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Discussion Starter · #1 ·
Hi Everyone!
My name is Chris from California. I just purchased a new to me 2009 451 Cabriolet, with 71k mi. I bought it knowing it had a misfire, and assumed it needed valves. Much to my surprise the compression was 155+ in all 3.

As for troubleshooting I have moved the coils around to different cylinders, the spark plugs to different cylinders, and the injectors. No matter what I do the issue stays on cylinder number two. I checked the grounds down by the battery and back by the ECU. I ohmed out the wires for coil pack 2 back the ECU and they're all good.

The thing that I find interesting is it will run fine for about a mile or two then it will throw the code and begin misfiring and idling rough. If I turn the car off and restart it it immediately runs well until it happens again after another mile or two. I did let it idle for about 15 minutes issue free, then I went to test drive and it happened again.

I think i want to try and swap the crank position sensor, seems it may be having an issue tracking at higher RPM.

Thoughts?

I appreciate any help on this, it's really got me stumped.
 

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I hate to break it to you but it could be head gasket.
Mine threw a misfire code for the number one cylinder when it was bad.
It also smoked because it was sucking in oil on that cylinder.
When the car detects a misfire it will shut down that cylinder.
 

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Discussion Starter · #3 ·
So it's not smoking, and not using coolant. It's so odd that as soon as it misses, I can shut it down and fire it back up and it's fine for just a bit.
 

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It’s likely not to the threshold for it to fully shut it down but that’s what will happen if it does.
Got a bore scope with a mirror attachment?
You can inspect the valves with it.
There’s a reason it’s throwing the misfire as they don’t just appear.
Mine smoked but never used coolant.
 

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Discussion Starter · #5 ·
I have a regular bore cam, not one with a mirror. I'll get one on the way. I will mention, this morning when it was cold, it was running so smooth and right as the air injection turned off it got a little rougher but not horrible. Drove great for a couple miles and kicked the code.
 

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Discussion Starter · #7 ·
Once it comes in you need to check the valves.
Could be a burnt valve starting but without being able to see inside it’s a shot in the dark.
I would have thought I'd have low compression in that cyl. But I suppose it could be leaking under combustion pressures... I'll report back with the findings.
 

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One question did you do the compression test with a bit of oil in the cylinders?
Also was it hot or cold when done?
Let me know what you find out.
 

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Discussion Starter · #9 ·
I did not perform a wet compression test. I didn't suspect rings. It would be easy to do, I'll add it to the list
 

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2008 451 cabrio with 44,000 miles - used a few months out of the year (Florida)

Had a similar problem - P0302. Put half a can of SeaFoam into the gas and after a couple of days, it did not come back.

Maybe I was lucky and just delayed the inevitable.
 

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It coud be the injector for that cyl cutting out; current runs thru it, bad circuit opens up, cools off quickly and works on restart.
The OBD II system detects misfires on most vehicles by monitoring variations in the speed of the crankshaft through the crankshaft position sensor. ... If this happens on two consecutive trips, the check engine light will be turned on. This misfire could be either spark or fuel.
 

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Hi Chis,

I also have the same issue as you (I'm also in California) and just posted my issue yesterday (under the subject P0301). Did you ever resolve your issue?

Thanks!

Rudy
 

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Discussion Starter · #14 ·
Hi Chis,

I also have the same issue as you (I'm also in California) and just posted my issue yesterday (under the subject P0301). Did you ever resolve your issue?

Thanks!

Rudy
Hi Chis,

I also have the same issue as you (I'm also in California) and just posted my issue yesterday (under the subject P0301). Did you ever resolve your issue?

Thanks!

Rudy
Issue is a burned exhaust valve on CYL2. I have the head on it's way to get rebuilt.
 
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