Hi guys, while I've lurked around a bit over the past few years I've never actually joined until recently.

TLDR; Engine Knock, came when I replaced the starter, need help!

I seem to have a knock coming from under the hood, it's been there for a little over a year. Some background on it; like I said, it started about a year ago, but when it started it only happened when I would turn the AC on causing the Electric Fan to start and I believe the pump to turn on? It never really bothered me as it wasn't very loud and was only audible when stopped with the AC on.

Well recently I was forced to replace my starter, I was told the jeep had a very easily accessible and easy to replace starter. It took me about 3 hours, not exactly an expert here, but I got it done and the car starts like nobody's business now. Well as soon as I replaced the starter the knock was not only there pretty much right after start up and through until I got up to a certain speed, but it was louder and is there even at idle when in P, R, D, 12, 3, essentially all but neutral.

Say I stop at a stoplight and I don't want to annoy myself and others with the knock, I pop it in neutral at the light and its pretty much non existent. I was looking around and decided that it could have something to do with the flex plate, the wrong oil, or since it's a 96' even the build up of crap from low octane fuel.

I tried to remedy 2 of the 3 possible problems, I got the jeep up and removed the inspection plate, checked all 4 bolts, and only one of them was even remotely loose to the point where I could tighten it even a smidge. I also ran it near empty and through in some 91, rather than the usual 85, but to no avail.

I've just recently gotten an oil change and unfortunately I didn't do it myself and I know it wasn't synthetic. I was told that putting in synthetic could possibly dampen the sound a bit more but I'm skeptical.

So, When I was under the car the sound came from near the flex plate area the loudest, and I'm still convinced it has to do with the area.

If you guys could help it would be so appreciated!

Here's some info about the vehicle:
1996 Jeep Cherokee Sport 4x4 4.0L HO I-6

~93000 Mi. on the car overall, but on a rebuilt engine from about 20000 miles
ago

It was sitting in Maine for 2 years or so doing absolutely nothing so it has quite a bit of rust on the rear.

Anyways I have to go to work but I thank you all in advance for any help you can offer, it is appreciated!

Nick

 

it sounds like a crack in the flexplate. if you heard it before, but had a weak starter, now with a new starter and you say it cranks really hard now, maybe all the new power cracked it more. along with knocking while in drive, but stopped putting a load on the motor but going away when in neutral. Im not an expert but thats what i would think if it was mine. its not an easy fix though, and with cracks that i have seen, you only know when you take it out. thats a lot of work if you arent sure.
On a side note, why was the motor rebuilt at 73,000 miles? the 4.0 is known for 200k plus with no issues so it is odd to see it done so early.

 

Hmm, while the flex plate looked pretty solid still, I guess that could be the issue I'll have to take it to a lift when I get the time and drop the transmission.

As for the rebuilt at 73k, sadly I was a young 14 year old and I was given my grandpas jeep with no knowledge of vehicles whatsoever. The car had been sitting in a rust rich environment with very little gas, coolant, and oil in it for about 2 years unused and then was transported out to Colorado. I decided to drive it around my neighborhood not thinking to look at the levels of any of these fluids. Not only did the engine seize from lack of oil and coolant, but there were about 4 gold ball size holes in the block.

It was a sad day and from then on I learned a lot. It's been about 7 years and this isn't my only car, hence only 20k mi. on it so far. I drive it to work 5 days a week about 5 miles one way and I take it on the occasional off roading trip. I love the car and to this day still hate my naive and stupid kid self for ruining such a lovely engine!

Thanks for the input, Nick

BTW, if anyone needs more info to possibly give a more firm diagnosis, please don't hesitate to ask! I took some short video of the sound and flex plate while the engine was on, but being covered in oil I couldn't do it myself so it's somewhat useless except for the audio.

 

ya, mine was in no way a firm diagnosis it is just what seems to go together with the info provided. Its def one of those things that you dont want to drop a tranny on a hunch lol. I just spent about an hour under mine with a mechanics stethoscope trying to find a knock myself