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Old 02-27-2016, 04:05 PM
Mopar_Mikey Mopar_Mikey is offline
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Join Date: Mar 2008
Location: Parker Colorado
Posts: 1
Default Chrysler 300M Misfire issue

Hey all,
I'm getting a p0303 and car idles rough. This car is a 2001 Chrysler 300m with 185000 miles on it. It's a 3.5l like every other 300m.
Spark is good so I did a compression test and it's giving me good on all but the #3 as listed below:
Cyl 6000' Sea Level
1 135 161
2 130 155
3 60 71 Wet test 70 or 83 at sea level
4 140 167
5 130 155
6 135 161
I'm pretty certain I have a valve issue with the #3. Rings are not suspect to me since the wet test only brought it up about 10PSI. Overall the compression seems good for a car with 185000 on it.
So far I have done combustion chamber cleaning using the methanol/water cleaning, Seafoam, and the Mopar combustion chamber cleaner with no results....I had the stuff in the garage so thought what the heck, before I pull the head I'd try it.

A little background on the car. I bought it 2 years ago and did a bunch of work on it to get it up to my standards and comfort level. Before I had a chance to change the timing belt it snapped and I took a chance and changed it...already had the kit in the garage. Fired right up after that with no missing and ran great for about 12-15000 miles.
About 2 months ago the CEL came son had put most of those miles on it I only drive it maybe 30 miles a month.
I now have to dig into it to get emissions done on it.
Any suggestions?
I do not have a leakdow tester and no auto parts stores seem to rent them anymore.
I have been contemplating doing the rope test to see if I can free the valve. I do have a bottle of Marvels in the garage....just really don't want to have to pull the head! Really hoping it's not a bent valve.
Any help would be appreciated!
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Old 02-28-2016, 08:29 AM
chirorod chirorod is offline
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Join Date: Nov 2007
Location: Florence, MA
Age: 79
Posts: 724

It has a bad valve, maybe both on that hole. There is your miss. Time to pull both heads and have the valves done. 185K is up there on miles. Also, might be time for rings, as compression comes up wet.
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