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ON ACCELERATION IT IS SLUGGISH BUT THE CONVERTERS HAVE BEEN…

Customer Question
ON ACCELERATION IT IS...

ON ACCELERATION IT IS SLUGGISH BUT THE CONVERTERS HAVE BEEN TAKEN OFF AND IT HAS A RECENT TUNE UP AND PUT ON A COMPUTER. IT ALSO HAS SLIGHT FISH BITE WHEN LUGGING, OR GOING SLOW UP A HILL LIKE A MISS. IT ALSO DON'T GET GOOD MILAGE, THIS IS THE THIRD ONE I HAVE HAD AND THEY BOTH GOT AROUND 13 TO 14 MPG THIS ONE GETS 11.2 AT BEST

Mechanic's Assistant: When did you last clean or replace your air filter? And are the oxygen sensors in good working order?

A WEEK A GO AND OLD WAS NOT TO BAD

Mechanic's Assistant: What is the model/year of your GMC?

07

Mechanic's Assistant: Are you fixing your vehicle yourself? What have you tried so far?

I HAVE HAD A GM TEC THAT HAS STARTED HIS OWN SHOP WORK ON IT AND HE SEEMS TO THINK IT MIGHT BE CARBON BUILD UP IN IT SOME WHERE BE HE IS NOT SURE

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

I THINK THAT IS ALL, I JUST WANT THE TRUCK TO RUN WHEN I STEP ON THE GAS, AS IT IS NOW IT'S LIKE DRIVING A PICK UP WITH A 6 CYLINDER, IT TAKES A WHILE TO GET THE SPEED UP

Submitted: 4 months ago.Category: GMC
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Answered in 38 minutes by:
3/15/2018
GMC Mechanic: Gm Tech (Cam), GMC Mechanic replied 4 months ago
Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 30,403
Experience: GM Grand Master Technician 2007. 14 year experience.
Verified

Hello there, I am Cam.

I am Licensed technician at a GM dealership with more than 16 years experience. 
Like you, I am a user of this website and as such, any billing questions should be sent to customer service.

I ask that you please provide details and communicate with me so we can make your experience here worth 5 stars! I am around most days but not every minute of every day. If you reply while I am offline, I will respond when I am next online. 

I am reviewing your request and will post in a moment.

What model is your GMC?

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Customer reply replied 4 months ago
07
Customer reply replied 4 months ago
07
GMC Mechanic: Gm Tech (Cam), GMC Mechanic replied 4 months ago

The first thing I would look into is fuel. You have ruled out exhaust so lets see if the fuel system is keeping up. Spec is 55-62 psi and even climbing the hills it should be in that range. I suspect it is dropping below that. Testing in the bay will not give you the accurate picture, you need to drive with the gauge on and watch the pressure. I tape it to the windshield to view the pressure.

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Customer reply replied 4 months ago
we did put the guage on the fuel rail and it set on 60 psi when climbing a hill or running down the road it didn't make a difference to the pressure.
GMC Mechanic: Gm Tech (Cam), GMC Mechanic replied 4 months ago

Did the tune up include plug wires?

I am not sure about carbon, the way you describe it sounds like a plug wire is causing issues. I would have your tech see which cylinder gives the misfire when it happens and go from there.
After that I would look to a weak crank position sensor.

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Customer reply replied 4 months ago
New wires and plugs and computer says no miss fires
GMC Mechanic: Gm Tech (Cam), GMC Mechanic replied 4 months ago

Is the scanner you are using sensitive enough to pick up one or 2 misfires? IF your using a GM tech 2, I would be using the misfire graphic in the special functions. It will pick this up.

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Customer reply replied 4 months ago
I will find out
GMC Mechanic: Gm Tech (Cam), GMC Mechanic replied 4 months ago

Ok, perfect. With new wires and plugs, I am wondering about a coil pack as well, but I don't want to suggest replacing all/any until we know which one to go after.

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