Vibration problems

[MrBSA]

Hi, I am looking for some assistance with diagnosing a very annoying vibration problem in my 2002 6.6 Silverado. I have recently noticed this heavy vibration at idle and just off idle. It comes up through the seat, steering wheel, and pedals. The problem goes away or at least is not noticeable once revs are up. I am wondering if this is an engine mount problem or injector misfire or something. I recently had to take the truck through it's bi-annual emissions test and it passed with ease so not sure if injectors would be the problem although the engine is noisier now than it used to be especially under load. I had put this down to the synthetic oil I switched to useing which is Mobile 1 15-40 diesel and says it is recommended for the Duramax.
According to my truck history printout there was a left and right upper cushion/body shim replaced by the original owner at 48,500 Kms (part # E1103 E1104). Would this be something to do with a vibration problem previously? The truck now has about 178,500 Kms on it and appears to have the original injectors although according to the printout the fuel tank pump module was replaced at 30,800 Kms Truck has also had the powertrain control module reprogrammed with SPS at 57,000 Kms. What is this SPS and am I up to date with programming??
Any insight into my vibration problems would be appreciated. Thanks in advance.
Cheers,
Bruce
2002 Silverado Duramax extra cab short box 2wd

[crafty]

Is your truck a standard or Auto?

If you have the manual trans you may have a flywheel out of balance. I had the same vibration problems as you describe before I had the flywheel replaced.
If you have an injector that is not working it would be smoking at an idle. At least that is what mine did when an injector quit on me.

I have 186,000 on mine and 5 of the injectors have been replaced. A check with a scan tool will tell if all of them are workig correectly.

[MrBSA]

Yes I forgot to mention the truck has the Allison Auto in it. I am leaning towards the problem being a body mount or engine mount as the truck does not smoke at idle or any other time except if I really stomp on it and then I get clouds of black smoke. Again the vibration is only at idle or just off idle but is very noticable to point of being really annoying. Was hopping someone else had had a similar problem and could point me in the right direction.

Thanks,
Bruce

[royalglen]

It may sound strange but we had a bad vibration in an older GM truck--changed idlers,air conditioner bearings,etc under warrant---we discovered it was a poorly formed serpintine fan belt--the ribs had rubber slag in spots in the grooves-vibration started when Alternator siezed and burned the old belt off.and a new belt was installed.