Popping Sounds Under The Floorboard Under Full Throttle

Okay so I have a 99' XJ with the 4.0, AW4, and NP231. I list the drivetrain because i'm not sure if it might be drivetrain related. It also has a three inch leaf and spring lift on 32s. The problem started a few months back after I took it on a day trip, and now whenever I'm at a dead stop and give it 90%-100% throttle it starts popping very consistently. I could get under it and move the t-case and transmission with my hand so I thought the transmission mount was broken and replaced it with a new Duralast mount but it still seemed to do it. It also pops and makes unusual sounds when i turn sometimes which i thought might be a busted upper control arm bushing but it seems pretty good when I looked at it.
I'm at a loss now and don't know what to do and I don't want to keep wasting money on stuff that doesn't need to be replaced.(I'd rather waste it on bigger jeep parts:laugh3 It is really irritating and any input would be very appreciated.:yelclap:

bad motor mounts, causing your drive shaft to hit exhaust? or in my case i had the trans crossmember installed backwards, moving the trans towards the drivers side, causing my front driveshadt to start hitting my upper 02 sensor,

other thoughts could be loose exhaust parts, bad universals in your drive shafts, front axles. do you feel it at all in your steering wheel? you could pull the front drive shaft and drive it and see if it changes

Suspect: motor/transmission mounts, suspension bushings, loose u-bolts or other suspension bolts loose, drive shaft interference, exhaust interference or failed exhaust hangers, u-joints binding, worn transfer case chain, differential spider gears, Limited Slip differential clutches.

Can't really help but pulling the front driveshaft and test driving would eliminate a few options. I'm thinking front driveshaft U joints or double cardan joints. This test would rule that out.

I can feel it in the gas pedal and under my feet. But I’ll pull the front driveshaft tomorrow, maybe that’ll help figure it out. Thank y’all for the input. Very appreciated.


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I’ve been busy running errands and what not but I finally pulled the driveshaft and it seems it only pops once under heavy load whereas before it would pop continuously. I also hear a slight squealing under heavy load. Any input on that?

Also it seems I’m still have a separate problem when going slow and turning sharp, like coming in and out of my driveway. It makes a pop and crackle kind of noise Maybe upper control arm bushings? I put it on the lift and they looked decent. Probably going to replace those next. Really lost here.

Again any input on either problems would be very appreciated.


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Here is what we have for facts so far, " My Jeep makes some noises underneath ......".

You need to do some research and determine some of the more common XJ Cherokee issues, and more importantly, how to diagnose them. Pinpointing the source(s) of the noises will greatly help in diagnosing the root cause of the noises. Parts seldom do not "look good," so you will have to perform some basic troubleshooting and diagnostic inspection. If you are at a total loss, find a local 4x4 shop or independent locally owned frame suspension and alignment shop to help out. Randomly shotgunning new parts at an undiagnosed problem seldom has good results, and it gets expensive real fast.

I haven't seen this on a Jeep but the noise you describe sounds exactly like what I experienced with a worn universal joint on the drive shaft on an old Chevy. If you take the driveshaft off again try working those universal joints really hard to see if you get any play.

Like I said, before I removed the front driveshaft the popping noise would be continuous and constant under full throttle but since I removed it, it will only pop once and be done. I thought this was a weird coincidence but I’ll check the u-joint just in case.
Thanks.


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I guess I should also add it’s stock except for a 3 inch lift and 32s, no SYE so that might not be the best for the driveline. Lol


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double cardan centering yoke is yet another option.
rear shaft joints
could be ball joints
control arm bushings
trans mount
engine mounts

need a little more info!

Alright thanks Denvard, think I'm gonna replace the control arm bushings next. My dad also gave me a motor mount for Christmas that it needed so maybe that'll help as well.:laugh3:

cherokeecrawler said:

I guess I should also add it’s stock except for a 3 inch lift and 32s, no SYE so that might not be the best for the driveline. Lol

Click to expand...

At 3", 97+ XJs need a SYE and CV driveshaft, or a transfer-case drop, to eliminate vibes.
A TC drop increases the angle of the front driveshaft's CV joint, making the SYE a better choice, with greater ground clearance .

I forgot I did do a TC drop with some spacers my friend made. I also got some bushings and a motor mount to throw at it soon so maybe that will help.


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So I finally got to work on it over the weekend and when the motor mount was pulled, the metal sleeve came completely out of the rubber with the entire top piece of the rubber missing. Still have clunking noises up front so I'm hoping it's the upper control arms since there's some ordered from RockAuto. Don't know when I'll get to replace those but I'm hoping it's the last of my problems.