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Greetings,

I want to thank everyone on this site for your advice. I was able to FINALLY chase down my mystery cause of missing in my 2001 3.8L T&C. I am going to list the process in the hope that it helps one other person avoid my agony!!

115,000 miles started missing - oddly at 47mph and ~ 1500rpm only. Only code was P0303 (#3 misfire). I figured out that the entire windshield wiper assembly could be somewhat easily removed allowing access to the back 3 plugs. Replaced w/ champion plugs and new wires and the van ran great (95% better). Every once in a while I'd get a misfire (again at 47mph and 1500rpm only). Over time (6-8 months it got worse).

150,000 miles-ish - same missing returned (47mph and 1500rpm only). Changed only plugs. 80% better. Again only P0303 code.

Fast forward to 190,000 miles - really missing on any light acceleration. Can barely run the odd 47-1500 mark. Thought maybe a throttle positioning sensor might do the trick due to the fact that on light acceleration is when it acted up. Shifting up transmission by pressing accelerator seemed to eliminate most of the missing issues. NO LUCK changing the TPS. NO CHANGE.

Decided to change the plugs again, used Bosch plugs (only plugs the parts store that was open had) . Improved about 50% but got REALLY bad about 1 week later.

THEN I READ ON THIS MOST EXCELLENT FORUM ABOUT THE COMMON WIRING HARNESS MELTING ISSUE... Low and behold mine was melted too though not as bad as some of the pictures I saw on this forum. I taped every wire, then taped the entire bundle, then wrapped in the OEM cover. Missing was much better but NOT gone. So much for my luck of the melted harness fixing everything...

I spent hours on this forum and saw several posts RE: dislike for Bosch plugs in this engine. So - I replaced the two week old plugs with double platinums and put new wires on (after all I already had the windshield wiper console removed...). Suprise, the problem GOT WORSE :angry1: . Now out of shear frustration I changed the coil pack. Just because it is easy and I was out of ideas.

TAAA DAAA! Runs like new!!! For now. Time will tell.

My thoughts: Melted wiring harness started the issues and eventually when bad enough caused the failure of the coil pack. Initially all I was getting was a P0303 and changing the plugs "almost" eliminated the issue. I think that the plug was slow to foul at first and got worse as the harness got worse which eventually cooked the coil.

I would love to hear the thoughts of the experts.

Hope this eventually helps another 3.8L owner.
 

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Well, on my 1999 3.3L Sport I ran Bosch Platinums and they gave me no problems.

I hope in the future I have no problems with my minivan, so that I won't post problem threads. My only problem now is underbody rust.
 

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Definitely not an expert, but one other possibility I can think of is that the coil serving #3 had a minor defect from the get-go, and wasn't generating the required spark at all times. Then, when you replaced the plugs, it had the effect of giving the lesser spark a better path. There are probably other possibilities as well. But, regardless of the real reason, thanks for posting this repair history. There's a good chance that one or more folks having unresolved ignition problems will read it, throw a $50 coil in, and solve their problem :thumb:
 
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