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rpmdiag, Tech and Instructor
Category: GMC
Satisfied Customers: 8144
Experience:  Since 1975
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Have a 2005 gmc 7500 with the Isuzu 7.8 l in it. I step on

Customer Question

have a 2005 gmc 7500 with the Isuzu 7.8 l in it. I step on the pedal, the truck revs but basically goes nowhere, and sometimes itll let me do 30mph......took it to a mechanics shop they cant scan it, took it to a gmc dealership, the read it (pulled a few codes one had to do with fuel/low voltage at the rail) dealer ship said they cant/ wont clear the code......I need this truck back asap......not sure where to start
Submitted: 1 year ago.
Category: GMC
Expert:  rpmdiag replied 1 year ago.

Hi, I’m Ron and I can help you.
I have been in the auto repair business with my own shops since 1975 and also teach
automotive repair. I am confident we can resolve your problem together. Please
understand that I don't know your skill level. In most cases when you have a problem
with the way the vehicle performs, specialized tooling is required to acquire computer
data/information or engine testing results. We didn’t build these complicated vehicles; we
just diagnose and fix them. Also understand that I can't see, smell, hear, or touch the
vehicle either, so it may take a few replies to get to satisfactory results. I am also going to
direct you with the fastest, easiest and most common things to check first. Please be
patient and permit me to do what I do best.
I also try to give all of the information you may need, expecting a “positive rating” in
return. I will also continue assisting you after you have rated me, if necessary. If there
is any reason I cannot get a positive rating, please let me know why “in advance”, so I
can go another direction for you. I am sorry you’re having this problem; I’ll help you
through it.

It sounds like it's in limp mode and they need to find out why by use of the scan tool.It doesn't sound like they did much for you at the dealer, so let's try this first. See attachment,we need to relearn the computer first, and this can actually fix it too if we're lucky.

Thanks, Ron