6.0 flat spot

031500hd · May 5, 2003

Has anyone figured out the lack of power in the '03 1500 HD Crew cab yet?

At full throttle it kicks down and it feels like it wants to go but there is the feeling that the timing isn't advancing or the air fuel mixture is off. I took it to the dealership and the head mechanic and I went for a ride, he felt it too, its as if there is something holding the truck back from its power potential... any coments or suggestions? "PLEASE" :werd:

Charlie in TX · May 5, 2003

No, I have not experienced what you discribe. When I put my foot in it, it goes.

One question, do you have the 3.73 or 4.10 rear end? The reason I ask is I test drove 5 1500hds with the 3.73. I thought it felt ok. I ordered one with the 3.73. I later test drove a 2500hd CC (only comes with 4.10) and bought it that day. The motor came to life with the 4.10.

I have put 9,000 miles in the last 4 month and I couldn't be happier.

031500hd · May 6, 2003

Hi Charlie,

I do have a 3:73 but I don't believe thats the problem.

When it kicks down the engine RPMs jump to 3500-4500,

it just seem as if the throttle body or the timming isn't keeping up with the instant demand I expected, it revs but goes no where! On the freeway when I nail it sometimes takes a couple of hard accelerator pumps to get it to kick down but when it does it goes!

I had an '02 Denali with the 6.0 and 3:73 gears.. now I know the engines are tuned differently and there is a weight difference but the vehicles engine responded as I expected. I had many cars and trucks infact it's a hobby of mine to work and tinker on them, heck.. my garage looks like an auto shop.

There is definatly something wrong. I hope someone has had the same expierience and may have an answer for me.

dcmargush · July 25, 2007

<font color='#000000'>Hi Charlie,
I do have a 3:73 but I don't believe thats the problem.

When it kicks down the engine RPMs jump to 3500-4500,

it just seem as if the throttle body or the timming isn't keeping up with the instant demand I expected, it revs but goes no where! On the freeway when I nail it sometimes takes a couple of hard accelerator pumps to get it to kick down but when it does it goes!

I had an '02 Denali with the 6.0 and 3:73 gears.. now I know the engines are tuned differently and there is a weight difference but the vehicles engine responded as I expected. I had many cars and trucks infact it's a hobby of mine to work and tinker on them, heck.. my garage looks like an auto shop.

There is definatly something wrong. I hope someone has had the same expierience and may have an answer for me.</font>

I am kindof experiencing a similar problem. Mine is a little worse. In addition to that "lack of power response feeling - that use to be there", I also have a studder at highway speeds, only under load between 1500-2000 RPM. I have worried it was a torque converter going bad (replaced 2 years ago w/ a faile 4l80e), thought fuel pump/filter (replaced last year), but now I actually experienced a studder when I first started it. I started wondering about timming, in the old days I would say the vacum advance was not keeping up to speed. I don't know what determines the timming now adays with the individual coils. I had a very similar experience with my 84 w/HEI coil dist that I had to rebuild.

the pain is that it only happens under load, and I can't hear it back firing out the intake etc cause I am @ 50-60 mph. And the darn thing doesn't throw a code, at least not a visible code to set of the message center.

Ideas? i will also inquire in the Ask the GM tech.

cbxeric · July 29, 2007

just an idea but maybe the electronic throttle is not functioning properly. I don't have that on my truck so I'm not sure how it works.

Good luck.

dalep · July 30, 2007

I also have a problem when towing my 5th wheel with my 03 1500 HD with 6.0 litre 3:73 gears . When i have a headwind it does not perform at all and i have a hard getting the transmission to lock up in drive . Today i could not get 60 miles per hour out of it. I have a magnaflow cat back exaust on it .There are no engine codes showing .It just does not have the power that i think it should.

anealysr · August 25, 2007

I have the same problem at time it's worse than others. Mine flattens out at 4000 rpm in 1st gear then really struggles to make it to the shift to second. When she does she flies I have no codes or misfire either. Any help would be great, I have reset the computer by pulling the battery and no help on relearn.

mhraracing · August 25, 2007

Could it be the dreaded TM ?? - The computer pulling out all kinds of timing to ensure there is no damage to your driveline ?

sparks244 · September 9, 2007

Could it be the dreaded TM ?? - The computer pulling out all kinds of timing to ensure there is no damage to your driveline ?

It could very well be the TM control. I have looked up a full PCM read on a 04 and the TM kicks in due to several conditions (load, Throttle Position, Torque output).

fmjhp594 · April 29, 2008

I had the same issues when pulling a trailer with my 2500hd. Now I do realize I am lifted and running 35" tires. I had a 4.10 rear end that I re-geared to 4.88. Problem solved and my gas mileage when up....

Mudddawg · May 19, 2008

I had the same issues when pulling a trailer with my 2500hd. Now I do realize I am lifted and running 35" tires. I had a 4.10 rear end that I re-geared to 4.88. Problem solved and my gas mileage when up....

Not meaning ti hijak here but how was the power increase and throttle response after the gear swap. I have the same setup only with 4.10 gears and was thinking about the 4.88's.

desrtrat · May 21, 2008

had the same with my 03 SS. would bog about 2500 rpm in second gear. got a good street tune, and cleared it up, no more problems...

slimjim2525 · May 21, 2008

It sounds like the TM. Maybe you need a tune?

jdlmodelt · May 29, 2008

It sounds like the TM. Maybe you need a tune?

Just what exactly do you mean by "you need a tune?"

My 99 6.0l extended cab 2500 4x4 seems weaker than it should be as well, but it is all STOCK, other than a larger 4 inch freeflowing exhaust system with a freer flowing muffler.

James

BigJayDogg3 · May 29, 2008

It sounds like the TM. Maybe you need a tune?

Just what exactly do you mean by "you need a tune?"

My 99 6.0l extended cab 2500 4x4 seems weaker than it should be as well, but it is all STOCK, other than a larger 4 inch freeflowing exhaust system with a freer flowing muffler.

James

A tune is basically a program that is put in you're trucks computer that replaces the factory air/fuel tables. The monster exhaust may also be part of the problem since you need some backpressure to have power on the bottom end.