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Old 10-07-2015, 10:33 PM
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new take on the random misfire codes

Hello,
I am back with Shrek my green 1999 ogre of a wj grand cherokee laredo with 4.0.
a couple of things going on.
first I have had rattling noise issues for a while and when I had him at my mechanic for something that i didn't have time to deal with, the mechanic mentioned that the rattling sounded like it could be from timing chain.

second I have also had issues with flashing CEL intermittently for some time. there has been no pattern as to when it happens. the last time, I actually had scanner and hooked it up. it showed p0300 and a couple of other cylinders as well. but.... here's the kicker. there has been no change in performance. Shrek runs like a champ. no mis-fire of any kind..

I had a thought that perhaps someone can give some feed back on.
if the timing chain has slack, could it be causing difference in when the cam and crank sensors are triggering, and then throwing codes of mis fireing?

At one time, I was thinking the flashing CEL was due to bad CATs but now I am questioning it. it is certainly cheaper to replace timing gears and chain than it is to replace the CA emission CATS.

thanks to anyone who has any thoughts.

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Old 10-08-2015, 04:30 AM
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Re: new take on the random misfire codes

The PCM monitors the crank position sensor signal and detects a misfire when there is a certain speed reduction while a cylinder should fire. I doubt that a rattling timing chain has anything to do with this. The chain will be under tension at one side, while a hydraulic tensioner should keep the other side under a certain tension. If the tensioner doesnīt work properly or there is wear on a chain slider, it could cause noises, but it should not cause misfires. If the chain would skip teeth, it will be an other story, but than you would have a very badly running engine or it would not run at all.
I donīt remember the history, but was the crank position sensor replaced with a mopar part?
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Old 10-08-2015, 11:06 AM
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Re: new take on the random misfire codes

This isn't from a jeep but in my wife's Nissan a few years back she had cam sensor codes go off before she needed the timing chain replacement. It had stretched just enough to through things off. If you Jeep is running well, like in medicine observe it but don't fix what isn't broken yet.
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Old 10-08-2015, 03:41 PM
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The crank sensor was replaced 2 years ago after Shrek left me stranded. I had been on a road trip and stopped for lunch. He had been running great but when i came back out from lunch, he wouldn't start. Replaced with autozone part. Runs fine other than flashing CEL from time to time.
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Old 10-08-2015, 04:44 PM
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Re: new take on the random misfire codes

Leave Shrek be. He's an ogre. But start saving just in case that timing chain needs to be replaced. Costly repair.
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Old 10-08-2015, 04:47 PM
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Re: new take on the random misfire codes

Quote:
Originally Posted by champagneinhand View Post
Leave Shrek be. He's an ogre. But start saving just in case that timing chain needs to be replaced. Costly repair.
Save up even more money and drop in a stroker.
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Old 10-08-2015, 09:21 PM
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Re: new take on the random misfire codes

actually, the timing chain with gears and such is less than $60 via rock auto. I am capable of doing the work myself, so not the costliest repair I have made. I also have been looking around and cannot see anything anywhere about a "tensioner". there is only a snubber on one side.

I did a timing belt on a honda civic a couple of years back, THAT job seems like it was way worse than the chain on this 4.0

I did purchase that dongle that Frango mentioned in another thread. I want to be able to easily monitor what is going on when the CEL begins to flash the next time.

As for the noise, when I get a chance (time is in short supply for me right now) I will be using a stethascope to pinpoint where the noise is coming from. The whole timing chain discussion may, in fact, a pointless discussion.
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Old 10-08-2015, 09:31 PM
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new take on the random misfire codes

Thanks for the reply as I may be doing a timing chain in the Spring on a 2005 CR-V. I think the civic shares the same 2.4L. It's definitely doable but labor intensive. Good access to the valve heads and cam shafts are a bonus. Such a headache on a V type motor.
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