DTC P0300 Engine Misfire Detected - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-28-2005, 01:03 PM   #1
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Default DTC P0300 Engine Misfire Detected

99 Bonneville SE...

74,000 miles on it.

I just replaced the plugs and wires about 6 months ago. I also replaced the top coil. Plugs I used are BOSCH platinum +4'* and they were pre-gapped.

Is there any reason why these plugs, coils, or wires could have gone bad this quickly?

I had the guys at my local Firestone shop do the fuel injector cleaning and they also cleaned the throttle body. Air Filter was replaced too.

Just did the SeaForm thing last night and it still is running bad.

What should I do next? Should I go ahead and replace the coils, plugs and wires again?
What about the PCV and O2 sensor? Since I didn't get a specific error from the scan tool on the O2 sensor I guess it is ok?

Oh, I also replaced the fuel filter when I replaced the plugs last time. (6 months or so ago.)
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Old 04-28-2005, 01:14 PM   #2
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First of all, seafoam will make the plugs worse.....fouls them, but you have the worst possible plugs in your car imaginable. Our 3800'* hate bosch plugs and O2 sensors. Many premature failures, often as soon as 30 days.

Run NGK or AC Delco plugs (NGK makes the Delco'*). And measure the resistance of each plug wire. Should be an obvious progression of resistance from 1-3-5 and 2-4-6 wires.

So even if your plugs were ok, they should be replaced after Seafoam anyway. Your O2 may have also been fouled. Replace it with an AC Delco ONLY.

Part numbers are in Techinfo (do the front O2 only, not the one behind the catalytic converter) and get the sensor from www.gmpartsdirect.com or www.acdelco.com at about a 40% discount over dealer retail.
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Old 04-28-2005, 01:56 PM   #3
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I cringed reading that post. A nice fresh set of Bosch..

Still shaking over here.
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Old 04-28-2005, 02:18 PM   #4
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I guess the BOSCH plugs are bad for this car after all then huh?

I thought I had read something about them on here after I put them on the last time, but they seemed to be doing ok a the time.

Guess they failed after couple months of use then.

What about the coils? Should I put some MSD puppies on there?
Anyone got a good price on them? Links?

Thanks.
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Old 04-28-2005, 02:20 PM   #5
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When you pull those plugs, look at the center electrodes. Some will be eroded....way down into the insulator, and some of them will be extruded, decreasing your spark gap.

If your coils are good, stick with them, especially if your misfire goes away after the plugs. MSD coils are only mildly 'hotter' than stock, and equal to the 96+ SSEi coils and 97+ GTP coils.

www.jegs.com is where I got mine.
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Old 04-28-2005, 02:22 PM   #6
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Bosch equipment is $hit. It took me a long time to be a believer, too. I'll never ever use Bosch again.

Their wires are crap too. I just took a set of Bosch off my 99. 3 of them broke as I was removing them. They were only on for 50K miles.

As suggested, stay with the Delcs.
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Old 04-28-2005, 03:00 PM   #7
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Agreed, check the plugs first.... Those Bosh plugs may have the electrodes receding into the insulator like Willren said.... May be burnt, the tip may be carbon black... If you have this issue replace all of the plugs... And see if that takes care of the problem...

Also was there just a code 300 alone? Did they use a code reader or scantool where they could watch to see what cylinders were missfiring and when?

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Old 04-28-2005, 06:20 PM   #8
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Scan Tool I believe....

Said random misfires from all or different cylinders.

I'll put some NGK Iridium TR55IX'* in them this Saturday. I'll check the wires too.

Now they say they come pre-gapped, but I think I'll check them too to make sure they are .060? correct?
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Old 04-28-2005, 06:25 PM   #9
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.060" is correct for stock. Can you put your year and model in your signature?
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Old 04-28-2005, 08:34 PM   #10
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Done....

How'* that for a sig?
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