Rumbly Grumble

So Ive got an Xj running on 31's and a 3in right now, currently no mods on the engine, but since i got it it has had an awkward shaking/rumble when i idle... i dont know if any of you Xj doctors know what this is (probably do) but id love any thoughts on solving this, i know its no biggy, but id like to know whats going on. Thanks beforehand!
Cheers :cheers:
Mike

i've seen some off the wall thread titles... "rumbly grumble", hilarious:roflmao:

check ur motor mounts... what's "awkward" about the "rumbly grumble":shhh:?... is it not a steady rhythm?

xj^REMY said:

i've seen some off the wall thread titles... "rumbly grumble", hilarious:roflmao:

check ur motor mounts... what's "awkward" about the "rumbly grumble":shhh:?... is it not a steady rhythm?

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well thanks first for a swift reply... thats a good idea, i will check those, but it seems to me (porbably should have said it first) like it might actually be coming from the back, like the muffler bumping around, or im just a fool, not 100% sure but yes, not a steady rythm. Is that fixable by a engine tune?
I keep looking like this to find exactly where its coming from.. :shiver:

no offense, but u sound young & unfamiliar... we've all been there, so dont be insulted... muffler/exhaust towards the rear, wont cause the the vehicle to "shake"... physical vibrations/"rumble" at IDLE, can only be explained by engine combustion, & it'll obviously be in the front end... if it's from the rear, at idle it'll be exhaust related... could be a leak in the piping/muffler, or hangers if u hear a metal "clanging"

also might be a good idea to let it be known what year (pre-91's are renix, pre-97 are High Output 4.0L 6 Cylinder "old" body style, 97-01 are "new" body style, difference in 99-01 were re-engineered ignition & exhaust), transmission (3 different manual trans', post 91? is the most common ax-15, all automatics are aw4), transfer case (242, with all-time 4-wheel drive, 231 is part-time only), axles (all factory xj's came with the dana 30 up front... in the rear would commonly be either dana 35 or chrysler 8.25... if u have ABS, it has d35... some "old"/early models came with dana 44 in the rear)...

thats just a little important "head start" info for u... this is what u should tell us when u need engine/transmission/intake/exhaust/electrical/cooling help/info... the fact that u have a 3" lift & 31's isnt necessarily important to these areas, & especially at idle

yeah, you hit it pretty much on the button, i have some general knowledge but not very deep into a lot of the engine issues. Its a 2000 Sport. Auto as well, so i guess that Means aw4. but thank you for the help/info Remy

The vibration may be a rough idle...causing the engine to move on the motor mounts...worn out mounts will let the engine to shake, which in turn may make the exhaust rub/rattle against something in the rear. So, it is possible to have a vibration that is caused up front, but heard from the rear. Just ask me how I know!

Flyfisher said:

The vibration may be a rough idle...causing the engine to move on the motor mounts...worn out mounts will let the engine to shake, which in turn may make the exhaust rub/rattle against something in the rear. So, it is possible to have a vibration that is caused up front, but heard from the rear. Just ask me how I know!

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Actually, that was what i was suspecting but i thought it sounded rather absurd. im gonna try tightening them mounts, hopefully not replacing them. you guys are the greatest arty:
-Mike

how does one go about tightening it? am i supposed to try to tighten the bolts that go to the frame? or the ones that are horizontal? sorry for the dumb question....

I'm not sure if those can be tightened. Typically when the mounts go bad and are "loose" it's a failure of the interior portion of the mount. Since OEM mounts are relatively inexpensive I'd look at replacing them or step up to something like MORE or Brown Dog motor mounts.

Worn/broken/loose motor mounts on the XJ's can cause exhaust cracks (typically in the exhaust manifold), and when the mounts get very bad, the cooling fan can shift into the rear of the radiator causing a large rupture.

Friendly tip: Because the XJ's are what is commonly called a unibody, some people get touchy around here when people mention the word 'frame' when discussing XJ's.

thank you very much snake, and i will correct my self now if a may, "body" not frame =P
thanks for the help everyone

Is your check engine light on? Sounds like it could be misfiring? Take it to autozone or o'reilly's and have them scan it. Its a free service btw.

no engine light, i was thinking of tuning soon though

It sounds to me it could be a possible misfire? Is your check engine light on? If so scan for codes.

Have you checked spark? fuel pressure? check those before taking to a mechanic for a tune up. Could be bad spark plug or wires?

kevswens20 said:

Could be bad spark plug or wires?

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It can't be wires--no plug wires on a 2000.

For what its worth, this OP isnt crazy. I do know a lot about vehicles and I have a 2000 Sport as well with the chry 8.25" and I have a "rumbly grumble" sound coming from the rear at idle in drive. I cant figure it out. Im thinking it may be some slack in the u joints and the driveshaft is bumping around when im stopped at a light.

wow, forgot about this post, ended up being my muffler contacting the unibody, i only had one hanger for my exhaust. i fixed this a long time ago. thanks again tho everyone

poppyseed said:

For what its worth, this OP isnt crazy. I do know a lot about vehicles and I have a 2000 Sport as well with the chry 8.25" and I have a "rumbly grumble" sound coming from the rear at idle in drive. I cant figure it out. Im thinking it may be some slack in the u joints and the driveshaft is bumping around when im stopped at a light.

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driveshaft shouldn't be moving at all when you're sitting at a light-- check your exhaust a little closer. I'll bet that it's either vibrating on the trans cross member or on the "frame" rail next to the fuel tank. :wave:

Try pushing the transfer case shifter forward and see if it goes away.

Shorty said:

driveshaft shouldn't be moving at all when you're sitting at a light-- check your exhaust a little closer. I'll bet that it's either vibrating on the trans cross member or on the "frame" rail next to the fuel tank. :wave:

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You're probably right, i do know the u joints are worn though, i was thinking the vibrations at idle (mine idles a little rough sometimes, still havent figured out why) might be reverberating into the drive shaft. but once in neutral or park it doesnt do it all.