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Unread 07-11-2013, 08:45 AM   #1
oldschool88
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1996 Cherokee 89k and started knocking tapping on cold start

Just picked up a cream puff 1996 Cherokee with 89thousand miles on it.
no rust dents or anything.. When I got it I was super stoked that it had no knock when cold or at idle. The jeep had sat for a couple years Ina garage with out being driven so first thing I did was change the oil for the trip back to Michigan From Chicago. Once drove the 400 miles back to northern mi the jeep has developed a very small tapping/knock on cold starts.. It goes completely away once the jeep is warm or 4-5 mins of idle time.. Could this be the sythtic half blend of oil ? Oil filter ? Or could the jeep need the rocker bolts tightened a little bit, if they loosened up a little. My last jeep "2000 Cherokee" had a tick knock tap for quite sometime Around 60-70 thousand miles is when it started and I drove it till it hit 320k ,just parted it out last month ' rusted frame rail, oil pan, floor boards and lost compression in a cylinder causing it to run very very rough at idle.. I'm just wondering if I should run a certain type of oil to calm this tapping noise down or if I should just consider it the nature of the beast to make this noise.. Thanks for any help guys

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Unread 07-11-2013, 07:16 PM   #2
AZ Jeff
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There a multiple types of "tapping" in the 4.0 Valve train tap (usually a sticking lifter) is sharp, and is easy to detect with a stethoscope or the old broomstick trick. Piston slap is more subtle, and tends to diminsh as the engine warms.

I am betting you have piston slap, which is common and harmless in the 4.0 The best way to verify this is via the stethoscope.
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Unread 07-11-2013, 08:00 PM   #3
Charley3
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Jeff may be corrext.

However, I have owned 2 XJs low 30sK miles and they tapped at cold start. So did a brand new LJ with 11 miles on it. In fact, the new 4L tapped the most.

The fuel injectors are noisy tapping machines at cold start. Maybe the valve train too. And that when new.

Isn't going to improve much with age.

Mobil One synthetic 5/40 will quiet the valvetrain some. Might even help piston slap?

The injectors are still going to make noise, especially at cold start, no matter what.

Even in perfect condition, it's a noisy engine.
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Unread 07-12-2013, 08:18 AM   #4
oldschool88
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Thanks guys. I just bought a 1996 parts jeep with a good rebuildable motor in it.. I'm going to put the motor in the garage and rebuild it in a couple years, of the knock gets progressively worse.. Thanks again for the help guys..
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Unread 07-12-2013, 11:22 AM   #5
tbburg
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You might try treating with Seafoam. (1/2 can in oil, drive for 200/300 miles, change oil and filter)
A lot of times, the tapping is caused by low oil flow into the lifters from buildup in the galleys and passages in the lifters. When the oil is cold it can't flow into the lifters fast enough and they partially collapse. When it thins out after warmup the the lifters get full volume and the tic stops. I've read several people who have had luck with this fix, and it worked for me.
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Unread 07-12-2013, 12:40 PM   #6
mickc9129
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Take a look at your exhaust manifold for cracks, broken bolts or a gasket leak. The initial sound of the exhaust leaking sounds like a bad tappet. Then when the manifold heats up it expands and seals the crack somewhat to eliminate that noise.
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Unread 07-12-2013, 03:32 PM   #7
Charley3
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Quote:
Originally Posted by tbburg View Post
You might try treating with Seafoam. (1/2 can in oil, drive for 200/300 miles, change oil and filter)
A lot of times, the tapping is caused by low oil flow into the lifters from buildup in the galleys and passages in the lifters. When the oil is cold it can't flow into the lifters fast enough and they partially collapse. When it thins out after warmup the the lifters get full volume and the tic stops. I've read several people who have had luck with this fix, and it worked for me.
That ^ would work. However, my suggestion will also work.

My Mobil One 5/40 suggestion is a different approach to same issue. Its 5W at cold start. So near intant oil pressure. So oil flows to lifters very fast. Quieter at cold temps aka cold start.

At full op temp its a slippery synthetic 40W, which quiets things be being very slippery and the higher weight oil cushions things, which quiets them.

All Mobil One oils have a lot of detergent. The 5/40 is for turbo diesels. So even more detergent. Within 3000 miles it will have your engine very clean, including the oil passages and lifters.

The only caviat with switching to a synthetic oil (especially a diesel oil) is change the oil filter at 500 miles, and then again at 1000 miles the first time you use synthetic oil. Then change filter again at 3000 mikes.

This is because the high detergent oil cleans and loosens so much engine deposits that your oil filter won't last 3000 miles.

---

On your second oil change you can go to normal (for syn oil) oil and filter change intervals, which is change oil every 9000 miles, and change filter every 3000 miles. That is changing often for syn oil (especially a diesel syn oil in a gas engine).

You could change oil every 12,000 miles and filter every 4000 miles. Even that is often for Mobil One 5/40.

I think I recall Mobil recommends changing oil every 18,000 miles and filter every 4500 miles, which is adequate. Even this change interval is more protection than a conventional oil offers.

---

Mobil One 5/40 is very affordable when you use any of the above change intervals.

It will clean the lifters so well that Seafoam won't be necessary for lifters.

Also, Mobil One 5/40 will offer superior lubrication for entire engine.
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Unread 07-12-2013, 03:43 PM   #8
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Also remember that the injectors make ticking noises that sound a lot like tapping, and that's normal, even on a new 4L engine.

It'll never be quiet, bu it might be less noisy if other possible issues are addressed.

Though there might not be any other issues/problems.
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Unread 07-17-2013, 07:11 PM   #9
oldschool88
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Update - I changed the oil to 10w 30 royal purple with a wix filter.. I always seem to bust off the oil sending unit on everyone of my jeep at some point during ownership , so I rode the bike to the parts store . Got home replaced the part , added the RP oil and started it up.. Sounded louder and the knock presented its self after warmed up ,I was getting furious.. Then my dad stopped by. We went for a ride and he wanted to see what kind of power the jeep had compared to his wrangler. I floored it and reached about 75mph in no time.. When I got home the knock had disappeared and the engine seems to run better than ever.. I also would like to note I put a quarter bottle of marvel mystery oil in before the oil change and drove it for about 50 miles.. The knock is still there, but not nearly as loud and nearly as long, more of a tap now. Hope this helps a couple people , I am going to check the flywheelbolts when I get a chance. Maybe that is where this faint knock is coming from, who knows. The jeep runs outstanding and I am just going to deal with the noise if I can't track it down.. Thanks for all the help guys..
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Unread 07-18-2013, 06:13 AM   #10
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Quote:
Originally Posted by oldschool88 View Post
Update - I changed the oil to 10w 30 royal purple with a wix filter.. I always seem to bust off the oil sending unit on everyone of my jeep at some point during ownership , so I rode the bike to the parts store . Got home replaced the part , added the RP oil and started it up.. Sounded louder and the knock presented its self after warmed up ,I was getting furious.. Then my dad stopped by. We went for a ride and he wanted to see what kind of power the jeep had compared to his wrangler. I floored it and reached about 75mph in no time.. When I got home the knock had disappeared and the engine seems to run better than ever.. I also would like to note I put a quarter bottle of marvel mystery oil in before the oil change and drove it for about 50 miles.. The knock is still there, but not nearly as loud and nearly as long, more of a tap now. Hope this helps a couple people , I am going to check the flywheelbolts when I get a chance. Maybe that is where this faint knock is coming from, who knows. The jeep runs outstanding and I am just going to deal with the noise if I can't track it down.. Thanks for all the help guys..
You beat me to it!! You had a sticky lifter. If it happens again on start-up, shut it off for 30 seconds and re-start it. If it's a lifter, chances are the noise will be gone.

Shine a light into the oil filler hole and note the amount of sludge build-up.
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Unread 07-18-2013, 11:40 AM   #11
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Originally Posted by cruiser54 View Post
You beat me to it!! You had a sticky lifter. If it happens again on start-up, shut it off for 30 seconds and re-start it. If it's a lifter, chances are the noise will be gone.

Shine a light into the oil filler hole and note the amount of sludge build-up.
I am thinking that you have a sticky lifter as well.

I had virtually no problems with my 4.0, except for smoking when it was warm, until I had put in some Lucas oil additive to help with the smoking problem, and the age of the motor (189,000 miles). Soon after that I had one of the noisiest lifters at start up that I have ever had. What had happened was that the thicker additive, combined with the sludge build up within the lifter, was preventing a good oil flow, thus not allowing the hydraulic lifter to "pump up" properly. I have since addec a quart of transmission fluid, then ran two treatments of motor flush with each oil change. Thankfully the lifter noise has cleared up.
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Unread 08-08-2013, 05:08 PM   #12
oldschool88
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Well the noise is back... I haven't drove the jeep for a week or so. started it up and about 3 minutes after a quiet idle it started knocking again.. slowly getting louder as it reaches temp.. The knocking goes away once rpms reach about 1000-1200. the jeep drives and runs great, no misfiring or stumbles.. its not really loud, but a noticeable knock. when i drive down my block and stop at the stop sign it seems to be worse than before.. could this be piston slap ? i know it is very common and usually presents it self when the engine is cold, can it also present itself when the engine is hot? .. my buddy is a mechanic and he thinks its a piston, says "jeep made pitons metric and messed up" or something like that , he's not the smartest person i know.. so he was basically saying its piston slap. Im just not sure what to think.. i don't want to blow a piston skirt or piston while i'm 100's of miles away from home..
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Unread 08-08-2013, 05:44 PM   #13
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Auto trans? What brand of oil filter are you using?
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Unread 08-08-2013, 06:14 PM   #14
oldschool88
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Auto trans , using mopar filter... tried different oils - pennzoil yellow bottle 10-30 with percolator filter , royal purple 10-30 with wix filter and last mobile one high milage with mopar filter. really no affect on the noise with different oil.. I also checked the flywheel bolts and they are tight..
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Unread 08-08-2013, 10:39 PM   #15
AZ Jeff
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Quote:
Originally Posted by oldschool88 View Post
Well the noise is back... I haven't drove the jeep for a week or so. started it up and about 3 minutes after a quiet idle it started knocking again.. slowly getting louder as it reaches temp.. The knocking goes away once rpms reach about 1000-1200. the jeep drives and runs great, no misfiring or stumbles.. its not really loud, but a noticeable knock. when i drive down my block and stop at the stop sign it seems to be worse than before.. could this be piston slap ? i know it is very common and usually presents it self when the engine is cold, can it also present itself when the engine is hot? .. my buddy is a mechanic and he thinks its a piston, says "jeep made pitons metric and messed up" or something like that , he's not the smartest person i know.. so he was basically saying its piston slap. Im just not sure what to think.. i don't want to blow a piston skirt or piston while i'm 100's of miles away from home..
The fact that it went away and then came back points to a sticking lifter, and not a piston slap issue.

And by the way, a 4.0 can have pistons that slap for 100K miles with no harm. They are kinda noisy in the piston skirt area compared to many other engines, but it's harmless.
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