Chickenfloss

I just bought this jeep a few days ago and happy so far, but yesterday it developed a knock. I changed the transmission pan gasket and filter today and while I was under there I looked for anything loose or that may rattle, but didn't see anything. Fearing the worse I took it to a mechanic that told me it was just valve train noise and that for a jeep, mine was quiet haha.

However, my problem only occurs on acceleration and starts getting more audible about 2k RPM. Usually with a lifter it would happen at idle or get better as the engine heats up. Also, it seems really loud to just be valve train. At 2500RPM it sounds like a thrown rod bearing. I have heard these are also bad with piston slap, but is there anyway to diagnose this from other possible problems without tearing into it? The symptom is reproducible in park/neutral and all motor mounts are still strong and motor just hit 130k.

On a probably unrelated note. The engine has never reached above 150ºF on the gauge. I checked the water temperature after driving it about 30 miles with a separate gauge and the one on the dash is almost right on. As a result my heater gets warm, but never hot like I think it should. Shouldn't this thing be running around the 210ºF area or better?

99 Purple XJ

Its most likely the valve train the 4.0 has a noisy valve train and try changing your thermostat it should be running a 195 thermostat in thefe

Chickenfloss

I have owned a Ford probe GT and it had a noisy motor, but this is ridiculous. The exhaust is so loud I almost can't hear my stereo and I can hear the knocking when I am accelerating over the exhaust. Which is fine, I don't mind loud toys I just want it to get me home haha. I've been listening to a bunch of videos with noises on these motors. So far it sounds a lot like piston slap, but since it's only apparent on higher RPM I think it may be rod knock :S

DFlintstone

Check the torque converter bolts? Behind the little dust cover on the front of the bell housing. Also if one of the starter bolts is too long it can make that same racket, as the flex-plate hits/"burnishes" the end of it.

Chickenfloss

I will check that as soon as I can to be sure, but when I rev the motor at the TB it sounds like it's happening closer to the front(radiator side) of the motor, but it's hard to tell exactly where, without a second pair of hands.

Would also like to add the oil pressure never goes below 40 with both dash and mechanical gauge. Usually at 60 until it warms up for a long while and then lowers itself to the 40-45ish area at idle and back at 60 as soon as you touch the throttle. How much of a difference would it be in pressure if a bearing was on it's way out? Questions may sound stupid. I am still a mechanic in training, of the shade-tree variety.

89Laredo

OIl pressure sounds good.
If anything, its piston slap or a bad lifter.
This is what my old one sounded like, general consensus was a bad lifter.

DFlintstone

Assuming it will do it in park, you can shim the throttle a tad and listen around with something like a dowel, or a section of hose to your ear. (dowel needs to be touching). Also once on a Nissan V6 I saw a crank pulley (there on the front side, ), get loose enough to knock like hell. 3/4 socket I think.

Also you can pull plug wires one at a time and maybe learn something.

Chickenfloss

Definitely not flexplate, listened around and if I put something against the head next to the intake on top of the second piston(front to back) it's the strongest, but can't tell if it's coming from the top or the middle so I still haven't written off piston slap :S Any ideas as far as determining piston slap versus lifters?

A different problem, just wondering if anyone has ran across. After putting the tranny pan back on from filter change the dipstick leaks. I replaced the O-ring trying to fix and it's not bent at all and firmly seated and bolted in place like it should be, still leaking however. Any ideas?

DFlintstone

I would think a fault with a piston would quiet down more than a lifter when you unplug the spark, (at the distributor). If you loosen the connection first, then it's easier to remove it while it's running without getting Zapped!

Chickenfloss

I will try once it's daylight outside again and I get some ***** to try it. I touched a plug wire on a gocart right as my dad pulled the rope to start it when I was younger and haven't touched a live wire since. Going to have to find my insulated pliers

DFlintstone

A shop teacher of mine, (Stan Vermiel, yes, coach Dicks' brother), said him and friends would kill 6 cil engines by shorting plugs with their hands! Said a doc said the spark leaves a little pit and peak when it goes through a joint. Just don't flinch and smack your elbow.

Chickenfloss

Wrist pin =( I don't have the money or the location to tear down and fix it. I may just drive it til it dies or gets so bad I can't take it and swap or rebuild. Guess I am taking it easy on the way around town now =(

A local company sells the long blocks for $940 completely rebuilt. Includes everything but intake manifold, exhaust, valve covers, oil pan, and accessories. They do however include all the gaskets you need to swap yours over. Anyone know a better price than that? It's cheaper than what I could rebuild mine for myself after machine work etc.

Chickenfloss

Just an update 1 mechanic said valve noise. Then 2 others after holding it for time to inspect the problem said wrist pin. Well, today I put in some 91 octane, vs normal 87, for giggles and it stopped the knocking. So I guess that cylinder is firing from compression before the spark ignites it. Could this be caused by a weak plug/plug wire/disty cap or rotor even though it's fine with the higher octane?

DFlintstone

I'm not saying nothing about noten...except, if there's something sticking out, standing up...like carbon in the cylinder it can stay "red" hot after the power stroke and pre-ignite the mix on the next compression.....but I'm not say....

BTW...I wonder what's the test for a bad knock sensor?

jcampbell99

I ran some see foam through mine that is knocking. It did quiet it down a bit.