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Vibration at speed after injector replacement, 2005

1054 Views 2 Replies 2 Participants Last post by  fortyfive2life
My father in law has a 2005 Cummins 5.9, completely stock. He hauls commercially with it, and maintains the truck really well. Recently he had an issue with a bad fuel injector, so he took the truck in and had it replaced.

Now after his latest trip he says the truck has a bad vibration right around 55 mph. He says if you hold the speed around 55 to 60 mph, the truck runs very rough, and has a noticeable vibration. When he accelerates it is smooth, even while moving up through 55 mph. It also does not run rough at idle, he says it's smooth as glass. No codes according to the local repair shop, they don't even know what to look at.

If you need more information let me know, as I'm posting this second-hand. He'd be grateful for any thoughts you guys might have as to what he might need to look at. Thanks all!
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If it had one bad injector it probably has more. Trying to swap out one just introduces the potential for a greater imblance with the others.

Have the shop run a cylinder contribution test then a kill test on each cylinder. Line the results up in firing order noting percentages on contribution and rpm drop on kill test.

That will give them an idea what the balance looks like.
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thanks for the reply Cerberusiam...I passed on the info, and he's going to take the truck in to see if his shop can run those tests. I think he knows he should replace all the injectors at once, but that's a pricey trip to the mechanic so he was trying to get by with one. Again we appreciate the suggestion as to what to try!
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