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Discussion Starter #1
Hi all.
So I have a 2008 3.5 L Dodge avenger with 200000 miles on it. It started misfiring a couple of days ago so I went to AutoZone and had them read the code. Turns out it was a misfire in cylinder #2. Given the weird electrical problems I have had in the past, I went ahead and had them test the battery as well. They told me my battery was bad so I went ahead and replaced that first. I went home and replaced the battery and that seemed to work. I drove about 60 miles the next day in a single trip and didn't drive my car until the next morning. I took it out the next morning and it ran fine for about 15 minutes until I drove it up a very long and somewhat steep hill at about 20 mph. It started misfiring again at that point, fortunately my destination was only a half mile away. I parked it there and didn't try driving it again for about 7 hours. I then had to drive it about 60 miles to get home. I was pretty nervous about this, but when it wasn't misfiring when I started it and I was able to drive it all the way home with no problems. That 60 miles was a mixture of highway, low speed city roads and multiple stops but no significant uphill. I took it for a drive to the gym, then to the grocery store, then when I left the grocery store it started misfiring again. So I decided to change the spark plugs and ignition coils. The spark plugs did seem to be nearing the end of their life and cylinder 2 wasn't the worst spark plug of the bunch, and it didn't seem that they were bad enough to be the culprit. I took my car out for a three mile drive of varying speeds after mods, and it ran the best it has ever ran. I went and got coffee and it was running perfect when I got to the shop. Sure enough though as soon as I started my car, the engine started misfiring again. With exception of the one time it started misfiring while I was going uphill, every time it has misfired had been after I had driven it and then restarted after a short period of time. Based on what I have read, I may need to replace some of the wiring to the ignition coil. The wiring doesn't seem so simple to replace. I can't seem to find any threads or videos on how to do that. If anyone could point me to a good resource i would really appreciate it. Also, Before I continue to waste my time on this does anyone have any other suggestions besides wiring as to why it's misfiring in these circumstances?
 

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You said you had the codes read, what were they? Have you cleaned any of the sensors or throttle body? Try running a can of Seafoam thru the gas tank and see what happens, it may clean out any fuel related problems and possible injector issues. It also cleans out the O2 sensors and the Cat.
 

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Discussion Starter #3
The code was p0302 and it was the only code. I had planned to use seafoam, directions just say your supposed to use on a near empty tank then fill it up. I am hesitant to burn the rest of my gas tank given my engine problems. Though I don't see why I would have to wait for an empty tank to use seafoam. I guess I could pour some of it in and wait for my cat to cool down then take it for a drive and work some through.

Also I ask this out of curiosity. Why would the the fuel injector start to clog or fail in the conditions I described, starting the car after the engine has warmed up from a recent trip?
 

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IMO more likely Carbon build up on the intake valves soaking up injected fuel spray and therefore not entering into the combustion chamber for proper cylinder firing(misfire). Treating the fuel tank (even at 1/2 full) with seafoam and the and then filling the tank(immediately) IS OK to do. Injectors of any make tend to "gum up" with age, and a fuel system treatment will help the condition, along with helping clean the intake valves of the head and thru the rest of the motor.
Note that a fuel system cleaner is NOT a "magic bullet" instant "cure all", but a least expensive start to good preventive maint., and can in some cases correct minor symptoms like you post of here...without going in and replacing expensive parts and the costly labor with it.
P0302 is misfire on #2 cylinder...If not the coil or plug being worn(they can fail at running temp and not when "cold")...then that leaves the same of the possibility of the fuel injector. Sight unseen by we here on a forum, we can only offer suggestions on areas to investigate that relate to information provided by the person seeking help.
 

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Even if you have a half tank pouring in the full can and going for a drive will not hurt the car. You can pour it in even if the car is running and at full operating temp. I quite often run a can thru about every 4th tank and my Pentastar exhaust has no carbon buildup on the exhaust pipes like I see on so many others. I can take my finger to the inside of the tips and it comes out clean. I use it on all my motors. Outboard, lawn mower, snow blower, weed wacker and my chainsaw.
 
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