2006 c4500 duramax help!

Chain ChaTTer
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Chain ChaTTer

Hello!… I'm hoping there are some mechanics out there that could give me some advice on what's going on with my truck… I was returning from the nursery on Monday and the truck lost power and won't go above 35 now ...2000rpms-ish

I pumped it to the closest mechanics who are now telling me that I need a new $8000 transmission, but I just simply refuse to believe that this is the case

The truck didn't make any screeching loud noise or lose the ability to drive, but rather felt like it was restricted in someway...went into limpmode

 After doing some research online I am seeing a lot of other c4500 Kodiak  owners of  05-06-07 model saying the exact same thing although I can never follow the thread enough to get to the point of the solution


 Hoping there is somebody out there with some sort of experience with this ...a solenoid perhaps? Filters?

There are times I can't start the truck after leaving a job site and I have to lift the hood and manually pump the fuel primer until firm and then it will start

The truck has 100,000 miles on it and runs beautifully and if I'm wrong, I'm wrong but I just refuse  believe that a new transmission is what's needed

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PNWMXer
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PNWMXer 4/14/2025 5:06am
4/14/2025 5:06am

Any codes?

Will it rev in neutral /park?

Any smoke, strange engine sounds?

Does it have a lift pump (in addition to the HPCR pump)? If so, the need to occasionally pump the primer could point to this being bad (can’t pump enough fuel from the tank to the injection pump to make power).

You need to isolate whether it’s an engine problem, transmission problem, or both.

I would get it to a good independent diesel shop (NOT a dealership). Pay a few $$$ for a diagnostic. Go from there.
 

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AJ565
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AJ565 4/14/2025 5:54am
4/14/2025 5:54am

We had issues with people not changing the red spin on filter often enough (supposed to be every 7500 miles) and it would cause the issue you're describing. It was less common, but the fuel filter would also cause it (supposed to be changed every 14,000 miles). Both are a cheap try to see if it takes care of the issue. 

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Chain ChaTTer
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Chain ChaTTer 4/14/2025 7:41am
4/14/2025 7:41am
PNWMXer wrote:
Any codes?Will it rev in neutral /park?Any smoke, strange engine sounds?Does it have a lift pump (in addition to the HPCR pump)? If so, the need...

Any codes?

Will it rev in neutral /park?

Any smoke, strange engine sounds?

Does it have a lift pump (in addition to the HPCR pump)? If so, the need to occasionally pump the primer could point to this being bad (can’t pump enough fuel from the tank to the injection pump to make power).

You need to isolate whether it’s an engine problem, transmission problem, or both.

I would get it to a good independent diesel shop (NOT a dealership). Pay a few $$$ for a diagnostic. Go from there.
 

So the motor runs perfectly .....no crazy noises nothing.

On a few occasions now I've been on a job and I go to leave and the truck turns over fine but won't fire

Another tradesman showed me to pump the fuel primer manually..I did/do that and it fires straight away?

Would that have anything to do with it?

Also I found this...this looks like a pickup but wondered if my truck has this? I know it has an Allison but I don't know if it's 5 speed.

https://www.youtube.com/watch?v=9yN5FzWwnRU&pp=ygUJYzU1MDAgdGNt

I really appreciate the help

The Shop

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Chain ChaTTer
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Chain ChaTTer 4/14/2025 7:45am
4/14/2025 7:45am
AJ565 wrote:
We had issues with people not changing the red spin on filter often enough (supposed to be every 7500 miles) and it would cause the issue...

We had issues with people not changing the red spin on filter often enough (supposed to be every 7500 miles) and it would cause the issue you're describing. It was less common, but the fuel filter would also cause it (supposed to be changed every 14,000 miles). Both are a cheap try to see if it takes care of the issue. 

 Can I access these under the hood?

I have a broken arm currently so can't get underneath the truck but could look from top

Can I get these from Napa?

I'm sorry I'm desperate and can't be without this truck

ParkingLotWheelies 4/14/2025 10:53am
4/14/2025 10:53am Edited Date/Time 4/14/2025 10:59am
PNWMXer wrote:
Any codes?Will it rev in neutral /park?Any smoke, strange engine sounds?Does it have a lift pump (in addition to the HPCR pump)? If so, the need...

Any codes?

Will it rev in neutral /park?

Any smoke, strange engine sounds?

Does it have a lift pump (in addition to the HPCR pump)? If so, the need to occasionally pump the primer could point to this being bad (can’t pump enough fuel from the tank to the injection pump to make power).

You need to isolate whether it’s an engine problem, transmission problem, or both.

I would get it to a good independent diesel shop (NOT a dealership). Pay a few $$$ for a diagnostic. Go from there.
 

Chain ChaTTer wrote:
So the motor runs perfectly .....no crazy noises nothing.On a few occasions now I've been on a job and I go to leave and the truck...

So the motor runs perfectly .....no crazy noises nothing.

On a few occasions now I've been on a job and I go to leave and the truck turns over fine but won't fire

Another tradesman showed me to pump the fuel primer manually..I did/do that and it fires straight away?

Would that have anything to do with it?

Also I found this...this looks like a pickup but wondered if my truck has this? I know it has an Allison but I don't know if it's 5 speed.

https://www.youtube.com/watch?v=9yN5FzWwnRU&pp=ygUJYzU1MDAgdGNt

I really appreciate the help

This sounds a lot like the symptoms of a bad filter head. A new one is <$100 and can be changed very easy, or they sell rebuild kits for really cheap. Do you have a lift pump? It would have been installed aftermarket, and you would have fuel filters on the pump; i.e. you would know if you had one. 

ETA: I lied, the filter head is more than $100, but not much more.

ParkingLotWheelies 4/14/2025 10:55am
4/14/2025 10:55am
AJ565 wrote:
We had issues with people not changing the red spin on filter often enough (supposed to be every 7500 miles) and it would cause the issue...

We had issues with people not changing the red spin on filter often enough (supposed to be every 7500 miles) and it would cause the issue you're describing. It was less common, but the fuel filter would also cause it (supposed to be changed every 14,000 miles). Both are a cheap try to see if it takes care of the issue. 

Chain ChaTTer wrote:
 Can I access these under the hood?I have a broken arm currently so can't get underneath the truck but could look from topCan I get these...

 Can I access these under the hood?

I have a broken arm currently so can't get underneath the truck but could look from top

Can I get these from Napa?

I'm sorry I'm desperate and can't be without this truck

Red spin on filter is underneath, although I don't think it would cause the issues you're having. The fuel filter (at least on my '15 Duramax) is located inside of the front passenger wheel well. If you haven't replaced it recently, it could be another easy thing to replace.

Cool_Hand_Luke 4/14/2025 1:30pm
4/14/2025 1:30pm
PNWMXer wrote:
Any codes?Will it rev in neutral /park?Any smoke, strange engine sounds?Does it have a lift pump (in addition to the HPCR pump)? If so, the need...

Any codes?

Will it rev in neutral /park?

Any smoke, strange engine sounds?

Does it have a lift pump (in addition to the HPCR pump)? If so, the need to occasionally pump the primer could point to this being bad (can’t pump enough fuel from the tank to the injection pump to make power).

You need to isolate whether it’s an engine problem, transmission problem, or both.

I would get it to a good independent diesel shop (NOT a dealership). Pay a few $$$ for a diagnostic. Go from there.
 

Chain ChaTTer wrote:
So the motor runs perfectly .....no crazy noises nothing.On a few occasions now I've been on a job and I go to leave and the truck...

So the motor runs perfectly .....no crazy noises nothing.

On a few occasions now I've been on a job and I go to leave and the truck turns over fine but won't fire

Another tradesman showed me to pump the fuel primer manually..I did/do that and it fires straight away?

Would that have anything to do with it?

Also I found this...this looks like a pickup but wondered if my truck has this? I know it has an Allison but I don't know if it's 5 speed.

https://www.youtube.com/watch?v=9yN5FzWwnRU&pp=ygUJYzU1MDAgdGNt

I really appreciate the help

ParkingLotWheelies wrote:
This sounds a lot like the symptoms of a bad filter head. A new one is <$100 and can be changed very easy, or they sell...

This sounds a lot like the symptoms of a bad filter head. A new one is <$100 and can be changed very easy, or they sell rebuild kits for really cheap. Do you have a lift pump? It would have been installed aftermarket, and you would have fuel filters on the pump; i.e. you would know if you had one. 

ETA: I lied, the filter head is more than $100, but not much more.

I concur. He said if he primed it it would start......so.

1

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