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Misfire OBD-II Codes P030X

 
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  • 1 Post By RCSnyder
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Old 22 Aug 2015, 07:29 pm
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Location: Liberty MO
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Default Misfire OBD-II Codes P030X

I stumbled across something I think worth sharing about this series of error codes; they are NOT generated by failed injector or ignition components.

Before you scream, "Yes, they are," hear me out.

The ECU monitor many things in the engine, and when the crank position sensor detects a unsteady rotation, it attempts to determine which cylinder might be the culprit. The unsteadiness might be caused by any number of things - yes, including injectors, spark plugs, coil packs, etc - but the ECU is actually reporting the stumble and not the source.

This became vitally important to me recently as I was helping a lady with her '08 PT. After testing, and swapping out, all of the possible and expected components, I was at wits end. Stumbling upon a detailed description of the P030X code series, I did something, had I known sooner, that completely changed my diagnosis. I checked the compression.

Although I still had an incomplete diagnosis, I knew that the head was coming off.

Yes, it was a burnt valve on #3 and not the failed plug and wire on #2 or any of the other tested components that I had first suspected.

Hope this helps.

Bob
Liberty MO
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Old 22 Aug 2015, 08:31 pm
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Default Re: Misfire OBD-II Codes P030X

I was curious on what the spark plug gap was on the old spark plugs when you replaced them trying to find out what was causing the misfire?

Did you check to make sure you didn't have an intake manifold gasket leak around cylinder #3 when you first starting having this problem?

Last edited by ptcruisersteve; 22 Aug 2015 at 09:00 pm.
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Old 24 Aug 2015, 02:27 pm
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Default Re: Misfire OBD-II Codes P030X

Among the first things done were replacing plugs and intake 0-ring gaskets. Neither helped, so we kept digging.
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Old 24 Aug 2015, 02:36 pm
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Default Re: Misfire OBD-II Codes P030X

Wow. How many miles were on that PT? And is this a stock engine without modifications? Do you think this was from carbon buildup or just a poor valve seal from the factory?

I am also really surprised this PT was not throwing codes associated with the O2 sensor too.

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Old 24 Aug 2015, 02:44 pm
j0e j0e is offline
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Default Re: Misfire OBD-II Codes P030X

I had this error code on cylinder 1 a week or so ago.
I changed plugs and wires so the "check engine" light is off, but I still see the code if I do the key procedure.
Think I still have an issue?
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Old 24 Aug 2015, 02:52 pm
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Default Re: Misfire OBD-II Codes P030X

Quote:
Originally Posted by j0e View Post
I had this error code on cylinder 1 a week or so ago.
I changed plugs and wires so the "check engine" light is off, but I still see the code if I do the key procedure.
Think I still have an issue?
You need to clear the codes with an OBDII code reader and then see if they come back. If you don't have a reader that will do this, you may be able to get a local parts store to clear you codes with their reader.

PS: You can get a reader for a very low price nowadays. http://www.amazon.com/gp/product/B00...X8WSVCYY9BN8QG
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Old 24 Aug 2015, 03:50 pm
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Default Re: Misfire OBD-II Codes P030X

I don't really want to respond to much there is a lot of missing information mostly more pictures of the top of the pistons and intake and exhaust runners.

And the information posted by Handy_cruiser is pretty spot on! I would also personally check the readiness area of the PCM for status.

I do want to say the P300 DTC are generic engine none specific codes which include anything that may cause incomplete ignition of the intake combustion mixture of fuel and air(intake charge). This would include low compression in a cylinder.
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Old 23 Sep 2015, 09:30 am
j0e j0e is offline
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Default Re: Misfire OBD-II Codes P030X

I ended up clearing the codes back when I saw these responses.
I've had no issues or codes... until today!
Everything "feels" fine, but the check engine light came on.
I'm bringing it to my mechanic next week anyway, so I guess this will be added to the list.
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