Got an intermittent knock coming from #6 cylinder on a 88 cherokee. Seems to come around during the hot spells out here in the Sierra foothills. Has an AW4 tranny. Not there when at normal operating temperature but one it gets above 215 or so it starts a-knockin. My thinking is that the tranny is getting a bit hot and bringing up the engine temp and then spreads to the #6 cylinder and causes detonation. It's real weird. The vehicle gets real hot going up hills which leads me, again, to believe it's the tranny gettin hot and then, likewise, heating up the rear of the engine causing #6 to detonate. It only knocks at ifdel too which is even weirder.

I need some input on this. Any body got any ideas? I'm gonna put in a tranny cooler later this week and hopefully that squashes it but we'll see.

Help me out here guys and gals.

 

Bump///

 

Nine views and nothing? Cmon...

 

just be paitent...ive never heard of this and I'm on here all the time...give it some more time and I'm sure someone will have some sort of input

 

Is it a knock, or a rattle? Rattle, kind of like a ball bearing in a can, is usually a collapsed lifter. Knock is usually a lot more serious.

 

Definitely more of a knock. Like "tick tick tock tock tick tock tick tick" LOL

What's weird about it is that its totally intermittent. Sometimes it'll barely do it, sometimes a lot, sometimes not at all. And it's only there at idle. Totally disappears above 1000rpm.

I also took thermometer readings at the bell housing when it does it and it's about 220-225 degrees. I have to believe its a spark knock/detonation that occurs at the #6 cylinder because of the heat at the back end. Anyone else have any ideas?

 

Sounds like a lifter. Whats your oil pressure like?
is it super loud?
Mine does that sometimes to but I know it's not gonna break.

 

Yeah, I'd say it's pretty loud. Oil pressure's nice and healthy.

 

If you haven't already done it, check the torque converter bolts as well. I had the same type of sounds coming from mine, only at idle, and I chased it all over and found an online post on the converter bolts. Mine were all loose and one was almost all the way out. Tightened them and no more noise. Just something to think about.

 

I have never hears spark Knock at an idle but I have not heard everything either. lol Can you get a mechanics stethoscope or a piece of tubing and locate the sound more closely? Is it more on the exhaust side or distributor side? If on the exhaust side I have heard small leaks sound just like a lifter.
When it starts knocking at an idle next time get some insulated pliers or plug wire puller and pull the wire off the number 6 plug and see if it stops. If so might be a broken skirt or something like a rod bearing getting sloppy
clint

 

Bump...

 

I like the idea of a lifter getting tired. Heats up then gets lose. IMO

 

In my experience, engine knocks, once you have one, never go away. They either knock or they don't.

If it's pre-ignition, altitude, weak octane gas, weak spark, and lots of other causes possible...but I've never heard one at idle, either.

A stethescope will probably isolate where it is coming from. If youdon't have one, a long-handle screwdriver works pretty well but is not always safe to use. Careful...

 

kinda sounds like a lifter if it knocks at idle(lower oil psi) and goes away at RPM(Higher oil psi). It's collapsing under low psi and then pumping back up