99 Caravan 3.8 loud engine grinding rattling noise near rear oil pan happens w/ac on

[Woll1234]

Guys, well I replaced the tensioner and idler, no change whatsoever.
Next I'll remove the belt entirely and run the car a little bit.

I have a trick for the serpentine installation. Take a 15mm box-end wench, attach the old serpentine belt to the unused end of the wrench (typ. the 13mm end), engage the wrench on the tensioner bolt, then run the old belt so it hangs over the front bumper. Put your right foot in the belt and step on it to hold the tension off the tensioner while you install the belt. To install, use a yard stick to push it down around the various lower pulleys, then attach an elastic bungee cord to provide temporary upward tension (so it doesn't fall off the lower pulleys; attach the bungee hook to the hood latch above your head) while you finish up on the upper pulleys. Ha!

[Woll1234]

Guys, I took it to Cottman trans. and I forced them to take the transmission off. They didn't want to, because, guess what?? the grinding noise stopped!!In place of the grinding noise, the car now bucked and misfired under load and could barely climb a hill. They said it was a fuel control issue and I should take it to a motor mechanic, they said it would be waste of money to take the trans. off it were just a fuel issue.

I pondered that and I drove the car around. Indeed the noise went away, but this horrible misfire which wasn't there before was really bad, then a trouble code popped through the OBDII, finally! At that point the power of the engine dropped off so much I could barely get up to 30mph on level pavement. Code P1391 which is a crankshaft timing sensor failure/anomaly code. Then I knew I was right. Why?

Because the flexplate has slots in it that are read by a hall-effect transducer (the crank sensor) which tells the main computer, the PCM, where the engine crank is. This is compared to the readings from the cam postion sensor. An anomaly will cause a fuel control/ignition problem since the PCM apparently depends on input from those sensors to time the fuel and spark. When it detects a misfire, the offending cylinder is shut down!! This is to protect the catalytic converter.

What happened was the flexplate was cracked, I believed, in an annular fashion right around the flywheel bolts. I hypothesized that it rotated around that crack, and eventually caught tight allowing torque to be transmitted but also causing a gross mistime for the PCM which in turn caused the improper ignition and fuel delivery, and which finally chimed through the OBDII.

Today they removed the transmission and my suspicions were confirmed. It will be reassembled next week and it should be fine.

[earlyrizr]

glad you found the problem.diagnosis is always tricky,we know that there is a problem ,but the shops usually dont think so.frustrating at best.And while it's out you might aswell change any external seals just to be safe

[bonjoey]

the noise started about 2 months back, the van has 41,000 kms on it. and it has the same noise you guys talking about. One time there was a 01-04 GC by my side and heard the same noise my van has. Only happens with a/c on and idling. sometimes it does it too without the a/c but not too loud. van still have warranty on it so i will bring it to the dealer soon.

[KManiac]

Well folks, I finally corrected the rattling problem with my Town & Country. Since I contributed to this thread earlier, I will post my solution here, too.

A guy I know who works at a local, independent auto parts store, got out his stethoscope and started searching under the hood while the van was running, in gear, with the A/C on (of course, I was in the driver's seat). He found the rattle at the serpentine belt tensioner. I promptly bought a new one.

When I attempted to replace this myself, I became very frustrated because I could not see or access the mounting bolt for this part. Mine has All Wheel Drive, so the PTU blocked my view of the bolt from underneath. Not wanting to get in over my head, I took the van to the local Chrysler dealer and paid them to replace it, making sure to get the old one back. The rattle has gone away. I am happy that this problem is solved and it wasn't as severe a problem as it could have been.

I hope this experience will be helpful to someone else out there.

[jgilhuly]

Thanks to KManiac for bumping this thread up. I started a post on what sounds like the same issue and this thread sheds a lot more light on it especially if my first mechanic's word is correct that the knocking persisted with the serp belt off. Based on what I'm reading and what others are telling me, I now doubt that guy's word.

Someone above mentioned twins...mine are about to turn two so I'm more worried about them eating my tools then asking them to deliver them to me so I'm leaving the diagnosis to a second professional opinion. I will post what I find as soon as I get it.

Thanks everybody...

[luanova9]

Hi, I have a 99 Voyager 3.3 148K miles and based on all the posts here sounds like my problem is the flexplate, too. Runs fine, and has that awful rattle usually when engine is cold and AC on. It has been doing this for months -- usually stops once car has been running for a while. So rather than wait for the failure I was just going to have this done -- especially before a big out-of-state road trip with the family!
I recently had the GATES Conversion Kit for the serpentine belt done (an EXCELLENT solution, by the way!) and it was still making the noise for a while after that. The mechanic that did that kit was concerned about the noise and when I told him about this flexplate suggestion he was able to put it up on the rack and confirm the noise was coming from the rear of the engine...
Well, now the noise has stopped!!! But does this mean the problem went away? I see some post from Woll1234 that mentions his stopped too -- of course I don't have the bucking and such, but that might be my lucky coincidence... Just wondered if anyone else had the experience of the noise going away, or advice if I should just proceed to get the flexplate replaced as I had planned. Thanks!

[jgilhuly]

As I posted a while back on another similar thread, my case ('00GC 3.8, 90k) turned out to be the flex plate and it was diagnosed by my mechanic who said he could "see the plate striking the pan" as he turned the crank. I'm quoting him because I honestly don't know the first thing about that end of the drivetrain or how you make such an observation w/o pulling the transmission. I also don't know how he noticed it and a tranny guy didn't, but it turns out he was right. This came after replacing the tensioner, by the way, to no effect. Seems when it's all said and done, if you pull the serp and the noise persists, smart money's on the flex plate.

[jmangrum]

i had the same problem on a 99 caravan at 90,000 miles that only happened with the ac on and when you turned the wheels (put extra torqe on the engine with the ps pump). it turned out to be a cracked flexplate.

[luanova9]

Just an update -- I went ahead and had my mechanic replace the flex-plate. It was confirmed! I wanted to see the old one so I could know what this was all about. It was cracked all around the bolts, in a circular pattern and would have failed soon! Now it runs nice (actually, it always did), quiet and smooth (overall vibration reduced significantly). I was especially perplexed about why it had stopped making the noise about 2 weeks ago... Apparently it had just gotten jammed temporarily in a certain position. So while they had the tranny out they went ahead and replaced the rear seal - an added benefit... The total cost was $425, including tax. The flexplate itself could only be bought at the dealer and was $65. So now I'm ready for the roadtrip...