1988 XJ Base, 4.0L, AW4, NP231, D35/30, 2 In BB
I have a knock that sounds like its coming from back of the engine. I havent crawled under it to check to see if its coming from the bellhousing, but it sounds like that general area when listening from the top. I've searched many times for: rod knock, lifter noise, rocker noise, pushrod noise, crank bearing knock, wrist pin knock, piston slap, and flexplate cracking/loose tc bolts. After reading all the threads i could find on the above subjects, the closest thing to my problem seems to be flexplate cracking or loose tc bolts. However, none of the threads said anything about a few of the quirks that my particular engine has developed.
About four months ago i was sitting in traffic and i heard this ticking. It sounded just like an old vw diesel. After pulling away from the light I realized it was my XJ. Thinking it was just a little lifter noise, i changed the oil. The noise didn't go away, so i decided to pull the valve cover on the weekend to check things out. I never got the chance, the tick went away before the weekend. For the next couple of weeks it was very intermittent, it would do it for a few minutes once every couple of days. Over time it got more and more common, and finally it became a permanent ticking. About two months ago its slowly starting going from a loud tick to a loud knock, sounds alot like rod knock. Throughout this whole time, it was just a noise. My XJ idled just like it did before the noise. The gas mileage stayed the same, the oil pressure never went down, and the oil from my oil change when this all started is still clean. Thats what makes me think its the flexplate. The engine shows no sign or internal problems other then the noise itself.
But now its gotten worse. As it gets colder (SE Michigan), the knock has changed once again. The knock itself is still there, but it is now accompanied by a metal on metal scraping noise, and a deep rumble underneath the shifter area, but the rumble only shows up at exactly 1000 RPM and at exactly 2000 RPM. When it does this rumble, the whole truck shakes pretty bad. Its very bad when the truck is in gear, but it also does it when its in park or neutral, just not to the same degree. Also, sometimes, usually only when cold, it makes a howling noise. Try to imagine wind noise from a bad dool seal, but the XJ makes this noise at idle, not moving. The noise isnt a consistent frequency, the pitch changes seemingly randomly.
I also think its important to mention that this rumble was always there, but only at idle and it was very faint, barely noticable, and it happened once in a great while. Also it will knock on acceleration all the way up to 1500 RPM, then it stops. Also on decel the knock is very sharp and only betwenn 2000 and 1500 RPM then it stops entirely until idle, then the knock will start again.
Now for the truly bizarre part. Most of the time on cold start (after parked overnight) it will knock right at startup. But once in a while it wont knock for 2 -3 miles, then it starts. Also, once in a great while, it will stop knocking entirely while running. Sometimes a blip of the throttle and it will come back, sometimes it takes a few minutes to come back, and sometimes it doesnt come back until i restart the engine. This happens about once a week.
It runs just fine, thats whats so confusing about this. At any rate, im paranoid that one of these days what ever is making this god awful noise will just fail, stranding me in rush hour traffic. Since the noises started, i only drive to and from work (~10 miles), and always in morning and afternoon rush hour. The last thing i need is for it to fail in traffic, resulting in many angry people and a tow bill. Any help your guys could provide would be greatly appreciated. Anyone in the Rochester Hills, MI area that would be willing to come down and check it out would gladly be compensated (Beer or Cash).
Anyone got any pointers for me?
I have a knock that sounds like its coming from back of the engine. I havent crawled under it to check to see if its coming from the bellhousing, but it sounds like that general area when listening from the top. I've searched many times for: rod knock, lifter noise, rocker noise, pushrod noise, crank bearing knock, wrist pin knock, piston slap, and flexplate cracking/loose tc bolts. After reading all the threads i could find on the above subjects, the closest thing to my problem seems to be flexplate cracking or loose tc bolts. However, none of the threads said anything about a few of the quirks that my particular engine has developed.
About four months ago i was sitting in traffic and i heard this ticking. It sounded just like an old vw diesel. After pulling away from the light I realized it was my XJ. Thinking it was just a little lifter noise, i changed the oil. The noise didn't go away, so i decided to pull the valve cover on the weekend to check things out. I never got the chance, the tick went away before the weekend. For the next couple of weeks it was very intermittent, it would do it for a few minutes once every couple of days. Over time it got more and more common, and finally it became a permanent ticking. About two months ago its slowly starting going from a loud tick to a loud knock, sounds alot like rod knock. Throughout this whole time, it was just a noise. My XJ idled just like it did before the noise. The gas mileage stayed the same, the oil pressure never went down, and the oil from my oil change when this all started is still clean. Thats what makes me think its the flexplate. The engine shows no sign or internal problems other then the noise itself.
But now its gotten worse. As it gets colder (SE Michigan), the knock has changed once again. The knock itself is still there, but it is now accompanied by a metal on metal scraping noise, and a deep rumble underneath the shifter area, but the rumble only shows up at exactly 1000 RPM and at exactly 2000 RPM. When it does this rumble, the whole truck shakes pretty bad. Its very bad when the truck is in gear, but it also does it when its in park or neutral, just not to the same degree. Also, sometimes, usually only when cold, it makes a howling noise. Try to imagine wind noise from a bad dool seal, but the XJ makes this noise at idle, not moving. The noise isnt a consistent frequency, the pitch changes seemingly randomly.
I also think its important to mention that this rumble was always there, but only at idle and it was very faint, barely noticable, and it happened once in a great while. Also it will knock on acceleration all the way up to 1500 RPM, then it stops. Also on decel the knock is very sharp and only betwenn 2000 and 1500 RPM then it stops entirely until idle, then the knock will start again.
Now for the truly bizarre part. Most of the time on cold start (after parked overnight) it will knock right at startup. But once in a while it wont knock for 2 -3 miles, then it starts. Also, once in a great while, it will stop knocking entirely while running. Sometimes a blip of the throttle and it will come back, sometimes it takes a few minutes to come back, and sometimes it doesnt come back until i restart the engine. This happens about once a week.
It runs just fine, thats whats so confusing about this. At any rate, im paranoid that one of these days what ever is making this god awful noise will just fail, stranding me in rush hour traffic. Since the noises started, i only drive to and from work (~10 miles), and always in morning and afternoon rush hour. The last thing i need is for it to fail in traffic, resulting in many angry people and a tow bill. Any help your guys could provide would be greatly appreciated. Anyone in the Rochester Hills, MI area that would be willing to come down and check it out would gladly be compensated (Beer or Cash).
Anyone got any pointers for me?