Hammering / knocking noise on 4.0L6 '99 Cherokee

Interesting....

The last time I heard those symptoms was on the first start up of a fresh rebuild and we both just about shit ourselves we were so pissed off. We restarted it and no noise or low, then creeping back up. 3rd time knock knock.

Then as we are leaning over to try and listen where it was coming from, I put my hand on the alternator and almost got burned it was so hot. Bingo, the alternator had decided to give up and something inside was slamming around.

We then used an automotive stethoscope to confirm it. Basically a thin metal rod with a clear plastic hose on one end. The hose goes to the ear and you can really trace down a knock with one.

I would be making or using one before spending money. Even your finger touching parts can sometimes nail it.

One other cause of a strange knock is a worn clutch on the rad fan. This can change every start up and usually is temperature dependent as the clutch changes when hot.

With the engine cold and off, I would try moving the rad fan around for play or clicks.

I would then heat it up good and watch when someone shuts down the engine. If the fan keeps spinning after a hot shutdown, the clutch is baked. It should stop almost immediately.

Mike

Robert Goldpalm wrote:

Could the cause of this problem be found within the electronic / contact / sensor input complex?

Today, no noise at all, so far. No noise at cold start, no noise during normal driving conditions with a warm engine. No noise whatsoever.

So, if it would be a purely mechanical problem such as piston slap, hydraulic lifters, or carbon build up, why is there no noise today?

I am living in the tropics (Thailand) with a very high humidity of around 80-90%. Could it be, that somewhere, an electronic contact or a wrong sensor input causes the engine to produce this ticking / knocking sounds sometimes?

Hydraulic lifters can make an intermittent noise such as you describe. This is because the source of the noise is a lifter that has not been filled with oil. This is usually caused by a bad seal or a blockage, but sometimes they pump down over night; sometimes not. Back in previous decades when these things were a relatively new design they would act up when the vehicle needed an oil change. After an oil change, all would be quiet again. Now they are thought to be better designed, but you still get one acting up now and then.

Humidity where you live could contribute to oil contamination and lifter failure, but since you change your oil fairly often (manufacturers recommend

Earle

Did you check your fan clutch?

Mike

Robert Goldpalm wrote:

Approximately 11/10/03 09:04, Mike Romain uttered for posterity:

Does the vibration damper on the 4.0 get loose and sound pretty close to a piston knock? Have had it happen on other engines, dunno if the 4.0 unit can do it. Actually on the other engine it wasn't loose, it had a big crack in it that made the most noise when cold.

Yes, it can go bad, but usually it starts eating the fan belt before it knocks from what I have read.

Mike

---8>> Did you check your fan clutch?

That's my understanding also.

A mechanic down in Biloxi told me this trick. YMMV Take a feel of the rubber spacer in the vibration damper, if it's sticking out or the surfaces aren't even then it is starting to turn loose.

He also mentioned running a razor blade around the face and checking to see if any rubber comes off. Although I just go by feel.

I still think taking a mechanics stethoscope to the engine is the best bet.

First hand observation: right on. If it's gotten to the point of being loose enough to knock you're probably too poor from replacing belts to do anything about it.

A worn out water pump will also do this - but not for long. The other culprit is the power steering pump and that can go on for a while since the big impeller just whops the case. All of these thing produce more of a thumb than a hard knock, tho.

I think your suggestion of a stethascope is the best one - localize the noise then let us all guess.

Thanks for all the input so far.

Checking around with an improvised stethoscope, the noise seems to come from the engine close to cylinder ( 6 ?) , close to the place, where the PCV is located.

Take today's history for example. Started the cold (it's the tropics) engine. No noise at all. Went to the local mall about 3 miles away, and no noise during the drive there. While slowly cruising at about 1,500 rpm through the parking area, the noise (more like a knocking, not a ticking) appeared. During idle, the knocking was still there, then stopped. With the car parked, raving the engine up to about 1,500 to 2000 rpm and letting it slow down to idle again, the symptoms came back during idle for about

I decided to drive strait to the dealer who is only away another few miles. On the way there, no noise at all. At the dealer, only a very slight ticking sound, but no knocking.

Every time I am at the dealer, there is only a ticking, but never a strong knocking. When this metallic knocking sound appears, you can hear it very clearly, even quit far away from the car.

From reading through similar messages, I would say, it sounds perhaps like the "Piston Slap", but since I have a '99 model, this particular problem should not apply to my engine I guess.

Exhaust pipe hitting on something is my next guess.

Or the heat shield on the cat is loose.

Mike

Robert Goldpalm wrote:

Now it's beginning to sound like a bad lifter letting the pushrod get slack in it - notice any roughnes in the engine when it's banging away? Given a little bleed down, the extra spacing will produce a pretty good noise when the pushrod has any substantial air gap between it and the rocker arm. Another oil change might clean this up or trying one change with a heavier weight oil - like going from 10-30 to

Thanks again for all the suggestions.

So far, I have now:

-Drained about one quarter of oil, refilled with ATF and driven the car about 100 miles.

-Made a complete oil & filter (Mopar) change to Valvoline Maxlife

-This is the second day now with a 10W-40 oil fill, and this morning, the engine has made again this distinct noise at cold (82 F) start. The noise did not go away for a few minutes, then resided from a loud metallic tick to a softer, more subdued ticking sound that could be still heard most of the time during driving.

-To accurately describe the sound is not so easy, but I would say, it is similar to a smaller direct injected diesel engine, comming from cylinder 6 or 5.

Does that sound like a lifter noise? If yes, what are the prospects? Can the engine deteriorate more, or is it just an annoyance, one has to get used to?

The dealer where the car was purchased, switched from Chrysler to Land Rover recently, and Jeeps are serviced now by the local Mercedes dealer. There, they have only one mechanic who is responsible for Jeeps, and he admitted, that he actually has never opened a 4.0 L/6 engine before. Now, unlucky me, if the engine really needs replacement lifters, that guy will somehow experiment with my engine for the first time. I can also not sell the car because of the noise it makes. I could just drive until something gives, and that would be it, but perhaps it would be a long way from now.

So, what do you think?