Engine knocking noise - suggestions please

[EdgarFan659]

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.

[DVSNCYNIKL]

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.

[EdgarFan659]

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).

[Tim Kriehn]

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.

[EdgarFan659]

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.

[Kennedy200]

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.

[CoolBlue87GT]

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

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.

[Polygon]

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.

[CoolBlue87GT]

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.

.

[CoolBlue87GT]

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 !

[SHADETREEJOHN]

Originally Posted by EdgarFan659

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.

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 !
ShadeTreeJohn

[davidparkwalker]

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

[pimp_squeak]

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

[danols15]

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!!

[ejs7597]

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.