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][\][iCk0411, Fleet Manager
Category: Medium and Heavy Trucks
Satisfied Customers: 69
Experience:  310T Red Seal- Truck and Coach Technician
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I have a 2014 cummins isx400, it has a vibration in the

Customer Question

I have a 2014 cummins isx400, it has a vibration in the motor, it gets really severe under a load. 1250-1350 rpm
when it starts to shake violently and you let up on the throttle, it goes away for the most part. it only vibrates under throttle.
driveline has been checked several times and cummins ran all kinds of tests and it passed.
im lost
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  ][\][iCk0411 replied 1 year ago.

Hi my name is ***** ***** I would be glad to try and help you today. First off all welcome to Just Answer with your first question. I just wanted to take a moment to explain how the site works considering it is your first question. so the deposit they explained to you originally is only if you are satisfied of course. The experts like myself are freelance and only receive a portion of the proceeds if you rate the questions. So I like to let you know that i want you to be satisfied, if not then i will refer to another expert to help you further. Otherwise, I greatly appreciate a rating at the end of the question so that the site doesn't keep all your deposit.

So i wanted to start with a couple questions about your truck that you are experiencing the vibration with. Could you tell me what kind of chassis is this motor in? Is it a highway Tractor that pulls the same weight or is it a certain application? When the vibration happens where do you feel the vibration the most? the entire truck? the seat? the steering wheel? If you could elaborate the best you can on when it happens it would help me a lot. When you had the drive line checked is that all they did, or did they inspect anything else on the chassis? Does the motor have any fault codes or any other symptoms at all? Have you had any recent repairs at all like tires, diffs, transmission? anything at all? please take your time, the more information you can give me the better we can narrow down your issue. Thank you and I look forward to getting to the bottom of this issue for you.

Customer: replied 1 year ago.
No codes, every part of driveline was checked 4 times, it feels like it's coming from motor area. Even in nutrual let's say 1200 it vibrates, not bad but it does . It only does it under a load really bad were you think the dash is going to come apart
Expert:  ][\][iCk0411 replied 1 year ago.

10-4. So with the ISX I've seen a few things that could relate to the symptoms like that. First, most common cause is usually the motor mounts. Or, it could be just one of the motor mounts could be causing the vibration. Depending on the chassis and the transmission in your truck they typically have two rear motor mounts, one front mount. Second would be if you have a manual transmission it usually have a large bar, that mounts accross the rear of the transmission that allows it to move with torque but dampens the movement through the this bar.

I would recommend having those two components inspected thoroughly. I think your drive line is perfect considering you had it checked already and the symptoms you describe are definitely more towards the front of the truck like your thinking.

Customer: replied 1 year ago.
All the engine and trans mounts looks good, just got back from cummins and they did a overhead and it was good.They think it has piston slap.Motor runs good, it just vibrates, shakes violently under a load from 1250/1350 rpm in 10th gear, 9th is 1450
Customer: replied 1 year ago.
Let say your going down the road loaded, you go up a hill give it throttle and it starts to shake and vibrate bad, u let up on throttle just a little and it goes away for most part
Expert:  ][\][iCk0411 replied 1 year ago.

I'm thinking that its highly unlikely that the motor has anything internal wrong. It's going to be something simple the majority of the time. I would simulate torquing up the motor and having someone watch the motor from the side while its under torque to truly rule out the motor mounts. I've found that they can look perfectly fine but they are split and only separate when the motor is torquing like your experiencing. If you are hooked to a trailer leave the brakes applied on the trailer and just slowly release the clutch while someone is looking from the side of he truck ( in a safe position of course) The engine is meant to move a bit but you'll notice it will seem a bit excessive if the mounts are defective.

The piston slap they are reporting could be your air compressor. I've had every ISX I've ever maintained had a very loud knocking noise but watch to see if it's only knocking bad while the air is building. It will stop knocking once the air dryer purges and it stops building air. I like to look on the bright side and eliminate the very minor options first because 95 % of the time it is always something minor and not anything more serious.

Does your local Cummins have a dyno? or any other repair facilities around that could run it stationary? Unless Cummins thinks there is something genuinely wrong internally I would definitely recommend sending it back. Otherwise, it may need a stationary drive to narrow the symptoms. It may be worth the investment before it causes your truck any further damage.

Sounds like I may only be able to offer any further advise on where you could take it to get the diagnosis. Otherwise I want you to be happy with your diagnosis so if you have any other questions please shoot away.

Customer: replied 1 year ago.
Someone else told me this? How common is itRE: 2014 isx vibrationhonestly, what you are describing is too low of a final crank angle. This happens alot when tuning them and the timing is too far advanced for the amount of fuel your running. Now its more rare in stock cals, BUT ive seen trucks that overfuel from stock (drippy injectors, fuel pump actuator, wrong cal in the truck, etc) that do this. It's caused by the pistons hammering the crank less than 4 ATDC and you just hammer your rods into your crank and you get the famous big boy "Power vibration". on a stock truck you will not see if it is actually overfueling due to all the emmisions equipment.this is easy to test. flash the lowest hp file for your CPL and test it again - my bet is is mostly goes away. another option is to have someone manually retard the timing about 2 degree's and try again. My bets are it doesnt come back when this is done.many many people i talk to tell me they have been chasing this mysterious vibration for months and cannot find it. they think its driveline, rear ends, tranny, etc - but really its the engine destroying itself from the inside. rod bearings do not last very long with this condition. i just back the timing off a few degrees and its gone - but in a stock truck you will need to find the cause of this overfueling.
Expert:  ][\][iCk0411 replied 1 year ago.

This is of course possible but if this was the case it would of done this from the very beginning when the truck went into service. Calibrations just don't change and if the top end set was done then it would rule out any mechanical issues in the top end of the engine.

Has it always done this from when you bought it new?

I would recommend before getting Cummins to start calibrations on the motor and possibly tearing it down, rule out all your engine, and transmission mounts. As for the engine knock, run it with my advice to see whether it is the compressor that is knocking.

After those two issues are ruled out then I would book back into Cummins and make the recommendations on the calibrations. Depending on those results I would recommend seeing if Cummins has a dyno to run your truck on. Like the other gentlemen has mentioned you want to find this issue before it would do further damage to the truck.

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