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97 gmc: diesel automatic..automatic 4+4 dually crew-cab..acceleration…

Customer Question
I have a 97 GMC...
I have a 97 GMC 6.5 turbo diesel automatic 4+4 dually crew-cab. My problem is a sudden acceleration every now and then. It doesn't seem to matter what speed I am going. at times I will just be moving slowly in traffic when the engine gets a burst of extra power and will lurch ahead without any warning. at times on the highway it will kinda "shimmy" for a second with an extra burst of really fast , quik acceleration. it goes away as fast as it comes. Its almost as though its getting an extra flush of fuel without pressing the fuel pedal any harder. The engine light was on for a short time ( couple days) then went off but my truck continues to overcompensate about 3 to 5 times in a 2 hour trip. It only seems to do it when its warmed up and it hasnt overheated or gotten too warm.I am totally new to diesel, thank you for your help!
Submitted: 8 years ago.Category: GM
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Answered in 2 hours by:
6/15/2010
GM Mechanic: GM Tech (Cam), GMC Mechanic replied 8 years ago
GM Tech (Cam)
GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 30,416
Experience: GM Grand Master Technician 2007. 14 years experience.
Verified

Greetings and Welcome to Just answer.

Are there any warning lights on in the dash?

 

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Customer reply replied 8 years ago

Very good question! The engine light just popped back on this morning! Also, I would like to know where the throttle posistioning sensor is located. I purchased this sensor in hopes it would solve my acceleration problem.

GM Mechanic: GM Tech (Cam), GMC Mechanic replied 8 years ago
Well there is the accelerator position sensor on the throttle pedal, and that is it.
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Customer reply replied 8 years ago
Will this solve my problem? The throttle postng sensor was just a wild guess on my part, I would like to know what may cause the sudden acceleration AND where to begin the process of elimination, Thank you
GM Mechanic: GM Tech (Cam), GMC Mechanic replied 8 years ago

There is a small chance it will, but the odds are against it. I really think it is in the injection pump itself.

For now I would get the code from the system. Most part stores can get this code for you and usually for free.

 

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Customer reply replied 8 years ago
Please? What do I do with the code once I get it? Are you suggesting I replace the whole injection pump itself or should I make sure the fuel lift pump or even the oil pressure switch FOR the(relay or electric) fuel lift pump are in working order first? I am also curious about the VSSB module, vehicle speed sensor buffer and the Phaser-duel idler gear drive as both of these are linked with the timing as well, if system failure in either of these could cause the periodic acceleration ?
GM Mechanic: GM Tech (Cam), GMC Mechanic replied 8 years ago

Reply here with the code.

The VSSB should not be linked to the throttle, but other is and is internal to the injection pump. If I may, almost every one of these 6.5L diesel engines will need a new injection pump at one point. There was a flaw in the Design. GM even had a special policy for them, but that has now expired.

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Customer reply replied 8 years ago
Can you please tell me where or how to obtain the code for this system? The auto parts place we have here is adamant that I provide the code before they can look up the part.
GM Mechanic: GM Tech (Cam), GMC Mechanic replied 8 years ago

What code are they looking for, the engine code?

 

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Customer reply replied 8 years ago

I believe he was asking for some type of code that would be located on the injection pump itself . Oh boy, perhaps he meant the code for the system.

GM Mechanic: GM Tech (Cam), GMC Mechanic replied 8 years ago
There is a code on the pump, the pain is getting at it. This code is on the back of the pump. If you take the upper plenum off you can use a mirror to see the code on the back.
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