It's Knocking, But Why? - Tearing Into Our 4.0 Jeep Daily Driver And Picking Through The Carnage

[@CoopersRepair]

Learned a long time ago that both the 4.0 jeep and 300 ford dont reeeally need skirts on the pistons. Just make sure you dig all the chunks out every oil change and keep going

[@craighansen7594]

Ha Ha! Just drop the pan and flush it clean a couple times a year.

[@CoopersRepair]

@@craighansen7594 on my 300 i never pulled the pan just fished out anything small enough to come thru the drain hole lol there is still quite a few big chunks in there yet

[@weinerdog137]

Lol

[@brainkill7034]

So true

[@greenbassboosts8872]

Well that's one more fun thing to look forward to in my 300

[@kevinshortell7604]

My '98 Wrangler busted a piston skirt a few years ago. I pulled the engine and my local engine guy rebuilt it for me, boring it 0.030" over. She's been flawless ever since. Jeep made a piston change in the latter half of the 1990s. 4.0s are known for it, but the 2.5s like mine can do it, too. With better pistons in my block now, it won't happen again. My engine was never abused in overrevved, but I have no regrets about rebuilding it. I've had it for 21 years and just keep on truckin'! 😎👍🇺🇲

[@elmerfudpucker3204]

Retired tech from Chrysler for 30 years, and I have seen this a million times. 4.0 pistons have a lot of pin offset to quiet them, and as a result they are prone to cracking the skirts when cheap gas and lack of maintenance is present. It doesn't take much detonation at all, to start the ball rolling on these engines.

[@alcartes6107]

Hey, Tony! Make sure you check the EGR and it's passages. Lack of EGR can lead to detonation as well. .

[@brainkill7034]

Had that problem on a mid 90’s maxima too

[@genehart261]

This is nostalgia. I remember my father-in-law doing rings and bearings on a six cylinder Falcon in about four hours. Gotta' love those inline sixes.

[@pauljanda5262]

4.0s are the best. My first one knocked like crazy. Drove great! And the detonation was almost surely overheating. It is an odd XJ if it has never struggled with temp.

[@iFixJunk]

Working on my XJ right now. This video was good for my soul.

[@davidmccrory5604]

It's videos like this that remind me why I subscribed to UTG . So interesting and reminds me to be sharp and diagnose fine details that are screaming information at you .....thanks Tony nice work son 👍

[@lilmike2710]

Same here 👍 He's like that shop teacher that loved his job and knew how to explain things in such a way that you're like, "oh, ok I get it."

[@MrJayrock620]

My first car had a pretty beat 3800 Series in it with 150000mi. The compression was likely crap and the rings were so cooked I had to run 20w50 to keep oil in it. But it ran well, and always started. It saved my bacon because here in Canada it hit -40C (also -40F) and being a southern car out of Arizona it didn’t have a block heater. My dads car was plugged in all night, and his didn’t start. Mine was so worn out it cranked right up and he had to take my car to work and drop me off on the way.

[@slackthompson6984]

distributor bushings ...........detonation , intermittent hard starting , broken starter housing .........etc prolly

[@mjh7879]

Had a 97, 98, 99, and a 2000 Jeep all with the 4.0. Loved that engine.

[@OldSchoolCrank]

Saw that happen on an old 1928 fire truck engine. The detonation past the rings was so bad that it deformed the piston, lost compression and sent the detonation into the oil pan. Found spider cracks in the pan. Great job Tony. Learned a lot from this video 👍🏻

[@WhiteTrashMotorsports]

I hate working on daily drivers

[@MrTheHillfolk]

It's such wasted time that's more deserved for my old cars.

[@thisisyourcaptainspeaking2259]

My garage queens need no repair.

[@teabag402]

SAME! I thought it was just me...projects I'll do anything daily...hate it so much..

[@Fljeff7]

Daily drivers only come in for 5k maintenance and service and are driven until next service interval can't do this not a daily it's a project, fact

[@MVPisME383]

My daily used to be my grandma and grandpa truck is the only reason it gets the little love it does get

[@mudduck754]

I quit doing it when it became work and it wasn't fun anymore. oh yeah and the massive stroke I had, where it took me 4 days to replace my starter on my Chevy 350 normally a 20-minute job and O'Reilly's parking lot with only a pair of vice grips cuz that's the only tool I had in the front seat, 4 days I guess you need two hands to do a starter.

[@jimforsyth2.]

Love the 4.0 manifold assembly there fun

[@tomchristianson]

Thanks Tony...

[@michaelking550]

Similar issue in my mid 80's f150 .. Ford used non forged pistons, in there trucks engine's..

[@harvestblades]

Uncle Tony I would love to see you cover rebuilding this 4.0! This was a fantastic video & is great info to know. I have two 2000 XJ 4.0 one my 16 year old son now drives that I have owned for six years & my daily which seems to have a cracked skirt & I use on some lengthy road trips for work. Love the XJ & 4.0 especially despite some of these known issues.

[@joecline3277]

I just finished building one of these motors in my 92 cherokee. 5 out of 6 pistons were cracked and 1 of thr 5 had completely dropped the skirt all the way up into the ring lands.

[@madmanmapper]

You're falling in love with the 4.0L

[@indianaslim4971]

I would definitely check all the rings and ring lands, detonation doesn't discriminate, it's all inclusive.

[@petediamond7263]

Why not do a three angle valve job when you have the head already off??

[@johnleinen7167]

Rebuilt a 2000 Cherokee 4.0 for a customer this year, #2 piston was broken ,bearings were perfect 201k miles found harmonic balancer had separated at bonding causing imbalance, some advice, don't use DNJ engine kit, chinese junk , use sealed power.

[@brandonburdette7895]

that jeep will out last any new jeep they make today

[@jack-nv3ty]

I did this same job last year. I fixed it the same way. It ran great. I did a lift put a set 35" mud tires I got off market place. I had a lot of fun with it and sold it to a young guy a view months ago. I'm now in the middle of LS swap into a JEEP Wangler JK I'm just doing a 5.3 with ax15 5 speed. never done a swap like this but I wanted to learn.

[@craighansen7594]

Talked to some guys that love that engine. They seemed to be in agreement that the same engine with carburetors didnt crack pistons.

[@therealsideburnz]

A man after my own heart referring to a 20+ year old Jeep as “late model” 😂

[@wastelander89]

I used use a 99 jeep cheerokee there my favorite jeep.they are small like a car but also have good handling and good 4 wheel drive and okay gas mileage. I put 180k miles of side street driving on that jeep it only broke down 1 time.but it was always enjoyable to drive . I hope I can find one again for a daily driver.there my favorite year and trim.mine was green.

[@slade9372]

I've been waiting for this teardown!

[@brianlevan339]

Thanks Tony! When are you going to hit on how you eliminated the weight on Bottle Rocket. Thanks.

[@Monaco-BuilditFixitDriveitEver]

Go back a couple years, if the videos are still up. He shows what he does to the car.

[@gadget73]

Always fix the problem, not the symptom. Have seen many people pay to have things "fixed" over and over because the real problem was never corrected. I'm too cheap for that, I want to fix things once and be done with it.

[@The_R-n-I_Guy]

I love working on my 1996 Buick Roadmaster sedan. When I can afford parts. But when you're barely getting by and you have a few hundred dollars worth of repairs that need done immediately. It kinda takes the fun out of things. Especially when you only have one car and you have to drive it to work. But other than that. I love working on cars

[@cerial0411]

70k is way longer then I could stand. I imagine you have a good radio. Open engine bay and easy to service stuff makes for much more enjoyable maintenance.

[@jonmoore8995]

Very good information. I like working on my daily driver because it's a 1964 Valiant.

[@1112223333111]

the skirt is over rev. running it with the piston tilted and broken probably pinched the lands

[@leerusch7392]

Change all six pistons. You don't want to have to do this job over again six months down the road.

[@minnesotatomcat]

I had a 92 wrangler with the 4.0, best driveline I’ve ever owned. I beat the piss out of it for a dozen years and in all that time I had to replace the water pump once and I had to eventually put a clutch in it, that’s it. It’s too bad they rusted so bad, you couldn’t kill them otherwise.

[@williamcavanaugh1415]

Is there actually a bad straight 6 cyl? Straight across the board from ford,GM and Chrysler, there all pretty much indestructible...

[@mtut]

They are all destructible. But mostly very tough, when used as designed. In the Chrysler world there is a lot of people complaining about the flathead 6 that's in the 1950s Power Wagons that have been in vogue. This flathead 6 was extremely durable - Massey Harris even used it in one of the best farm tractors of the 1930s, the 101 - but it wasn't made for high-rpm use. The Power Wagons were typically geared very low. Say what you will about the current consumer for 4wd pickups, but the designers of the Power Wagon clearly thought only an idiot would want to take a 4wd truck over 50 mph. Now everyone who wants a Power Wagon seems to be looking to build a bro-dozer with an intimidating highway presence. And the good name of the Chrysler flathead 6 is basically gone. It "has a weak bottom end." Bull. It's the easiest part to blame for a truck that had a very specific application in its time. Sooner or later, we will see some fool put a Hurricane turbo 6 in a Power Wagon and miss a curve at 90 mph because they don't quite understand what they are dealing with, beyond the hype and the image.

[@pisstoffcat5136]

I polished the crank on mine ,lost oil pressure but didn't spin the bearing , just the #6 rod bearing was showing brass and crank was ugly , I polished the crank with some emery cloth and small rope , got a .001 undersized bearing on #6 and 5 fresh standard bearings in the rods, a high volume oil pump and timing chain, put 50k on it till I wrecked it. Question, injectors being dirty and out of balance, cause a lean cylinder to cause this ?

[@MrTheHillfolk]

4:00 piston skirt is overrated. Besides, no skirt , no friction. Mpg gains,bigtime. Bust off all the skirts and get 63mpg highway,ask me how i know.

[@aprules2]

This is a great video UT. My friend drove his like that so long the piston broke and seized the engine. I pulled the engine expecting a broken rod of something. We had to sleeve the cylinder, the rest were perfect still. Not knowing the blocks changed from 97 I got a 80k mile motor from pic a part for $90 and found out we couldn't put it in. So we stole the pistons and rods out of it, along with a few other things put fresh bearings and timing chain in it and he drove it until the body fell apart. There's 3 things that suck working on your daily, having to get the work done on a time line, and working on any car newer than the mid 80s....

[@philchambers188]

uncle tony is sherlock holmes....amazing...i love it...

[@SkylerVahidy]

the thin side skirts is the common denominator in this piston issue. instead of changing one piston why not swap out all 6? you are already deep in this thing and you might have another one let go sooner than later? cheap insurance.

[@Monaco-BuilditFixitDriveitEver]

UTG loves to do things the most inexpensive way, and I’ll admit I do the exact same thing.

[@robertbriggs4176]

I'll bet he throws in a used piston. @@Monaco-BuilditFixitDriveitEver

[@autonomous_collective]

Analyzing Piston Failures To Determine Root Cause: Regardless of whether it runs on diesel, rocks a crazy rotary motor configuration, or is just a pump fuel-powered project car, every time an engine explodes, a thorough investigation is sure to follow. It doesn't matter which portion of the motor took a dirt nap. What matters is why it happened in the first place. That, and how much damage did said component's failure cause in other areas of the engine? All too often, people see a destroyed piston, and they immediately presume that the piston was at fault. When in actuality it could be any number of culprits. However, it's not always a big-ass explosion that causes a piston to fail. Oftentimes it's a continuous, gradual grinding scenario that is the harbinger of doom. For instance, contamination or combustion buildup can cause the skirt to start scuffing the side of the piston bore wall, thus leading to overheating. This results in an uneven ring groove, and a pinched ring gets stuck in a set position and will never float like it should. The piston can be a window into the engine's failure.

[@starionslider2116]

70k miles in 2 years? Impressive

[@RichieCat4223]

Engine ping is a shock wave that is moving at the speed of sound. That wave is bouncing back and forth in the cylinder, that's why you hear it rattle.

[@GeoTrashPanda]

I miss my XJ's!

[@cowthedestroyer]

Its just amazing when things just work and dont stop working because of a hiccup

[@tommymac3029]

The advantage of working on OEM stuff is that when you get done, it will likely work right on the first try. The negative is that room on newish Mopars is usually an issue. Much more room and simplicity on older stuff. Aftermarket junk is hit or miss, however. My guess for root cause is junk gas and a partially clogged injector.

[@craighansen7594]

Remember, the injector can be just fine but the o-ring sealing it to the intake manifold can shrink causing a localized vacuum leak.

[@connor3288]

I would def be putting in rebuilt injectors after that job

[@Lollygagger-k4p]

Owned a 96 Xj for eight years. Now I have a 95 Grand Cjerokee (ZJ). Both have the piston slap noise. Never a problem. I once read that Chrysler lightened the AMC pistons in part to go with the HO pkg, and the result was pistons sort of wiggling up and down the cylinder as they travelled. More than few broke or chipped the skirts with or without deton. If anyone can confirm this, I'd appreciate it. Rebuild suppliers seem to only stock one number for a standrat build, or I woud be able to compare the weight. I' can't find original AMC pistons tocheck.

[@stanleysgarage6405]

Trouble shooting at its best fine job

[@fairmont___d]

It's not worth replacing the other pistons while you're at it?

[@dalewarriorofthesea3998]

Anyone that has been in this automotive game for decades hits the wall,we all do I call it the biological stretched throttle cable lol Father time has his way

[@jeremypike9153]

Looks like carbon induced detonation. Notice the flat portion that comes close to a flat portion on the head. They didn't hit each other but they were close enough to share heat the carbon build up exasperated the heat causing the detonation to take place.

[@heaveymelt]

That was a great engine and pretty fun vechile dont see them much any more up here

[@timshamblin1223]

Check knock sensor and advance, or use premium fuel

[@Monaco-BuilditFixitDriveitEver]

Glib advice.

[@mtut]

1) Are you inspecting the other piston skirts? 2) Whether you do or don't, seriously consider getting the injectors flow-tested. Subtle differences in flow can cause intermittent detonation. There are places that will clean and test the injectors for about $150 and swap in good ones so you have a matched set. They need to be consistent and with a 1990s multiport system, it's not to be counted on that they even were consistent from the factory, plus whatever gunk they accumulated. It's a daily driver and you're about saving money, but is this Project Darwin Award? We just got done hearing about fuel starvation on Slaghammer.

[@MikeBrown-ii3pt]

Hey U. T. did you see the update on Steve Mags that posted on his channel today? If not, his condition is improving! He still has a long road ahead though.

[@saaskwatch5537]

Nice!

[@321CatboxWA]

I suggest a new distributor drive gear if not an entire distributor. Well done !

[@auteurfiddler8706]

Are you saying you are going to do this work in the car? Or remove the engine? I like this kind of repair where you save money by just replacing the bad stuff, not rebuilding the engine. I suppose a timing chain would be needed for this engine.

[@billwiebe6951]

Great video thank you for sharing one of the better ones I’ve seen

[@wastelander89]

Thanks for finally do a video on a mid 2000s daily driver 🙂

[@dogsense3773]

A few 2015 jeeps have come into the shop this year with 72-75 thousand miles on them with bad head gaskets with women driving them

[@ProblemChild-xk7ix]

Are higher quality pistons available aftermarket?

[@matthewcalifana488]

I was thinking the same thing . in which case six new ones , If oem ones are bad then that would be the way 2 go .

[@Monaco-BuilditFixitDriveitEver]

Just don’t get into detonation. Then you can run the least money into your project. That is the Uncle Tony way.

[@raiderjohnthemadbomber8666]

UT, it's not you it's the car companies. They've over engineered these things to the point that only a factory trained tech can get out from under the hood in less than six hours. This is why we stick to the old iron because they make sense.

[@deanstevenson6527]

🥝✔️🕊️🕳️ Usually, the injectors are only able to meter to 5% of ideal fuel load. The O2 sensor then allows pulse width to be varied to get target air fuel. When one injector goes off its ideal fuel flow rate, the rest of the injectors muck into to ensure the engine hits target air fuel. Just a simple check of the injectors flow rates can avoid knocking. In Australia, GM's US sourced GM3800 and Hi End V6s and Ford's six cylinder engines ran better quality pistons to ensure a bad injector or crook fuel didn't take out a position skirt. Piston skirt loss is a typical US in line six cylinder problem that GM, Chrysler and Ford hit with much better than stock US pistons. The HO Jeep 4.0 liter really needed better pistons with more ring gap and better.(forged) rods from day one, but it only had to meet the 300 hour test and EPA emissions, so they never went the next step up in piston quality like the overseas engines did. Always check your injectors first.

[@mtut]

Excellent point about injector balance. Late 80s/early 90s multiport injectors had lots of these issues and drivers didn't really understand how the engine could be running rich and lean at the same time. The other thing, psychologically, was that these engines - especially the 3800 - performed so much better than anyone expected; the 3800 also got really good gas mileage. A 3800 that had a 20% decline in power and a 20% decline in fuel economy was typically in an older person's car and still exceeding their expectations. But in reality it was sick. The lean cylinders in 3800s didn't usually get big detonation damage but they did burn valves and develop cracks in the heads. They wouldn't bring it in until it was missing and stalling.

[@GailUrge-vq6qn]

Excellent autopsy work . . . Dr. Coronet.

[@mikecollins8241]

I recently picked up a Cherokee ( my 4th!) and i know it'll need a rebuild at some point (it has 287k on it now) looking forward to seeing how you build this ;)

[@notajp]

That’s just getting broken in. My 98 with the 4.0 had well over 300k on it when I sold it. Still running strong, no knocks or smoke.

[@Motor-City-Mike]

We had more hard part failures from detonation than any other source.

[@billkendy4442]

Beauty! I always learn from your videos. I think your an awesome teacher, Thanks for sharing with us.

[@philchambers188]

waiting to see why plug was white...and chamber was carboned...???

[@EYE_SPIDER]

Really interesting, I like how you trouble shooted to see why did the piston break. Cool video Brotha! Boom Baby!!!

[@wlogue]

Nice! Those engines have a long lineage clear back to the Nash days, even before the venerable 258. A history dive may be in order! Cheers U.T.

[@GrimIndustry]

Include me in your list of 4.0 broken piston skirts. Happened to my ‘01 Cherokee 2 years ago

[@yamaharider825]

Got an 01 Cherokee too what did urs sound like before it cut loose? Mines got a rattle to it that goes away after it warms up a little sounds more like valve train chatter to me but I’ve heard a lot bout these skirts breaking and 4.0’s being noisy in general

[@GrimIndustry]

@@yamaharider825 mine had a slight knock, nothing serious and would almost clear up when warm. Then one day I pull up to a light and boom, sounded like a midget with a hammer under the hood. I think mine was piston slap from a sloppy cylinder and then it finally broke. The previous owner never fixed a vacuum leak in the emissions line from the fuel tank so it sucked dirt into the intake. I knew it was gonna need an engine sooner or later when I bought it so I just ran it till it gave out.

[@yamaharider825]

@@GrimIndustrythanks for the reply man eased my mind a little I think mines more a valve train issue

[@jayweiss4378]

A man who does know his away around the garage! Respect 👍🏻

[@brianandglendaharkin9457]

I use Lucas fuel ⛽️ additive 24/7 in my XJS and TJs life saver always use 98 octane . 👍🏻🇦🇺💯⛽️

[@chrisvandecar4676]

Late model has a knock sensor, no? Was the chicanery causing the det beyond the scope of what sensor, engine computer, available timing swing not enough? I mean just how FUBAR was the air/fuel/timing mix that it defeats modern efi? Inquiring minds want to know!😀

[@johnnoegel7394]

On my 2001 4.0 Cherokee I had cam bearings wiped out from a cracked head that allowed coolant to get in the oil. Oil pressure was ok cold but too low at operating temp. I had replaced crank and rod bearings to correct the knock thinking that would correct the oil pressure problem too. Engine sounded great but still had low oil pressure hot. Pulled the engine again and found the cam bearing problem. Check them cam bearings UT so you know they are good 👍

[@clint983]

0331 head casting number, had the same problem on a 2000 grand cherokee, New head and 8 years later still runs, just low oil pressure.

[@bobirving6052]

Thanks Uncle Tony. Great content. Maybe put another injector on that cylinder? Maybe running leaner than the others?

[@craighansen7594]

I saw that too, plugs a little whiter.

[@arindryn]

I love this type of content

[@colbytisdale3752]

The 3.9 v6 that they put in dakotas had problems with skirts breaking too

[@chisassinrollyoass2271]

I had the same jeep. Loved it. Had a 4½ lift on it and a drunk driver decided to park underneath my rear end while I was sitting at a light. That was the end of that

[@jodygarcia9892]

The end of the jeep or the driver?

[@frankirwin2377]

Great info Tony. Love your Detctive Work. Thanks

[@thomashodges6104]

Could it also Been carbon build up on top of piston??

[@Mr.Saltwater]

Weird thing I discovered when I had a 4.0. Dodge Neon injectors fit and atomize the fuel much better than a 4 hole. I think they are 8 hole. My Jeep ran much better.

[@Mr.Saltwater]

Just ran smoother, started easier, less noise. Didn't sound like a Dodge Diesel

[@mattryan9427]

So your saying it was possible fuel atomization?

[@Mr.Saltwater]

@mattryan9427 absolutely smaller droplets. Crank it with the injector out and it visible to you easily.

[@jamesstoy8967]

What years?

[@Frank-mt4qf]

Love your stuff bro. Very cool and informative

[@salspitz177]

IndaGoddenOfEaten

[@billferris5292]

At one time the 4.0's were so well known for piston slap they were nick-named the Jeep diesel.

[@shotsrodder]

Doctor Tony 👍 nice job

[@Mr.Saltwater]

I hate heavy engine work on newer stuff

[@kenleppek]

That was an awesome break down of not only what happened, but why. Good stuff.

[@richardcarelli7497]

Great Video!

[@AmericanSavageGarage-em2oy]

Excellent video.

[@FloydODB]

if you dont think another piston has a crack in it, you are dreaming

[@keithroute8906]

Way to go, hope it runs great when your done.

[@flipeecupsstuff7632]

I thought you quit smoking? I am glad you made this video I'll know what to watch out for on my 94 XJ

[@craighansen7594]

I would be concerned the other 5 pistons could be stressed enough to crack. Why not pop 6 new pistons in. You will already have the rods and pistons out. The plug on that cylinder looked noticeably whiter, it was going lean. Properly flush and test those injectors.

[@tonyc223]

Yep,put new pistons and new, better injectors. Can guarantee others are on there way out.

[@timmiller260]

Head looking for worpage and block i had head that was twisted

[@nickhahn3276]

Open and shut case. Great to see this kinda job without having to dust my knuckles. Thank you sir.

[@davidvincent2051]

Working on dailys sucks the soul out of me. But I gotta get to work.