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  #1  
Old 07-08-2015, 01:32 PM
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HELP! P0300 multi misfire out of nowhere

Jeep has been running fine. Went on vacation for a week and Jeep was parked in garage. Came home drove it around locally to run a few errands and no issues. That night it was parked outside and we had heavy rains. Next day was heading to work and all of the sudden, rough running, missing, backfires, shakey idle with flashing check engine light!

I pulled the codes and got P0300 multiple misfire two times. Nothing else. Took it to a local independent garage and he thinks it might be the spark control module going bad? His suggestion is take it to the dealer. You know that means big $$$!

Is there anything else I can check before I have it towed to the dealer? Could water have gotten in somewhere while it was sitting outside in the rain? It's typically parked outside anyway, only reason it was in the garage was because we were away for the week.

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  #2  
Old 07-08-2015, 05:01 PM
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Re: HELP! P0300 multi misfire out of nowhere

Spark control module? He probably ment the PCM. Did you check under the hood if the PCM maybe took a shower during the heavy rain? Other than that, i would think of the crank sensor.
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  #3  
Old 07-08-2015, 10:17 PM
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Re: HELP! P0300 multi misfire out of nowhere

Quote:
Originally Posted by Frango100 View Post
Spark control module? He probably ment the PCM. Did you check under the hood if the PCM maybe took a shower during the heavy rain? Other than that, i would think of the crank sensor.
Yes, I did pop the hood and look for water infiltration but everything appeared to be dry. I'm having it towed from the local garage to the Jeep dealer tomorrow, but they can't get to it until Monday. I hope it's something simple like a crank sensor and NOT the PCM!
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Old 07-13-2015, 08:07 PM
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Re: HELP! P0300 multi misfire out of nowhere

Well, I've been without my Jeep since last Tuesday when it started acting up. It was towed and dropped at the Jeep dealer Friday. They said they would look at it today but when I called they said they were too busy and would do it tomorrow. Will have to see what tomorrow brings.
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Old 07-14-2015, 02:56 PM
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Re: HELP! P0300 multi misfire out of nowhere

THIS IS REDICULOUS! Jeep dealer just called me to say they don't know what's wrong! Jeez, are you kidding me! Their suggestion is to do a 'tune up' with new plugs and wires (yes, I told him it doesn't have plug wires) for about $400. The plugs are only $85 if I buy locally. He said it's about 2.5hrs labor. Even at $100 per hour it doesn't come up to $400 total.


I don't know what to do at this point. I could do my own plugs for $85, but I have no way to get the damn truck home 27 miles to my house because it's running so rough with multiple misfires. I already had it towed 30mi from my hometown area to the !@#%(%* dealer so they could use their fancy scan tools and experience to fix it.


Sorry for the rant, but I'm kinda pissed right now. Any suggestions?
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Old 07-14-2015, 04:21 PM
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Re: HELP! P0300 multi misfire out of nowhere

I'm having it towed back to my house so I can change plugs and throw a crank sensor on it to see what happens. I get four AAA tows per year, so no towing charges to deal with. Diagnostic fees are adding up though, and still know nothing specific about what's causing the random misfires.
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Old 07-14-2015, 06:32 PM
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Re: HELP! P0300 multi misfire out of nowhere

I would check the PCM connectors for water ingress (removing them to be sure).
After all those days at the dealer, any problem caused by water can be over now. Did the dealer confirm the misfire, or couldn´t they replicate it?
Doesn´t the 5.7 have plug wires for the second set of plugs?
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  #8  
Old 07-14-2015, 10:23 PM
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Re: HELP! P0300 multi misfire out of nowhere

Quote:
Originally Posted by Frango100 View Post
I would check the PCM connectors for water ingress (removing them to be sure).
After all those days at the dealer, any problem caused by water can be over now. Did the dealer confirm the misfire, or couldn´t they replicate it?
Doesn´t the 5.7 have plug wires for the second set of plugs?
I'll pull the pcm connectors and check more closely. Funny thing is I had to move the Jeep out of a parking space to load on the roll-back and again to pull it in the garage and it was running just fine! You might be right about any water issue being over now that it's had time to dry. The night before the problem began, it was raining sideways, very heavy and blowing winds. Maybe some moisture got in somewhere?

I think I'll clear the codes, check the pcm for moisture and try driving it a few miles to see how it runs. If it acts up again, I'll replace the crank sensor cause it's cheap, and then move on to plugs if problem persists. Thanks for all your suggestions.

Oh, the 2005's had the plug wires. my 2007 only has coil on plug modules.
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Old 07-15-2015, 04:03 PM
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Re: HELP! P0300 multi misfire out of nowhere

I inspected area around pcm- no moisture. I disconnected battery, then pulled pcm connectors- no moisture. I checked all grounds that I could find- all were tight. Battery connections are tight. Left battery disconnected for 20 minutes. Buttoned it up and cleared all codes.

Started Jeep and it was running smooth for a few minutes then as engine started to warm, it starts to miss, then getting worse with some popping sounds in exhaust probably from unspent fuel. Check engine light is flashing. I shut if off to pull codes

I pull the following codes:
P0175- bank 2 too rich
P1129- closed loop fueling not achieved bank 2
P0152- oxy sensor circuit high voltage, bank 2, sensor 1

Any ideas or direction? Can't drive it like this.

Oh, the first local garage I took it to pulled all 16 plugs to inspect and said they look good. normal color, no damage, no wear on electrodes. Champion copper core type.
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Old 07-15-2015, 07:47 PM
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Re: HELP! P0300 multi misfire out of nowhere

There is a problem in the bank 2 sensor 1 electrical circuit. (so the upstream sensor). An O2 sensor high voltage means low oxygen levels = rich mixture. If the mixture is really rich, that is the question. It can be that the O2 sensor is seeing a rich mixture (but not a true one) and will downtrim the fuel injection pulse. That can go that far, that you get a too lean mixture, which simply will not ignite. I believe you said you have a scanner? See what the O2 sensor voltage (the 2-1) is and what the STFT for sensor 2-1 is. I bed that the O2 sensor voltage is steady above the 0.8V and the STFT at -20 or even lower. T
If so, then it could mean that the O2 sensor is bad, or there is water in the connector or the wiring is damaged.
Let me hear what you will find.
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  #11  
Old 07-15-2015, 09:08 PM
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Re: HELP! P0300 multi misfire out of nowhere

This is crazy! I bought some Chevron Techron fuel system cleaner and Seafoam to try because in addition to the heavy rain the night before all this crap started, I remembered filling the tank with gas (from 1/8 tank) at a local station I always use. Maybe I got some really bad gas? Why not try some cleaner?

Anyway, I cleared the codes again, started it up and it ran ok for a minute then as the idle came down and temps came up you could hear slight missing. check engine light came on, flashed a few times, then steady. Codes were P0300 and P0151 oxy sensor low voltage this time. I rev'd it a few times and idle smoothed out, missing stopped. So I drove it around the block and it seems better. So I'm thinking, could this be bad gas and I just need to run the cleaner through? I took it out on the open road and ran the crap out of it in lower gears to keep revs up and burn some gas. Did this for about 20 mins, used 1/8 tank up fast, running it hard with no missing or check engine light.

It is idling smooth again, and no issues at present. Tomorrow I'll try driving to work and see what happens. If codes come back I'll use my scanner to check the O2 values and let you know. Thanks for all the help so far.
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Old 07-15-2015, 09:59 PM
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Re: HELP! P0300 multi misfire out of nowhere

Maybe some water went into the tank?
But that it started up normally and only after warming up a bit, still makes me think that it has someting to do with the O2 sensor itself. When you start the engine, it will run in open loop (not using the O2 sensor intput) and only after warming up a bit it will go into closed loop (using the O2 sensor input to trim the fuel injection pulse).
But lets see, maybe after all it was just water, where ever it was.
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