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I have a 2002 GMC Sierra 3500 duallywith a, With a 6.6

I have a 2002 GMC...
I have a 2002 GMC Sierra 3500 dually*****with a
JA: Besides this, what condition is the car in?
Customer: With a 6.6 diesel and Allison tranny. When I get on it and it reaches a shift point the rpm's will level off she throws a lot of black smoke and won't shift up. If I let off the throttle a bit, it will shift and accelerate until the next shift point then act the same way. I have two codes, first one is low fuel pressure under power surge. The second is a class two communication error. What do you think.
JA: Are you fixing your Sierra yourself? What have you tried so far?
Customer: Yes I'll be fixing it myself, I've tried nothing yet I haven't had any time and won't until next week.
JA: Anything else you want the mechanic to know before I connect you?
Customer: Not that I can think of. Thank you.
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Answered in 3 hours by:
9/7/2017
Marvin the Mechanic
Marvin the Mechanic, ASE Certified Technician
Category: GMC
Satisfied Customers: 88
Experience: Mechanic for 36 years
Verified

With what you describe. Have you changed the fuel filter lately? with the low fuel code the filter might be starting to get restricted.

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Customer reply replied 2 months ago
I have recently changed the filter, that was my first thought. I misspoke on the code. It was not low pressure on power surge, I should have said power enrichment.

Another thing that might cause this would be an air hose off from the air cleaner to the engine

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Customer reply replied 2 months ago
That I have not checked. I will in the morning and will let you know tomorrow how I made out. Thank you sir.

I will check back in the morning. Do you hear a whistle when you accelerate?

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Customer reply replied 2 months ago
No noises or bad hoses that I can find.

Do you have a scan tool to command the fuel pressure high? See what the fuel pressure will go up to. Also see what the balance rates are on the injectors.

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Customer reply replied 2 months ago
The balance rates are;
1. -1.7
2. 1.3
3. 2.5
4. 1.1
5. 1.9
6. -1.0
7. -1.7
8. .3
As far as fuel pressure I could run it up to 100% but the higher I went the engine would make an increased noise and run a little rough then recover.

The engine will make noise when you increase the pressure. Does the actual vs desired go up together?

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Customer reply replied 2 months ago
it did?
Customer reply replied 2 months ago
I'm going to pop a new fuel filter in again. Perhaps I got some dirty fuel or a bad filter. At least I'll feel more confident about the filter. Do you think the U1000 class two communication error has anything to do with it? Like maybe it's not allowing the fuel to increase because it's at a shift point and not shifting? It will shift and take off if I feather the pedal a little, but only until the next shift point.

Let me know about the fuel filter.

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How did the fuel filter change go? Did the problem get corrected with the fuel filter?

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Customer reply replied 2 months ago
I'm doing the fuel filter this afternoon, I'll keep you posted and thank you for all your help I appreciate it very much.
Customer reply replied 2 months ago
Changing the filter did nothing however cleaning every communication connection I could find did cure it. Thank you very much for your assistance.

Please take a moment to rate my service so I can get credit for my time, the question remains open for follow up even after doing so, all you need to do is return to this question if need be.

Thank you again.

Marvin the Mechanic
Marvin the Mechanic, ASE Certified Technician
Category: GMC
Satisfied Customers: 88
Experience: Mechanic for 36 years
Verified
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