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Discussion Starter #1
Hope someone can offer some insight on this one.
The other day I got some fuel at a different station than usual. The next morning the truck developed a very bad vibration from idle to about 1200 rpm but disappears when revs are up. I thought maybe it was the fuel so I added more from my usual place and nothing has changed.
One thing I did notice, when I blip the throttle the oil pressure guage jumps all over the place. It never did it this bad before.
It's an '88 6.2 with almost 500 000km on the truck. Not sure if it's the original motor though. I'm worried that something is out of balance or a bearing may be gone somewhere.
I've got the truck listed for sale but will have to hold off now, until I can figure out what is wrong with her.
Thanks in advance for any opinions.
Neil
 

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I'd start by checking the harmonic balancer on the front of the crankshaft. Some were rubber dampened and can break the rubber causing a vibration. Left unchecked, the've caused broken cranks and blocks.

If the dampner checks out ok, I'd remove the drive belt(s) and start it. If the vibration is gone or changes, check the accessories. Could be water pump, fan, fan clutch, etc.

Early 6.2"s didn't use the rubber drive unit. Don't know if yours has it or not. Maybe somebody else knows what year they started using it. It may be, those with v-belts don't use the dampner and those with surpentine belts had the dampner. Somebody jump in here.....
 

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It may be, those with v-belts don't use the dampner and those with surpentine belts had the dampner. Somebody jump in here.....
Nope. My truck has v-belts and a dampener. I don't know much more about it, though. I thought they all had dampeners.
 

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I also thought all years had them.
 

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I think Fred is referring to the rubber lower pulley damper. It bolts to the harmonic balancer and has a large rubber center. I think it started use in either 1985 or 86. The earlier 6.2's just had a steel pulley bolted directly to the balancer.;)
 

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I know the 85-86 military 6.2 don't have this rubber on the dampner. Yep, as others stated, start by talking belts off and go from there.
 

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Discussion Starter #7
Thanks for the tips. I will try it with the belt off and see what I can find.
I do have the serpentine belt but no idea what the damper should look like to know if anything is missing. I did check it yesterday to see if there was maybe some mud on it throwing it out of balance but couldn't see anything out of the ordinary.
I'll check back in later with my findings.
 

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Yup, thanks for bailing me out Dave. I was talking about the rubberized lower belt pulley that bolts to the vibration damper. The only ones I've dealt with involved surpentine belts and broken crankshafts! Don't find many failed vibration dampers on 6.2's and early 6.5's.
 

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Discussion Starter #9
Well, I haven't found any problems with the pulley or damper. Rubber looks good with no cracks or separation from the pulley that I could see and there doesn't seem to be any gunk in the damper causing an out of balance situation.
I'm wondering if maybe it's just a bad injector. Once it's revving up the heavy vibration is gone.
I think it's maybe time to retire the truck and try a rebuild.
 

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i have the same problem
 

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Discussion Starter #11
Hi Hoot,
I never did find the problem and the truck is now off the road being parted out. I did however, have an injector line break on my Ford the other day and it developed the same vibration until it was fixed. My guess may be that I might have had a bad injector on the GM causing it to vibrate at idle.
Good luck
Neil
 
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