feel that miss start getting better. But if it is 80degrees it acts like nothing is even wrong with it. With it being a 1996, is there a fuel heater in these trucks that warm up the fuel before the injection pump? Just wondering if that would make sense in only the cold. I did take it in and the guy wasn't for sure but said it was probably the injection pump. But the injection pump pours good fuel out of it and wouldn't make sense that it would get better the longer you drive it. But if it only idols it will still run crappy. It has to be driving around on the hwy for it to start running correctly. I have went hunting and driving it slowly does fine but as soon as I get on the hwy it will have that miss come on and then 20 minutes later it runs perfectly. Thanks again for your help Ken.
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Sunday, January 7th, 2024 AT 1:33 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,959 POSTS
Yep, it sounds like the fuel injection pump is going bad, at least we went over everything else first. Here are the instructions on how to change it out. Check out the images (below). Let us know what you find.
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Monday, January 8th, 2024 AT 9:02 AM
Tiny
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Should I change the timing chain while I'm in there and put in new fuel injectors in it? Is this a big job? How many hours should I expect? Thanks
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Monday, January 8th, 2024 AT 10:31 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,959 POSTS
If you want to do a timing chain please start new thread we only handle one problem per question. I would install new fuel injectors while you are there, here is how. Check out the images (below). Let us know what you find.
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Tuesday, January 9th, 2024 AT 9:50 AM

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