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'03 Neon P0301 misfire

Model: 03 Neon Fault Code: P0301 Posted: 2007-07-02 11:11

Hello all, Car is '03 Neon 2.0L auto, approx. 83K mi. Problem is a #1cyl misfire at idle. Car runs, accelerates, and shifts fine. I tuned it up (Plugs- Chpamion RC9YC, wires-belden, air filter- napa) and it started missing and threw code P0301. First thing i did was to swap #1 and #4 wires. Same problem. So I swapped plugs #1 and #2. Same problem. Then I replaced the #1 fuel injector. Same problem. So I replaced the coil. You guessed it...same problem. Help! It only misses at idle. The car accelerates, runs and shifts fine. It also gets normal milage on the highway. But when you come to a stop in D or idle in N or P it misses. I'm stumped. Any advice or help would be greatly appreciated. Thanks in advance.

Related fault codes
P0301
Comments (9)
Anonymous 2007-07-02 12:07

compression test?

Anonymous 2007-07-02 12:57

Not yet, its next on my list. I had kind of ruled that out as it was running fine before i tuned it up. I think I'm just afraid of the possible results. I'll post my findings as soon as run the test.

Anonymous 2007-07-30 15:35

Welp, Finally got around to compression testing, and just as I feared... ~130-140 pounds on cyls. 2,3&4. And on number one, 50 pounds. Looks like I've some work ahead of me.

Anonymous 2007-07-30 15:42

Okay before you condemn the engine you say it was running fine prior to the tune-up? Did you recheck the compression gauge in another cylinder to be sure some dirt wasn't lodged in the schraeder valve on the end of the hose? If it ran fine prior to the tune-up And right after it's missing I'd recheck the plug and wire that you installed! Is there a carbon track on the plug? I know that you've switched stuff around and what no but it may be worth another check. If you put oil down the plug hole for the low cylinder and recheck compression does it come up in pressure? You could try removing the plug from that cylinder when it's hot then pour a good combustion chamber cleaner down that hole and let it sit for a few hours, the longer the better then blow all the carbon out of the hole and recheck everything. I've seen quite a few carbnonned up valves on the 2.0 ltrs and 2.4's. Just be sure not to hydro lock the engine if you do try this. Keep me postted Jeff

Anonymous 2007-07-30 17:08

Thanks for the tips. I've never heard of combustion chamber cleaner. Can you recommend one?

Anonymous 2007-07-30 17:51

The dealer has really good stuff but seafoam is another good one!

Anonymous 2007-07-30 17:56

The same seafoam that you put in the tank for the fuel system?

Anonymous 2007-07-31 09:28

Likely the same stuff! I've never used it myself but people rave about it!

Anonymous 2007-08-08 18:37

I rechecked the plug and wire. They're both fine, so I tried the combustion chamber cleaner (seafoam). I ran the engine with the lights and a/c on for ~20 min. until it was nice and warm. Then I pulled the #1 plug and poured the whole can in (~12oz.). Some of it boiled off but there was enough left to fill the plug hole in the valve cover. I waited a day then cranked the engine to clear the cyl, replaced the plug, reconnected the coil and fired it. It seemed a little better, but still missing. So I ran another compression test and its up a little to ~65 pounds(from 50). poop. Another idea struck me: I've heard of people running the seafoam thru the intake with positive results. So I ran some thru the pcv line, but to no avail. So, it looks like I'm going to be pulling a head. At least she has a reliable daily driver(Subaru). Rather than a piece of Dodge. Yeah, I said it. If you can't dodge it, go ram you're head against a wall . Thanks for all your help, though.