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Lost acceleration

Tiny
I_MBOWTIE
  • MEMBER
  • 2008 CHEVROLET EXPRESS
  • 6.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 279,000 MILES
I bought this van used and I put on most of the mileage myself, it has always had this condition so I know that high mileage isn't the problem. When I stomp the accelerator to the floor from a gentle roll as if trying to pass someone, it feels like I'm dragging a boat anchor. Then you can feel it kind of surging up to speed but it takes quite a while to get there. I put plugs and wires on it when I bought it and it generally runs real good. It has never set a MIL or any codes, it just has no get up and go on hard acceleration, seems like this big ole 6.0 should be a screamer. Ever hear of such a thing?
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Tuesday, September 10th, 2019 AT 3:07 PM

15 Replies

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

You might want to double check the spark plug gap which I have included in the diagrams down below. You might also verify that the air filter has been replaced and that the fuel system is clean and working as it should. I have also included in the diagrams down below the factory guides for replacing your vehicle's air filter and cleaning it's fuel system. Please go through these guides and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros
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Thursday, September 12th, 2019 AT 12:20 PM
Tiny
I_MBOWTIE
  • MEMBER
  • 39 POSTS
I did find bad spark plugs and replaced them and a new set of wires. Pulled the fuel tank module and the tank is shiney clean inside, no debris. It runs and idles real good and smooth, but it still has a slow acceleration response. No engine codes. I also cleaned the throttle body. I'm just attempting to get away without having to pay a high cost of a shop diagnosis.
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Saturday, September 14th, 2019 AT 5:11 PM
Tiny
JIS001
  • MECHANIC
  • 3,408 POSTS
Hello and welcome to 2CarPros. Just wanted to jump in. So you stated earlier there are no current or pending codes posted correct? Give us these readings when you have time. Warm up the engine. Once warmed up and in close loop, turn all accessories off. Look at the mass air flow reading and give us the value at idle. Next drive the vehicle to 40 MPH cruising. Hit the accelerator pedal WOT and give us the reading of the mass air flow sensor and how high it jumps up too. The readings will give us an idea as to how the mass air flow is doing.

Next hook up a fuel pressure gauge and tape it to the windshield. What is the pressure at idle and what is the pressure when you feel the lag? Lastly, can you go to mode 6 data and give us the catalytic converter test results to check for a partially plugged catalytic converter? Also how many miles those the wife's van have compared to your van? Let us know please.
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Wednesday, September 18th, 2019 AT 12:51 AM
Tiny
I_MBOWTIE
  • MEMBER
  • 39 POSTS
First I'd like to thank you for showing an interest in my issue. The previous agent made me feel he wasn't really interested in helping me as he kept asking questions that I had already answered in my initial email. I will try to gather this data and get back to you.
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Wednesday, September 18th, 2019 AT 3:35 PM
Tiny
JIS001
  • MECHANIC
  • 3,408 POSTS
Hello and welcome back. Thank you for responding back. When you get the mass air flow readings can you give us the values in grams per second please? I forgot to mention that in my previous post so that there is no miscommunication.
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Thursday, September 19th, 2019 AT 1:07 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,969 POSTS
If I could jump in as well. I would check the catalytic converter and replace the MAF with a new unit. if the catalytic converter is okay here are two guides to help us find out:

https://www.2carpros.com/articles/engine-has-low-power-output

and

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Please run down these guides and report back.
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Monday, September 23rd, 2019 AT 4:20 PM
Tiny
I_MBOWTIE
  • MEMBER
  • 39 POSTS
Sorry for taking so long to get back, had some emergencies. Here are the MAF sensor readings,
idle-6.45 g/s
Acc. WOT-240.71 g/s
18.65 g/s @ 40 mph.
I worked in Muffler shops most of my early working life so I know the Catalytic converters are good, no hesitation or power lose during any other situation other than under hard acceleration. It runs down the highway very good and getting 13.4 MPG Those were the first thing I checked. There is great flow out of the tail pipe and no excessive heat from the converters. I can't do the fuel pressure reading because my gauge has a short hose on it and the test port is in the middle of the engine since it is a van.
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Sunday, October 13th, 2019 AT 7:57 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,002 POSTS
Welcome back, No need to apologize, life sometimes tosses a curve ball. Being this is a van, do you know the rear gear ratio? Do you feel the transmission drop out of lock-up and at least one gear more at WOT? Does the rpm jump and then it picks up speed like the transmission is slipping, or does it just bog down and slowly climb? What does it do if you shift it up manually instead of leaving it in drive?
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Wednesday, October 16th, 2019 AT 4:35 PM
Tiny
I_MBOWTIE
  • MEMBER
  • 39 POSTS
It's 3.73 gear ratio, yes I feel it drop out of lockup and at least 1 gear. It feels like I'm dragging a boat anchor it picks up speed and eventually hits top speed but very slowly. My wife has the identical van and her's hauls ass on hard acceleration, her's has 178,000 miles.
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Thursday, October 17th, 2019 AT 4:11 AM
Tiny
I_MBOWTIE
  • MEMBER
  • 39 POSTS
It just seems like this new gen. 6.O should have more ponies than it feels.
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Thursday, October 17th, 2019 AT 4:13 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,002 POSTS
Reading through everything I would get the fuel pressure tested and check that you are getting enough fuel. The MAF numbers look okay. So it's unlikely to be something like a plugged exhaust and the transmission doesn't seem to be the issue. Mileage seems a bit low but you're driving a brick with an engine that isn't known for mileage.
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Thursday, October 17th, 2019 AT 7:37 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,969 POSTS
Try to check the catalytic converter. here is a guide:

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Please run down this guide and report back.
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Saturday, October 19th, 2019 AT 10:45 AM
Tiny
I_MBOWTIE
  • MEMBER
  • 39 POSTS
Yes, I already did this in a previous reply.
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Sunday, October 20th, 2019 AT 5:43 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,969 POSTS
I see he MAF reading and they can be a little low causing the PCM to think the amount of air entering the engine is less than it really is in turn reducing fuel and power. I would try a new MAF sensor which if you have not replaced with that many miles I would do it. This sensor is a normal service replacement item. Also check the air filter. Check out the diagrams (below). Please let us know what happens.
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Sunday, October 20th, 2019 AT 11:51 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,002 POSTS
What does the TPS voltage look like?
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Sunday, October 20th, 2019 AT 3:28 PM

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