Engine knocking noise - suggestions please

Hello everyone, I need suggestions on the possible culprit of the engine knocking I am experiencing.

Here's the info -
'92 Jeep Cherokee 6cyl, 122000 miles

I've been getting a soft knocking noise for a couple of months now. I only hear it when the jeep is idling and it isn't there if the jeep has just been started after sitting for a couple of hours. However, the knocking usually will appear within the first minute or two of driving from a cold start. If the jeep has only been off for only a couple of minutes and I start it back up, the knocking is there immediately. The jeep also idles kinda rough, more so than when it was younger.

I've run the STP complete fuel system cleaner through - no luck. I did an engine flush and fresh oil change at 121000 miles and added the STP oil addititive (blue bottle) but there was absolutely no change in the level of knocking. I also tried 89 octane gas (since I've heard that has helped some people) but that didn't work either.

Does anyone know what could be going on here? I've had both spark plugs and the timing belt suggested to me from friends, but I wanted to get other opinions from some jeep drivers out there. I want to take a guess and say that it probably isn't a spark plug problem, since the noise isn't always there but only after the engine has had a chance to warm up.

Any suggestions are welcome. I have an appointment at a Jeep dealership/maintenance place next week, but I'd like to be armed with knowledge so nobody tries to swindle me.

I'm going to take a guess here that you may be experiencing a valve problem in the engine. It can make that annoying ping sound.

It might also be that you have water in the gas tank. I suggest some dry gas to solve that.

I can't be sure unless I have the vehicle in front of me to hear exactly where it is coming from.

A ha!

A couple weeks ago, my Jeep started sputtering and hesitating really bad all of the sudden. When I asked a friend about it, he said to try some dry gas to see if maybe I got a bad tank of gas. That didn't do it.

Then another friend who used to work at a garage told me that it could be a bad spark plug. So I went and picked up some new plugs and a wireset, both Bosch, and replaced them in about a half hour. Pretty simple. Boy did those old spark plugs look nasty...

Not only did this stop the hesitation problem, but it also made the knock almost completely inaudible!

Anyway, I'm glad that it was a relatively cheap fix to make. I was starting to worry that my Jeep wasn't going to last me until next summer (buying new car in June).

I have the same problem with my '91, 6-cylinder. Knocking from beneath the engine at idle, after it warms up. I was wondering if anyone else has this problem and what they have done to solve it.

I'd just like to amend my comment regarding the spark plug change and it's impact on the knocking noise. It turns out that the noise still there - knocks after it warms up in idle but is quiet when cold.

Tim has been told (and then informed me) that this could be attributed to "piston slap", where excessive space between the piston and the cylinder wall cause the piston to knock against the sides.

Does anyone have recommendations for proper maintence of an engine exhibiting piston slap? I do 3000 mile oil changes and lately I have added this stuff called Ristine (sp?) Ring Seal which has seemed to make it a little quieter during the first 1500-2000 miles after the oil change. I've tried to research those oil additives like the ring seal, but I can't seem to find anything useful. At this point I'm really willing to try anything to might help.

I'm probably going to sell the Jeep around August, but I'd like to keep it running well until then. So any suggestions are welcome. Thanks.

If the clearance between the piston and cylinder is getting too big, there isn't much you can do. The only fix is a tear down, rebore and new pistons.


My wife's 2000 Cherokee knocks and pings once and a while. I have found that she drives it too easy. All kind of garbage builds up on the valves and it occasionaly needs cleaned out. I have to give it the old fashioned 'Italian Tune Up'. (no offence intended) Baiscaly, all you need is a straight stretch of road with no cops. Make sure the motor is up to its normal operating temp. Come to a complete stop, and then floor it. Don't let up until your over 100 MPH. The cloud of black smoke is amazing. I feel like 007 putting down a smoke trail. Repeat until the motor no longer produces the cloud of black smoke (usualy have to do it twice). The engine no longer pings or knocks, and the gas mileage improves. I know it sounds a bit redneck'ish, but it works. However, I would be a little more delicate on a motor with a few miles on it.

Years ago I had an AMC Hornet with the same engine - 258 ci - 4 liter

It started having that same noise. I tried replacing the lifters, no help.

The noise drove me crazy, I spent all that money, having the shop replace the lifters & push rods, and turned out not being the problem :mad:

It turned out to be one of the rocker arms, where the pivot & arm met, one was scored, making a tapping noise.

I could have saved hundreds of dollars & bought one 8 dollar rocker & pivot .

Hope this might help. Good luck.

Which 6cyl do you guys have? The 2.8L V6 or the 4.0L I6?

You could be throwing your crank. It is the sound of the crank spinning unbalanced. At one point the crank will snap and send a piston trough your engine wall. I had an 85 Jeep with the 2.8L V6 do that. It is simply the result of worn crank bearings. This is what it COULD be, my Jeep made that same knocking noise. To fix it would require a new engine or a complete rebuild. It won't be cheap, but have an experience mechanic check it out. That is just what it sounds like to me. Just be careful because it could throw the rod at anytime especially during high RPMs so you might want to take it easy until you find out for sure.

Double check those rocker arms, on the bottom
and on the pivot. You may find a burr on the arm
or pivot.

It can't be seen with out removing the arm & looking.

Good luck.

.

I'm surprized that nobody said anything about the headers on a straight six.

They were duals all the way. Made by Hooker Headers.

It sounded sweet !

Hello everyone, I need suggestions on the possible culprit of the engine knocking I am experiencing.

Here's the info -
'92 Jeep Cherokee 6cyl, 122000 miles

I've been getting a soft knocking noise for a couple of months now. I only hear it when the jeep is idling and it isn't there if the jeep has just been started after sitting for a couple of hours. However, the knocking usually will appear within the first minute or two of driving from a cold start. If the jeep has only been off for only a couple of minutes and I start it back up, the knocking is there immediately. The jeep also idles kinda rough, more so than when it was younger.

I've run the STP complete fuel system cleaner through - no luck. I did an engine flush and fresh oil change at 121000 miles and added the STP oil addititive (blue bottle) but there was absolutely no change in the level of knocking. I also tried 89 octane gas (since I've heard that has helped some people) but that didn't work either.

Does anyone know what could be going on here? I've had both spark plugs and the timing belt suggested to me from friends, but I wanted to get other opinions from some jeep drivers out there. I want to take a guess and say that it probably isn't a spark plug problem, since the noise isn't always there but only after the engine has had a chance to warm up.

Any suggestions are welcome. I have an appointment at a Jeep dealership/maintenance place next week, but I'd like to be armed with knowledge so nobody tries to swindle me.


:smokin: Hi. I am new to this forum ,but not to automobiles. I was reading the "cry for help" with a knock noise from a Jeep and wanted to make a subtle remark about sparkplugs. For the same reasons that they must be carefuly chosen for each application they also can have devastating results to the engine as they get older or as other parts become old or worn.
An old or fouled plug can have the same effect as one with an improper heat range, thus creating problems. A plug that is fouled by a rich fuel intake will
fail to ignite for proper combustion can allow a sticky black or dark brown film on the pistons, head and valves, resulting in sticky valves or improper seating allowing intake or exhaust bypass, which can cause rough engine operation or lack of power. On the other hand, a plug can indicate what is happening in the respective cylinder and other
engine componants that can be effected by other causes and problems with the engine. In other words, this Jeep could have electrical problems IE; faulty- Knock Sensor, distributor cap/rotor,oxygen sensor,plug wires, or even a dirty air filter, blown head gasket or contaminated fuel can give adverse effect causes via a sparkplug. I know it has been almost a year since you posted this problem, but NOW it has been running long enough, with the new plugs, to pull the plugs and read the signs on them as to what is going on with the engine



If it hasn't been made, I can't fix it :banghead: !
ShadeTreeJohn

My 1995 Grand Cherokee Limited w/ 125,000 miles had the same problem too. A new set of Bosch Plat Plugs, wires, cap and rotor seemed like a minor miracle getting rid of the noises.

Good luck!

DPW

lmao, my dad used to do that old italian tune up thing with our old van...1986 plymouth voyageur 240k on it, 2.2 stick shift XD....good times

Hello

I have a 1990 XJ 4.0 Automatic about 84,000 Miles

I am having the same problem, when I start it in the morning, It sounds great, and when I get to work about 7 miles away, it is knocking. It is louder coming from underneth it seems and when you stand in front of the XJ, It is barely audible.
Any Suggestions are apreciated!!

My 99 Grand Cherokee 4.0 is also having a ticking sound at lower RPM. I have had 3 mechanics look at it, and all agreed that it was lifter noise, so I replaced the lifters, although I didn't see any external wear on the lifters when I pulled them. That didn't help the noise. So I brought it back to the dealer ship and had them look it over again. They all think the noise is in the upper end still. So since my wife works at the dealer ship and we get parts at cost, I decided I would pull the valve cover and replace the push rods, rocker arms, and fulcrums. Guess What! Noise is still there, maybe even slightly louder. To me the noise sounds like it is coming from the back side of the motor. It is louder when sitting in the Jeep, than when right next to the motor. I personally think it is slightly louder from the bottom side of the engine, but all of the mechanics think it is the top side. I also tried thicker oil before changing the lifters, which didn't help. Any suggestions or ideas would be greatly appreciated.

I have something similar. Just bought some spark plugs and I am going to put them in tomorrow. I will let everyone know what happened.

This is a very common jeep issue. Its not really a problem, it doesn't really hurt anything. I have yet to hear a jeep with some miles on it that didn't do this. The 4.0 engines do this for two reasons. Wrist pin clearance and the material the pistons are made of. I have even heard a few low mileage 4.0 liters do this. Mine has done it for the last 75,000 miles, no problems and hasn't got any worse. As for the comment about the 258 engine, it is actually a 4.2 liter and does not really share this problem with the 4.0. A lot of engines with forged pistons do this, its really nothing to worry about but it does sound bad.

thats good to hear, mine only has 64000 miles on it

Yeah, its really nothing to worry about. It's really just a flaw in design of the motor. I would be willing to be that any Jeep you see on the road or a used car lot probably has the same knocking noise. I doubt what you hear now will really ever get worse, the rings will probably wear before anything else happens. The 4.0L is just based on an old design, when you keep adding new technology to an old design you have some minor problems sometimes.

You say it probably won't get worse. I replaced my lifters, push rods, rocker arms, and fulcrums since the mechanics all said it was in the top end. Mine is definatly a little louder now. A lot louder when the engine is cold. I would just drive it, till it died, but it is my wifes vehicle, and she "can't stand the noise". "TURN THE RADIO UP". It wouldn't be so bad if it wasn't louder in the vehicle than ourside. Anyway, it is either fix the noise or sell the Jeep. Since I don't owe anything on the Jeep, if it is the wrist pins, could I pull the oil pan and replace the pistions and rods from the bottom side? Is there room to do that in this motor? The top side of the pistions were all very clean, and there was no scaring on the cylinder walls, on the top side.

They do reach a point where they are damn obnoxious. It's probably won't lay down on you though. You could rebuild the motor, or you could buy a new long block. I know Quadratec has either a stock long block or a stroker motor, pick your poison. Both engines have good warraties on them. On the stock replacement they will pick up the core for you at no charge when you a ready and credit you for it. http://www.quadratec.com/?sgsc=GOOGLEQUADTECH&gclid=CKiuzoj274wCFQrVOAodaCN_DQ. This is the link to Quadratec. There are other places that sell pretty impessive engine packages as well. You could probably fix the noise by rebuilding the motor like you were talking about. I personally wouldn't worry about it, but I know where you are coming from. If mama ain't happy nobody is happy.

Im pretty sure this is no help to anyone...but i had a knocking/ticking noise on my 94 cherokee,and it turned out to be the power steering hose knocking agianst the engine.

Turns out the knocking noise was a crack in piston #6 skirt. It finally started to clunk instead of knock, so I pulled the oil pan to find a big chunk of the piston in the bottom of the pan. So I pulled the head again and pulled out the piston, and found that it didn't damage the cylinder wall somehow, so I honed it out and slapped in a new piston and rod. I have put about 5,000 miles on it since then, and it is running strong and no more knocking noises.
To diagnose the piston noise, I unhooked the power to 1 injector at a time, listening for a change in the noise. When I unhooked injector 6, the engine was much quiter, so I assumed that was the bad piston. Pulled the pan, and that was correct.

To diagnose the piston noise, I unhooked the power to 1 injector at a time, listening for a change in the noise.

This may sound dumb, but I have had no experience in doing anything like this before. is there anything you need to do before you can just disconnect the power to the injector?

hmmmm disconnecting the power to each injector. not a bad idea at all. not sure if i know how to, but i can do some studying and figure it out.

It is simple to unhook the power to the injector. On top of each injector there is a wire connected to it. push the red tab up on the connection, and it will allow you to unhook the connector. Start with piston #1 and work your way back. Listen for a change in the noise after you unplug the injector. Plug it back in and move to pistion #2, keep doing this until you reach the last pistion. In my case, once I reached pistion #6, the sound was dramtically quiter.

after reading this i went to look and was like, "duh". ill try that later, but for now i have a new problem. Check out my new thread "NO START (no bus)"

My 99 Cherokee is doing something similar, starts up great runs normal, drive about 7 miles it starts the knock, and engine spudders, losses acceleration, and a couple of times it's died, when I try to start up again it miss fires, acts like its not getting gas, and runs rough. Let it sit few hours it runs great for about 7-10 miles starts again. Spark plugs? Throttle positioning sensor? I'm lost.

My 99 Cherokee is doing something similar, starts up great runs normal, drive about 7 miles it starts the knock, and engine spudders, losses acceleration, and a couple of times it's died, when I try to start up again it miss fires, acts like its not getting gas, and runs rough. Let it sit few hours it runs great for about 7-10 miles starts again. Spark plugs? Throttle positioning sensor? I'm lost.
I would go To Advanced or Auto Zone and get an oil pressure test gauge. I would make sure you have adequate oil pressure. As the engine gets hot the oil thins and it maybe this causing the knock.
Are you getting any indications of ECM codes. A bad temperature sensor could be preventing it from changing loops.
Check both radiator hoses and make sure both are hot after 7 miles an engine over temperature will knock.
Check for vacuum to the fuel pressure regulator if you get gas in the vacuum line replace.

Could be almost anything with the limited info available, BUT If this was happening to my vehicle I would probably

(a) Try the effect of very thick oil, going for a viscosity improver additive if I was already using something thick like 20W/50 (I actually use a blend of 1:1 15W40 and straight 40)

If this reduces the noise (or makes it start later) its probably excess play (perhaps in the crank or big end bearings).

(b) Try a water decoke. This is fairly tedious to do but I have had it make pre-ignition and run-on problems go away. Similar effect to the "Italian Tune-up", but that might be damaging with engine pre-ignition.

6 year old thread.

6 year old thread.

22 if you count the original post!

Yeah, let's shut this one down.