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Old 12-08-2012, 08:03 PM   #1
dmince
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Code P0300

'02 TB w/ code P0300 / Random misfire. Started the other day when it was very damp out, FWIW. Feels like ur driving on rumble strips during acceleration. Rough idle also. It does not do this continually though as after a while (minute) it clears up and runs smooth for a while then runs rough & light will again for a while. I seafoamed it today since it been about 60k since last seafoam. I thought that might have helped untill I drove about 20 mile and it went rough again. I also cleaned the oil out of the cam sensor elect connector, since that caused rough running before, although it didn't throw that code. It seems to be very intermitant. '02 TB, 185k miles, orig plugs changed at 125k. Is it actually just going in & out of a limp-mode? Thoughts??? O2 since it's random ???

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Old 12-09-2012, 09:59 AM   #2
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Re: Code P0300

Sounds like an ign misfire, bad plug or coil would be the first thing I would look into, anything but AC Plats or Iridiums will not hold up in that engine.
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Old 12-09-2012, 10:40 AM   #3
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Re: Code P0300

I agree...usually injector or secondary ignition.....but when an injector goes it's constant....

Plugs were changed 60 K ago(how long is that time wise?), but how about the cap, rotor and wires?
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Old 12-09-2012, 06:25 PM   #4
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Re: Code P0300

Remember no cap rotor and wires on the 4.2 TB.
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Old 12-09-2012, 08:04 PM   #5
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Re: Code P0300

Pulled the coils and plugs today. No water in the holes just small amount of oil in three. Plugs were all basiclly the same brown. I pulled 1-4 one at a time and put a spare plug in the coil and held to ground, all 4 had spark. With all the plugs dark so far I installed all new plugs. Did not chk the 5&6 coil due to all the plugs looking similar brown. reassembled all and it seems rougher than before. I started it three times and left it run for a short time 3-4 min. the third time it ran smooth for a while. I did pick up one coil on the parts run, I'll try again tomorrow morn swapping out one coil at a time. FWIW, my son had the exact same symptoms on his honda (only after warmed up) and swapped out the O2 & fixed it. ??? Although this started after a rainy night, I'm not sure this is the typical TB wet cowl condition I've been reading about.
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Old 12-09-2012, 08:15 PM   #6
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Re: Code P0300

Probably 3-4 years since last the plug change. Yes, AC #41-103 Iridium used last time and today.
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Old 12-10-2012, 08:20 AM   #7
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Re: Code P0300

What scan tool are you using to get the P0300 code?
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Old 12-10-2012, 08:49 AM   #8
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Re: Code P0300

Actron. Cp9235. Just ur basic scan/reader
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Old 12-10-2012, 09:24 AM   #9
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Re: Code P0300

O2 will not cause a miss, after the ign. is checked test the resistance of the injectors, look for one with a big difference from the others.
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Old 12-10-2012, 12:08 PM   #10
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Re: Code P0300

Max, once again you are on the ball.......I was thinking Blazer, 4.3, not Trail Blazer, 4.2......
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Old 12-10-2012, 03:49 PM   #11
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Re: Code P0300

Quote:
Originally Posted by dmince View Post
Actron. Cp9235. Just ur basic scan/reader
Is that capable of giving you the TRUE code(s) or is it giving you generic OBD II substitutes?
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Old 12-11-2012, 11:01 AM   #12
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Re: Code P0300

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Originally Posted by Schurkey View Post
Is that capable of giving you the TRUE code(s) or is it giving you generic OBD II substitutes?
Just gives code and description
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Old 12-11-2012, 11:02 AM   #13
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Re: Code P0300

Fixed.. bad coil on 5. Smoothed right out.
Thanks for all ur input & help.
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Old 12-11-2012, 11:47 AM   #14
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Re: Code P0300

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Originally Posted by dmince View Post
Fixed.. bad coil on 5. Smoothed right out.
Thanks for all ur input & help.
That's kinda my point. The REAL code delivered by a REAL scan-tool using professional-grade software would have been P0305--misfire on #5 cylinder. You'd have zeroed-in on cylinder #5 immediately.

The generic OBD II code pulled off by a consumer-grade code reader is P0300--"random misfire". You were led to dick with cylinders that had no functional problems--because your code-reader isn't capable of delivering the TRUE code. Your tool lied to you, told you the misfire was "random" when it was specific to #5.

Folks wonder why I crusade against junk consumer-grade code readers. I used the Actron web site search function, the 9235 isn't even listed.
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Old 12-11-2012, 04:23 PM   #15
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Re: Code P0300

Not everybody can afford a Tech II scanner for an occasional car problem. If they could they would probably just take it somewhere to get it fixed. Most of the time scanners just point you in a direction and the technician still has to use his expertise to core down to the exact problem. It may have took him longer but he seems to have a head on his shoulders and perservered to a solution. Way to go dmince!
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