Rough Engine Vibration

A few days ago i posted here becuase of what i thought was a rough shifting problem bc of the transmission but today i happened to rev the engine while it was in park. Amazingly when i reved the engine in park around 2200 RPM the engines decides to make weird vibration . If i rev to a higher point or lower point it doesnt make the same rough sound. In the mean time i have checked the air filter and i am not sure whats the cause. What can cause this and what should i check for ?

pete

NMI...need more info
year, mileage, engine, trans, 4X4?

Well its a jeep cherokee 94 auto with 115k miles Auto aw4 tranny with 231 tcase. Its also has the 4.0L engine.

This is something that started to heppen all of a sudden.

thx
pete

What about the engine and transmission mounts?

thats a good point but wouldnt bad mouunts cause it to happen at all higher rpms not just a specific one (approx 2200) and nothing higher or lower ?

pete

all mounts look ok...any other thoughts.

pete

Turned the jeep on on once again and noticed at higher RPMs the exhust sounds a bit like its coughing/popping like old muscle cars ?

Not sure if this means anything.

pete

Well today i performed the following things and they helped a bit...its still there but a lot less.

1. changed motor oil and filter.
2. drained tranny fluid and replaced
3. replaced spark plugs and wires
4. replaced heater valve was leakinng (i know it has nothing to do with this)
5. changed front diff fluid as it was discolored a bit
6.dumped a bottle of techron fuel injector clnr

Basically the same thing happens at the around the same time 2200rpm but less violently. Can the TPS cause crap like this.. Even tho i cahnged it recently maybe itd dead again ?

pete

jeepsrock said:

Well today i performed the following things and they helped a bit...its still there but a lot less.

1. changed motor oil and filter.
2. drained tranny fluid and replaced
3. replaced spark plugs and wires
4. replaced heater valve was leakinng (i know it has nothing to do with this)
5. changed front diff fluid as it was discolored a bit
6.dumped a bottle of techron fuel injector clnr

Basically the same thing happens at the around the same time 2200rpm but less violently. Can the TPS cause crap like this.. Even tho i cahnged it recently maybe itd dead again ?

pete

Click to expand...

This is kind of a reach but qualify the injector connections very carefully. If they are weak and/or intermittent, the cylinder will misfire and may vibrate like you describe.

Well the injectors were checked a few months ago so i dobt thats the problem, plus with another car i had an injector prob and it idled horribly.

Today i noticed a few things while driving it . It still makes the same type of vibration thats felt on the gas pedal and under the jeep but when i had someone press on the pedal while i am in front looking at the engine i sense no diff in sound or anything it looks normal ? I am no starting to think that i need to look at the exaust or some sensors ?

Anyone have any additonal suggestions,,

Pete

jeepsrock said:

thats a good point but wouldnt bad mouunts cause it to happen at all higher rpms not just a specific one (approx 2200) and nothing higher or lower ?

pete

Click to expand...

Not necessarily. It's possible, that the mount's are just in the beginning of chracking/braking. Though you don't see anything , under load(2200rpm or else) they might cause those vib's. Is any of the mount's wet, oily? Especialy the tranny/transfer mounts?
Have you checked all the mounting bolts? Engine to Bracket. What about the A/C, Alternator and P/steering pump mounts? Check'em for loose bolts.
Try this to eliminate the engine and tranny mounts from the list.
Take your floorjack, put a piece of 2x4 or whatever on it and place it under your engine, so that you can jack it up. Make sure you don't damage/bent anything.(oilpan, wires, etc.)
Now. Ask your buddy to start the engine, bring it up to the specific rpm's and keep it there. At this time you have to slowly pump up the jack. If the vibration changes, you're on the right track. If not, do the same with the tranny/transfer case. When you think you found it, lower the jack. The vibration/sound should change. Repeat it a couple of times to make sure.

Also check the exhaust mounts. (You might wanna do this before you check the engine mounts.)
First do a visual check of the mounts. Grab the exhaust and move it around, so that the rubber get's a little bit stretched. Next fire 'er up and bring it up to the vibration and slightly touch the tailpipe. If the vib's come from the exhaust, you should feel'em at the tailpipe.

Good Luck.


One more thing. Check the Torqueconverter bolts.

Well none of the mounts seem wet. I have checked the bolts on the other engine components and all is tight. I havnt tried supporting the engine and running it to see if its a engine mount prob yes bc of time.

I have checked all exhaust mounts (two in the rear and one on crossmember) and those are tight and have no more play than they should.

What i did do tho was while my bro was pressin on the gas i put a stick on the exhaust pipe in the rear and i could feel the vibration as he pushed the pedal.

Additionally i just cheked the flexplate bolts and theya re all tight.

I could be dreamin but the sound comes from the ground when i am driving and when i am under the jeep when its runin it sounds like its coming from the tranny/tcase area ?

pete

If anyone is interested i am driving the jeep now as i must to get to work and school. The problem is still present. The shift from 2nd to third seems to be effected as the vibrations and shift occur at that point.

I am still confused if this is a tranny or motor prob as it occurs in park and nuetral also. When checking the flex plate bolts the other day i decided to start the jeep with the cover off and take a look. I noticed that the plate wasnt spinning in a 100% perfect circle. It seemt like it was a bit offset in the way it spinned as it got lower nd higher as it span tho i am talking very small measurements. I also tried to pry the plate to see if there where any cracks but it doesnt seem there are any as it didnt budge at all except a small bit which i felt the torque converter move a ver very small bit.

I am a bit lost now, i have also checked the exhaust headers and there doesnt seem to be any cracks.

As far as the engine and tranny mounts does anyoe know how muh tey cost from the dealership ?

Anyone have any other suggestions or comments ?

pete

I actually had a chance to drive it for a longer period this morning and i must say that after 15 min of driving it got a lot better, i eamn it didnt go away completely but it was lessened. Before i arrived at my destination i put the jeep in park and revveed it and its still there but at a higher RPM like 2550rpm..Kinda strange.

pete

couple of other things to check
fuel filter- could be starving for fuel
cap and rotor

Ok 88 i will diffenately take a look at those as they are cheap things to look at. AS far as the flexplate i am starting to doubt myself as many ppl are telling me its cracked or damaged bc of the symtoms....what is a method i can use to check it without taking the tranny out ?

Pete

Tho today i went to a local mom and pop auto store and the counter guy told me motor mounts. He came with me to the jeep and told me to test them you must put the jeep in drive and pull the e-brake and put your legs on the brake and push the gas- as soon as he did this the drivers side of the engine launched up a bit. He then proceeded to tell me it could be the drivers side engine mount.

On the way home now its getting worse...i am guessing because of the stress caused by the direct launch at the store the mount is getting worse....tho i am still not a 100% sure if this is the prob ?

And the guy proceeded to sell me ones at the counter made by anchor for 17$ a piece and 30$ for the tranny one ? Should i buy these, or buy ones at rubicon4x4.com made by omixida close to the oem ones ? or should i not consider this being the issue all together.

pete

read above .

OEM engine mounts are just fine, unless you do some serious rock crawling or the like, where engine torqueing on the mounts is an issue.

Most of the aftermarket mounts that use polyurethane are MUCH stiffer, resulting in more general drlveline vibration being transmitted into the body.

Well I looked at the flexplate once more very carefully and i pried on it as well and it seems that its pretty stiff.

I went ahead and got prices for motor mounts from 4 places kragen, autozone, small shop and napa which were all in the 20-30$ per mount. The stealer wanted 55$ mount whihc was too much for m at the moment as i have spent too much on this jeep as it is, especially for a poor college kid..lol

The ones at kragen, autozone and the small shop were all anchor brand which i heard negaive things about. I decided to purchase the napa ones which where napa/bk brand. Look at thi pic and you can see that they look like descent quality units.




Additionally i purchased their napa tranny mount which had a tilt in it like the stock unit did.

It took two ppl about 1hr two replace all three mounts. Despite what i said about them earlier looking good the driver side mount was cracked all the way thru and eaten away on the other side, while the passanger mount and tranny were ok, but i still repalced them.

Driver side Mount:





I havnt driven the jeep yet a lot but i think this may be it. I will let you guys know.

I would like to thank everyone on this forum who responded for their suggestions and feedback. I hope this is it, wish me luck.

pete