bobsledjeep

Please help me. I have a 97 cherokee with 115k on it. it has the 4.0 i6

There is a light knock coming from the bottom end. It is definitely not a tick, and is definitely a knock, but no where as near loud as the rod knocker videos on the youtube.

I check torque plate bolts already and they all ok. I do not want to messing with the oil pan, so how i can check for the rod knock?

I try to use hose to listen to oil pan and then torque plate spots but i cannot hear good.

People say to me that if you run engine with spark wire unplugged, you will hear no knock if it is rod knock.

My question is, is it bad to run engine with plug unplugged? Do i unplug and plug back in with engine running? or do i unplug the one, then start the engine, listen, then shut off, plug back in, unplug another one, start, etc.?

Isnt it bad to do this to theengine?making it run on less cylinders? Or is this an ok way to check? Please tell me what you know about this.

I am sorry if i am not clear

TwoXJS

That's how I found my rod knock, although I just unplugged injectors. Unplugged one, start, listen and repeat until the knock went away. Turned out to be my #4 knocking. It won't do any damage to run on only five cylinders at a time, but it will run very rough. CEL will come on, but mine went off as soon as I plugged the injectors back in and I haven't had a problem.

JWheeler

Unplug injectors instead if plugs. That way the cylinder doesn't get washed down with fuel.

DFlintstone

You can unplug a plug wire for a few seconds, it's still getting oil. You can loosen them all with it off to cut down on the chance of getten zapped when you lift it off the cap while it's running.

Although I put "Rod Knock" in the title here, can't be, it would have blown years ago. >

rompnXJ

If you still have a catalytic convertor, disconnect injectors one at a time rather than plugs. Raw fuel will melt the catalyst and clog the cats.

Ye Ol' Cherokee

Okay so i did it. I felt guilty doing that to the jeep, not sure why. I guess, causing it to run like crap, and starting and shutting it repeatedly... but whatever...

So the knock remained, throughout each attempt. I think i will try this again tomorrow, but I will run the jeep for a while to really get the engine hot and the oil thin.

2 Questions...

1.) If the knock does not go away with the injectors pulled, does that mean it is NOT rod knock?

2.) Is it bad to do this "Injector pulling method" too much ? Like would it be bad to go through the whole 6 unplug/start/repeat process again tomorrow?

Radi

Is the noise always there, or is it better/worse with the engine hot? Any change under load? Accelerating or decelerating?
Rod knock changes with engine load, often gets louder on deceleration, worse with RPM.
It'd be a pretty uncommon find with the low mileage you have unless the engine was thrashed or poorly maintained. Do you know the history?

A recording would be useful. The 4.0 wasn't a quiet engine even new. There are plenty of noises most would consider "normal" for that motor.


eta: pulling the injector connectors is harmless. You can do it one by one with the motor running. People have driven these things considerable distances back to civilization with a blown cylinder deactivated, lol. You won't hurt it. At worst you'll get a CEL you'll have to reset.

ej's xj

Leave it runnin when You un plug the injectors that way you dont have to keep runnin back and forth, not gonna hurt anything unplugging either wire ir injector, the little bit of fuel from a miss wont hurt the cat unless you're driving in it for awhile

DFlintstone

You guys are probably right. Running a few seconds with no spark would melt the catalyst, clog the cat, rinse the cylinders and ruin everything. What was I thinking, that happens all the time.

Ye Ol' Cherokee

So i did with the engine hot, and running. It was strange...

When i pull the injector at the very rear of the engine (Most close to the windsheild) the knock seem to become louder, but it might just be something other noise.

When i pull the injector clip 2nd from the front, it does not go away, just harder to hear. Not sure if it is because that is the culprit, or if it is because there are other noises when i pull that one.

I filmed videos so you can hear the sound. Once i can get them on youtube, ill connect the links here

Ye Ol' Cherokee

Here are two videos of my knock. My speakers are blown out, so im not sure which ones which, but the one with the REALLY loud knock is from when i pulled the injector in the rear. The other one is the phone right beneath the oil pan/flex plate area...

Please listen to them both and give your input

https://www.youtube.com/watch?v=nQJA...ature=youtu.be

https://www.youtube.com/watch?v=l_aU...ature=youtu.be

Ye Ol' Cherokee

https://www.youtube.com/watch?v=nQJA...ature=youtu.be

DFlintstone

Boy, I gotta say, the main knock sounds the same as mine has been doing since maybe 01. Part of the reason the OP sold it. It just now occurred to me, why couldn't a guy check crank end play right at the damper pulley? Anyway, another time I posted my U tube, a bunch of guys rang in and said theirs sounds similar.

At one point I hear a second, minor...lifter or rocker?

Camera mikes can be fickle, but that loud hiss sure sounds like a vacuum leak. I'll almost never disagree with Radi, but the bad rods I've had hammered like heck accelerating, climbing a grade.

Btw I've been pulling plug wires off the cap to do dynamic compression tests and isolate noises since 1975, with no ill effect. No harm in pulling the injector wire, unless you have stock injectors on an 87-90. (you might start them leaken and go up in flames)

Anyway my .02, that knock is likely OK

freegdr

Ever check flywheel bolts yet ?

freegdr