for the high milers with a 4.0 - a Q

This is a question for those with 200k+ miles on their 6 cyl 4.0...

I have 2, both over 250k miles. One has a ticking sound coming from inside the engine at idle. Sounds a bit like a VW diesel, but more pronounced if under the car or against a wall to reflect the sound. Most times you can't hear it inside, and sometimes itis a little louder than others. Only hot, not cold. I put a 160 stat in it and its still there (fyi). It isn't a ping, doesn't sound like valve tap at all, doesn't sound like main bearing, goes up with idle, but quickly goes away as engine noise gets louder. An engine flush may have made it louder (not sure). It's hard to pinpoint, but sounds more like the rear of the engine rather than the front (used a stethoscope).

Not to prompt, but I guess it could be piston slap, but it isn't quite like any piston slap I've heard before, so I can't be sure.

I've also noticed a similar tap in the other XJ, but very faint. You almost can't hear it even up close, and would miss it if you didn't hear the other and be on the lookout. So it seems to be in both at about the same miles. I hope it's normal and safe...

The question is - does this sound familiar to anyone? Is it common at this mileage for this engine? I've only had each after 200k miles (both) so I can't talk about how it was raised I'm hoping it's not only common, but can be disregarded for the next 500k miles!

So, anyone else got this? Any trouble because of it? Know what it is?

Thanks,
Skip

engine noise

I'd (ALMOST) guarantee it's a loose timing chain, I have had this noise on both the 2.5 and 4.0 engines after about 150k. It is common, and described as a diesel noise. I bet you have been asked "is that a diesel Jeep' or been told," hey your engine is gonna blow up.".It's an easy repair and it will be really quiet, so much so that you will hear all the other noises you haven't been.Doesn't cost much either, a timing cover gasket, chain set and some work and you're fixed up.Biggest deal is getting off the crank pulley.Be sure your timing chain cover isn't grooved or cut, as some with a lot of chain wear will do this.JB Weld will fix this though.If that isn't it, all I can say is check the bearings, you can do those with the engine in the Jeep .I still bet it's the chain based on years of experience.But you will know for sure if you listen to the cover, I think.

Without hearing it directly, and reading your symptoms (and having an 88 with 280K on the clock, an 87 with 230K, and two 89's running 160K and 185K,) it sounds like a tappet knock to me. Have you a mechanic's stethoscope? If not, you can get them at Sears for a few bucks.

You can then work to isolate the noise more directly - a mechanic's stethoscope has a longish probe on it, so you can work in finer resolution to isolate noises.

There's a slim possibility it might be an injector getting loose on you (which will probably want changing, especially if they're 1990 or older...) since they can "tick" as well. However, they're more likely to tick all the time.

The reason you're hearing it more when the engine is warmed up is because the oil has thinned, and that can show a lifter that isn't "pumping up" properly.

The bad part? You have to remove the cylinder head to change them.

Since the oil pumps up to the top of the cylinder head through the lifters, a lifter that isn't pumping up is also not pumping enough oil up top - while it probably won't lead to a catastrophic failure (probably - anything is possible!) it is more likely to cause a failure than not, so it should be addressed fairly soon.

However, spend the ten bucks on a mechanic's stethoscope and try to "locate" the noise a little more - it's one case where ten minutes of troubleshooting can save you several hours of work. Make sense?

Thanks for the ideas. Like I said, I used a steth on it. Came strongest from the rear oil pan, but also rear valve cover, front pan, and such. Not from the head or block. Could be just that the sound traveled through the thinner covers because ticks have higher frequency components.

I didn't try the chain cover directly, but will. That will be a simple and sure test. It doesnt' sound like a lifter, but it could be I'd guess. If it's the lifter, I've heard worse. The valve cover shouldn't be too tough to remove, but I'm not looking forward to it.

I did try a bottle of STP - had to put it in boiling water to thin it enough to pour in a reasonable time. It seemed to make it louder. Cold, it's quiet. After several weights, 40 or more makes it louder, 20 or 30 a bit less it seems.

Does that bring any other ideas up?

Skip

don't overlook the exhaust leak on the factory 4.0L manifold. i remember a couple years ago i worked with a couple mechanics that swore high and holly that it was lifter tick or something else. i found the common crack in the manifold and replaced it. guess what......no more tick. oh and my cherokee does it to. not that i care. my engines die because of my driving, not of old age.

Duh - I missed that...

I'm still going to lean toward a tappet knock - thicker oil may help that - but if the intake hole in the side of the thing is plugged, it won't.

The oil hole in the side is rather small, so it can get plugged up easily. I pulled twelve lifters out of my 89 Limited, and found ten of them clogged up with paraffin (it lived on Pennzoil before I got it, apparently.)

The oil pump drive is right under the distributor - so if anything is loose in there, you'll hear it midway down the passenger side of the block. The only thing I can think of that would tick at the rear of the engine would be the lifters for cylinder #6.

And, pulling the valve cover isn't the problem. I'm not overly fond of the fact that AMC didn't design the 242 so you could remove the lifters without pulling the head, but they did - so you'll need everything from the head gasket on up to do the job. When you're going to buy parts for the job, note whether the cylinder head screws have paint marks on the heads - if they do, get new ones. If you aren't sure, get new ones. The 242 cylinder head screws are only good for two torque cycles - then they must be replaced! Check around, you should be able to find sets fairly cheaply. ($50 or so.)

Mine has 275K on it and when I got it, it had 225K on it. Yes mine is VERY noisy. But mine does it cold. Once it gets nice and warmed up (the oil not just the water temp). It is quiet as a brand new motor. I believe it is piston slap. It has had something that sounds like a lifter happen now and then. If I turn the motor off and restart it the sound goes away! Who knows?

Like I said, the noise I get cold is probably piston slap. I did have a mechanic tell me that it was caused by worn wrist pins. How he can tell that noise apart from piston slap...is beyond me.

High Mileage 4.0 = piston slap. That's all I know. Hope it helps a little.

p.s. Hey, if an injector is bad how can you tell? I had a ford HO and the computer codes would tell you. What about an XJ?

My 88 xj, with 235k, does pretty much the same thing. Once it's warm, it's rather quiet.

STP, geeze, if you have a slightly plugged lifter or two STP is not what you want to use on it, you need a detergent, short term would be an engine cleaner you dump in about 20 min before an oil change, longer term would be run a full synthetic oil, that will also clean things up inside a bit more gradually.

Since 4.0 liters are noisy by nature, diagnosing by ear is guess work.
Sounds reflect and conduct all over the place in a motor. But you can put your money on a compression gauge reading. do a compression test, and watch the psi leakdown. If all the cylinders are within spec, feed her the usual oil, and let her tick away. Tappet noise is nonlethal.

(My 92's engine had a tick recently which sounded like a bad lifter. It was a cracked piston skirt. Needless to say, it was low on the compression check.)

Professor Bobo said:

Mine has 275K on it and when I got it, it had 225K on it. Yes mine is VERY noisy. But mine does it cold. Once it gets nice and warmed up (the oil not just the water temp). It is quiet as a brand new motor. I believe it is piston slap. It has had something that sounds like a lifter happen now and then. If I turn the motor off and restart it the sound goes away! Who knows?

Like I said, the noise I get cold is probably piston slap. I did have a mechanic tell me that it was caused by worn wrist pins. How he can tell that noise apart from piston slap...is beyond me.

High Mileage 4.0 = piston slap. That's all I know. Hope it helps a little.

p.s. Hey, if an injector is bad how can you tell? I had a ford HO and the computer codes would tell you. What about an XJ?

Click to expand...

I doubt it's a wrist pin, especially if it goes away or gets quieter when hot and doesn't knock under load. A wrist pin might possibly get quieter with heat, if it's a loose fit in the piston rather than on the rod, but it still should otherwise behave like any bearing-related knock, changing with load and quieting if you kill the ignition on the cylinder. "Might be a wrist pin" is, I suspect, a mechanic's code for "I don't know what the * it is, but I've got a boat payment coming up, so let's tear down the engine."

Location of sounds can be deceptive, though, and one sound that can blend with piston slap is a bad water pump, so I wouldn't forget to check that.

Bad injector indicators will vary with what's wrong and what year you have. No XJ diagnostic system will inform you of clogging, flow and pattern problems in an injector, unless it's so bad that it causes a 96-up OBDII system to diagnose misfire (which it does indirectly by checking crank pulses for regularity). An electrical problem will show as a code in OBD I and II, but it's still then up to you to find whether the problem is in the injector or the harness. There are testers made that will do much of this for you, though still not always definitively.

It all seemed to start (or it got bad enough to notice) AFTER I did an engine flush, then I ran Mobil 1 in it and it seemed louder. Quietest yet is Motorcraft part syn 5w30. I'm sorta afraid to do another flush....... although I have always done it periodically. I don't know what this engine has been through and it was my first oil change with it. I also thinned it it with Marvel oil and tried it and it didn't help, so I tried both ways... Been changing the oil and trying things every 50 miles (I'm also having to deal with fixing a leaky pan plug too, so that's part of the oil change schedule until I find a plug and washer that works)

I was hoping no one said cracked or separated piston skirt! That's my biggest worry. However, I did an old-timers test and shorted out each plug with a grounded awl slipped into the boot of each plug one at a time and listened for a change in the sound. With no ignition in the cylinder, if it were a piston problem like a cracked skirt, the sound would change from the radical difference in forces between firing and not.

Well, no change at all in the sound.

I've heard piston slap when cold in other cars, but with the block being iron and the piston aluminum, the piston will expand more than the cylinder, creating a tighter fit when hot. No? This noise is only when hot, not cold.

It also seems to get louder the hotter it runs, or mybe just varies a little bit randomly. You have to be outside with the AC off and near the fender to hear it. (but once you do, you hear it more than you'd like...)

Consider that in the lifter case too... I get no noise when starting cold or running cold, only after it gets up between maybe 120 and 160. By 160, it's there. If lifters, it should at least be there cold. The viscosity of a 5w oil at 70F is much higher than 20w at 200F (Mobil has all the numbers on their site).

I'm just trying to narrow it down...

Also, not to divert the discussion, but IF it were piston slap, how long before metal fatigue would set in and something crack? If it's a cracked skirt, what then?

Skip

now that ive read your posts thoroughly, sounds like a worn rod bearing. How long it has until failure is anyone's guess. It may never break, or it may throw a rod and grenade the block.

if it was a cracked piston, it would run rough or miss when cold. Mine actually ran fine if it managed to fire enough to heat up and close the cracked piston skirt. There were no outward signs like metal filings in the oil, or oil burning, just cold misfire and knocking sounds...the gentle way to go for an old motor.

There's no tune up, magic sauce, or easy way to fix a rod knock. Let's hope I'm wrong, and it's a ticking lifter.

I must have misread the earlier post and thought it got better hot rather than worse. Ok. Not likely piston slap, but a wrist pin or bearing is possible. I think the next step might be to try the standard old-fashioned test of pulling or shorting one plug wire at a time, and listen for a change in the noise. A bearing should quiet down when you stop combustion.

Thanks, but you must've missed the one where I said I shorted each plug and no difference in sound on any of them.

I'm really hoping for the timing chain, especially since it gets longer as it heats up, but not sure why it would sound louder at the rear of the pan a little bit.

Still open to ideas too....

-Skip

Re: for the high milers with a 4.0 - the sound

OK, the sound from this other thread on "ID this sound" is JUST LIKE mine, only much louder!

http://www.andrewedwardsphotography....ck%20knock.MOV

He says his is more middle/front, but mine is more rear. Gotta put your ear down behind the front wheels to really hear it, although if you know it's there, you can hear it fine anywhere. His is way louder.

I scoped it again. Not coming from the timing cover. Equal all over the pan. You can hear everything turning around with the scope, and it sounds sort of hollow and in the distance. You can also hear it (less) on the valve cover, almost all the way around, and a little bit through the exhaust manifold (more faint, like it's picking it up but not the source).

I'm doubting the chain. Any ideas with this info?

Also, if the chain does break in operation, do the valve hit the piston, or does it clear?

-Skip