PO301 code, Diagnostic Help Needed - Mercedes-Benz Forum
 
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post #1 of 8 (permalink) Old 07-17-2008, 08:40 PM Thread Starter
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PO301 code, Diagnostic Help Needed

Hello All:

I've replaced the plug, connector, coil and injector on cylinder #1 but I'm stilll getting PO301, misfire on # 1 cylinder. The misfire is very slight and only noticeable at idle. I'm wondering what else could be at fault ?

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post #2 of 8 (permalink) Old 10-23-2008, 05:59 PM
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I have the same problem with my 2003 c230. My car's idling low and it seems to bottom out at times, which leads to roughness and the check engine light comes on. I've changed spark plug seat as per the stealership (fixed for one day) then the plugs. Next is wires and coils I guess!
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post #3 of 8 (permalink) Old 10-24-2008, 04:40 AM
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Check the appropriate CAT converter and O2 sensor...


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post #4 of 8 (permalink) Old 10-24-2008, 04:24 PM
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I had this problem, finally it was the coil that was too tight.Don't overtighten it.
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post #5 of 8 (permalink) Old 10-24-2008, 05:38 PM
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Exclamation New Defective Coil !!!

I would return the coil as defective and get another one that works when tighten to the specified torque. If just tightening the bolt causes pressure on the epoxy resulting in a bad internal connection, then it will eventually fail or cause problems down the road.

Are the coils genuine MBZ or 3rd party source?


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post #6 of 8 (permalink) Old 01-17-2015, 12:11 PM
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Unhappy

2003 230 K I've replaced the plug, connector, coil and injector on cylinder #1 but I'm still getting PO301, misfire on # 1 cylinder. The misfire is very slight and only noticeable at idle. I'm wondering what else could be at fault ?
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post #7 of 8 (permalink) Old 01-17-2015, 03:07 PM
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put the coil. plug, connector and injector in cylinder #2 . if it follows, then move parts back one at a time. If it doesn't follow, then something else is giving the misfire.


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post #8 of 8 (permalink) Old 01-17-2015, 07:13 PM
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Have you done a compression check?

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