Engine knocking noise - suggestions please

[phrenic13]

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.

[scoobytuff]

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.

[phrenic13]

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

[scoobytuff]

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.

[ejs7597]

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.

[scoobytuff]

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=GOOGL...FQrVOAodaCN_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.

[xTHExFISTx]

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.

[ejs7597]

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.

[danols15]

Originally Posted by ejs7597

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?

[phrenic13]

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.

[ejs7597]

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.

[phrenic13]

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)"

[Douglasjeepowner]

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.

[rhandwor]

Originally Posted by Douglasjeepowner

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.

[ducked]

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.