Help! Strange noise

[SACHEROKEE]

Hi Guys,
Im trying to find out what symptoms a cracked flex plate for an XJ will give you?
I get this gut-wrenching noise from the engine when I floor it from standstill, or if im towing, ie under load. The noise then gradually goes away as the revs climb and the speed increases. Also, if I go over some bumpy road and the jeep bounces, the noise is back on every downward movement of the bounce, as if something turning now rubs (its notbthe wheels)A local site suggests flex plate cracked, but thats close to the gearbox isnt it? This noise sounds like its coming further forward in the engine bay. Could it be my engine is tilting more than normal when accelerating or under load? and perhaps my fan is catching somewhere? Ive tried to look for metal marks but I cant find any.
An engine mount maybe? I do have a slight vibration when the jeep idles, and then at about 80km again.....oh and she is only 1" above stock high. The gearbox guys want R4500 just to look, thats not taking fixing into accvount. HELP!!!!
__________________

[4.3LXJ]

The thing I would check is the fan. It might be hitting the shroud. Also a common thing is for the motor mounts to deteriorate allowing the engine to move around and let the fan hit things it shouldn't.

[BlueXJ]

But to answer your question a cracked flexplate sounds like a rod knock to me. Had one on my daughters Jeep but when I pulled the motor to replace it I found a couple of hairline cracks in between the bolts on the flexplate. Changed the flexplate and re-installed the OEM engine and the knock was gone.

Another thing to check is the transmission mount.

[Mudderoy]

Yeah motor mount came to mind when he was describing this. You could also record a video and put it up on youtube. Then post it in a thread here.

[SACHEROKEE]

Originally Posted by BlueXJ

But to answer your question a cracked flexplate sounds like a rod knock to me. Had one on my daughters Jeep but when I pulled the motor to replace it I found a couple of hairline cracks in between the bolts on the flexplate. Changed the flexplate and re-installed the OEM engine and the knock was gone.

Another thing to check is the transmission mount.

Ok, it definately doesnt sound like a knock, it sounds more like something spinning and rubbing/scraping against something else. Ill check the fan again, although I didnt see any new scuff marks on the housing or fan blades, maybe I must paint a ring on the inside of the housing and see if gets scraped off? How do I check the engine ounts? or transmission mounts?

[default83]

noise. what kind? a knock, a squeel, etc...


check the idler pully, and the fan clutch.

also the water pump bearing could be going out, make sure nothing like the battery is rubbing against any belts...

[SACHEROKEE]

Originally Posted by default83

noise. what kind? a knock, a squeel, etc...


check the idler pully, and the fan clutch.

also the water pump bearing could be going out, make sure nothing like the battery is rubbing against any belts...

It only happens if I floor it, or go up a steep incline, or tow, but not if driving normal. It seems to be when the engine is under load. Its a metal on metal grating noise. I will try record it and post it on youtube.

[4.3LXJ]

It could also be the exhaust pipe hitting something due to bad motor mounts.

[SACHEROKEE]

Originally Posted by 4.3LXJ

It could also be the exhaust pipe hitting something due to bad motor mounts.

Its not a knocking noise, its a metal against metal grating noise, I have looked at the exhaust but cant find any tell tale metal scrapes etc.

[default83]

tranny, u joints, rear end? if it only happens when its under heavy load i would look into the drivetrain.

[SACHEROKEE]

Originally Posted by SACHEROKEE

Its not a knocking noise, its a metal against metal grating noise, I have looked at the exhaust but cant find any tell tale metal scrapes etc.

Ok, took a dive undr the jeep, checked out the fan again. This time whilst lying flat on my back, although I still couldnt see any scuff marks, I felt with my fingers along the path of the fan blades, and noticed that there is literally 2mm gap between the fan blade and the fan housing. As I felt along, I noticed the bottom of the fan housing was cracked, in fact, the one side was broken. That and the fact that the fan housing was loose, ie it rattled when pushed gave me hope that I was on the right track. I pulled the bottom bit of the fan housing off by cutting the remaining piece, and what I found was quite surprising. The bottom section of the housing that extends past the radiators fan, is actually quite thick, and not just a rimm like the rest. The fan had cut about 4mm into that housing. So by tilting too far, the fan was being pushed into the bottom part of the housing. It had gotten so hot at some stage that the plastic had been forged, and was rock hard. Anyway after removing the bottom piece of housing, NO MORE NOISE, and my jeep seems to run nicer too, there was always a sec of "lag" in the power, like something was holding her back, but not anymore, now I touch that accelarator and she launches! My guess is that the fan has been binding to the housing for awhile now, and thus posssibly putting the engine under load? I suspect engine mounts for causing the engine to tilt enough to hit the housing, but with a 2mm gap, thats not alot of tilt. Maybe aftermarket fan housing that is just that much too big? It extends about 2" below the radiator?

[Mudderoy]

Originally Posted by SACHEROKEE

Ok, took a dive undr the jeep, checked out the fan again. This time whilst lying flat on my back, although I still couldnt see any scuff marks, I felt with my fingers along the path of the fan blades, and noticed that there is literally 2mm gap between the fan blade and the fan housing. As I felt along, I noticed the bottom of the fan housing was cracked, in fact, the one side was broken. That and the fact that the fan housing was loose, ie it rattled when pushed gave me hope that I was on the right track. I pulled the bottom bit of the fan housing off by cutting the remaining piece, and what I found was quite surprising. The bottom section of the housing that extends past the radiators fan, is actually quite thick, and not just a rimm like the rest. The fan had cut about 4mm into that housing. So by tilting too far, the fan was being pushed into the bottom part of the housing. It had gotten so hot at some stage that the plastic had been forged, and was rock hard. Anyway after removing the bottom piece of housing, NO MORE NOISE, and my jeep seems to run nicer too, there was always a sec of "lag" in the power, like something was holding her back, but not anymore, now I touch that accelarator and she launches! My guess is that the fan has been binding to the housing for awhile now, and thus posssibly putting the engine under load? I suspect engine mounts for causing the engine to tilt enough to hit the housing, but with a 2mm gap, thats not alot of tilt. Maybe aftermarket fan housing that is just that much too big? It extends about 2" below the radiator?

If you are speaking of the mechanical fan, then yes a remote possibility of the cause of your lag, but I still doubt it. Electric fan, then I can't see that being a problem that causes delayed response.

[SACHEROKEE]

Originally Posted by Mudderoy

If you are speaking of the mechanical fan, then yes a remote possibility of the cause of your lag, but I still doubt it. Electric fan, then I can't see that being a problem that causes delayed response.

Yes the mechanical fan, seems the fan has been rubbing permanently against the housing, noticed that when trying feel the gap between the blades and the plastic, found at the bottom there was no gap at all, it was pushed against the plastic, and not a 2mm gap like the top. Which meant any tilt pushed the fan further into the housing.
Could be that the engine was always under load, albeit minimal, or could just be my wishful thinking but either way, im glad I dont have that gut wrenching noise when the fan fins started cutting into the housing and im TRULY happy it isnt a tranny/transfer case issue

[Mudderoy]

Originally Posted by SACHEROKEE

Yes the mechanical fan, seems the fan has been rubbing permanently against the housing, noticed that when trying feel the gap between the blades and the plastic, found at the bottom there was no gap at all, it was pushed against the plastic, and not a 2mm gap like the top. Which meant any tilt pushed the fan further into the housing.
Could be that the engine was always under load, albeit minimal, or could just be my wishful thinking but either way, im glad I dont have that gut wrenching noise when the fan fins started cutting into the housing and im TRULY happy it isnt a tranny/transfer case issue

Yep it's nice that it isn't something major, but you need to find out why it is this way. Could it be that the shroud just isn't installed correctly? Hopefully it isn't an indicator that the motor is at a steep angle. I know my fan is slightly closer at the bottom due to the transfer case drop, or at least I believe that is why.