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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1685
Experience:  GM Grand Master Technician 2007. 14 year experience.
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GMC serria: i have a 1996 6.5 turbo diesel also, it accelerates

Customer Question

i have a 1996 6.5 turbo diesel also, it accelerates fine but when you get to speed like 55 mph and let off to maintain that speed it's like you took your foot off the accelerator
Submitted: 1 year ago.
Category: GMC
Expert:  Toolhut replied 1 year ago.
Hi, My Name is***** have over 20 years experience repairing vehicles. I am a ASE Certified Master Auto Technician. I am confident we can resolve your problem together.Please remember I don't know your skill level. I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies to get to a satisfactory resoloution. Try your best to respond with good detail so I can do the same.Have you done any testing? I am suspicious you have a fuel delivery problem. Plugged filter or mechanical fuel pump. Do you have any test equipment?
Customer: replied 1 year ago.
no test equipment but have replaced filter
Expert:  Toolhut replied 1 year ago.
The next thing I would check is fuel pressure and volume from the mechanical pump. There is a possibility that you have a Injector pump module that is causing problems. But You need to rule out the fuel pump first. There is an upgrade to remount the module if it is still attached to your injector pump to out of the engine so it cools better. Do you know if there have been any upgrades done to this engine?
Customer: replied 1 year ago.
yes i have already replaced PDM on a cooler
Expert:  Toolhut replied 1 year ago.
I do not know where to tell you to go so I am going to opt out and see if a different professional has any suggestions.
Expert:  JFN1 replied 1 year ago.
Is the check engine light on, or do you know/have you checked for trouble codes?
Customer: replied 1 year ago.
the check engine light is not on and i have not checked any codes
Expert:  JFN1 replied 1 year ago.
I'm trying to wrap my mind around your symptom. When you say it's like you took your foot off the accelerator when you are trying to drive at steady speeds, what exactly is going on? Does the engine go to idle?
Customer: replied 1 year ago.
I don't take my foot off I just ease off to allow the truck to slow a bit it it fells like I take my foot off compleatly
Customer: replied 1 year ago.
You can see tack drop in rpm
Expert:  JFN1 replied 1 year ago.
Do you think it's an engine issue, or is it a transmission issue?
Customer: replied 1 year ago.
I'm thinking engine but could be wrong
Customer: replied 1 year ago.
Today I put transmission in neutral and pressed the throttle slightly and engine reved to 4000 rpm , as I drive it to town later I noticed if I left foot on throttle slightly it would increase in speed and blow out black smoke so seems engine is running away to me
Customer: replied 1 year ago.
Did you give up too ?

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