How to effectively check for rod knock?
04-01-2014, 08:44 PM
#17
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Year: 1998
Model: Cherokee
Engine: 4.0 i6
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
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
1. Should i worry about the possible lifter/rocker noise? Or even take into consideration? what could I even do about that?
2. I thought it was a vacuum leak too. No power going up hills, even after TV cable adjustment, so I think I should look into that.
I guess I should just stop worrying about it and come to terms with the fact that the 4.0 makes noise. Ill check the flexplate again, but I mean, if it is some sort of deteriorating engine knock, I wont be rebuilding it anyway, Probably just throw in a decent junkyard engine...
Its just that oil pressure man, screaming "RODS!!! RODS!!!" at me everytime I look at it. I think i need to clean out the sending unit elbow like they said to do on CF, and then check with a mechanical gauge.
04-01-2014, 09:58 PM
#18
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Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
See what others think. Sounds similar to mine to me. The other little tick I think I heard wouldn't bother me. Guys have had issues with their rocker pivots. Guess if it get's worse you will know. Glad I just have a lite that only comes on with ign. at 279K, a gauge would probably be telling me something I'd rather not hear! Btw, no Fram filters allowed! Wix or Napa Gold is one good choice.(same).
Then there is this:
Vacuum leaks suck. I go around with short little shots of starting fluid, if you hit one the sound of the engine will change. Small little shots! You don't want that stuff to accumulate. It's a fire hazard, but It evaporates right away. Also with a tube, or a section of hose you can listen for it. Don't forget the lower O rings on the injectors need to seal as well. (uppers would leak fuel).
The manifold bolts have a habit of loosening, especially that rear one. On anything like that you never want to tighten only one. It can warp/bend, even crack things. If I found that any that where easy to reach where loose, I'd pull the air cleaner and tighten them all, starting in the middle and working out towards the ends. I go over about three times. It's a bear of a spot to get a torque wrench on them all. Just don't ape on it. If its firm and not turning, no point in going on to break it, a REAL *****. The rearmost bolt underneath takes a little doing, but it can be done with the right extension. For that very back one by the firewall I use way long extensions (18"), with a swivel at the socket. Anyway, that's a good thing to check on any old Jeep. ALSO, there is a large line coming off the intake, rear of the TB that goes back to the firewall, across, then forward down to the vacuum ball behind your right front bumper. You can pinch that off or unplug it and cap the nipple to test if you have a leak there.
Then there is this:
Vacuum leaks suck. I go around with short little shots of starting fluid, if you hit one the sound of the engine will change. Small little shots! You don't want that stuff to accumulate. It's a fire hazard, but It evaporates right away. Also with a tube, or a section of hose you can listen for it. Don't forget the lower O rings on the injectors need to seal as well. (uppers would leak fuel).
The manifold bolts have a habit of loosening, especially that rear one. On anything like that you never want to tighten only one. It can warp/bend, even crack things. If I found that any that where easy to reach where loose, I'd pull the air cleaner and tighten them all, starting in the middle and working out towards the ends. I go over about three times. It's a bear of a spot to get a torque wrench on them all. Just don't ape on it. If its firm and not turning, no point in going on to break it, a REAL *****. The rearmost bolt underneath takes a little doing, but it can be done with the right extension. For that very back one by the firewall I use way long extensions (18"), with a swivel at the socket. Anyway, that's a good thing to check on any old Jeep. ALSO, there is a large line coming off the intake, rear of the TB that goes back to the firewall, across, then forward down to the vacuum ball behind your right front bumper. You can pinch that off or unplug it and cap the nipple to test if you have a leak there.
Last edited by DFlintstone; 04-01-2014 at 10:02 PM.
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