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Random Misfire code P0300 help?!!!

 
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Robert
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PostPosted: Thu Jun 13, 2013 2:51 pm    Post subject:  Random Misfire code P0300 help?!!! Reply with quote

I have a 2005 3.4L Impala and im having startup misfire (bogs). Engine light came on recently P0300 Random Misfire. I am hoping it doesnt mean head gasket coolant leak into a cylinder. I recently replaced all the Intake gasket set upper and lower kit, freeze plugs have been all replaced along with new radiator and hoses due to a separate overheating problem here in HOT Phoenix AZ. Back to misfiring ive replaced new AC Delco Plugs and Wires but still starts up "bogging" momentarly and then clears out after few minutes idling and drives perfectly (even took to Long Beach no prob). Can anyone help!!!!

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Redshiba
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PostPosted: Fri Jun 14, 2013 11:00 am    Post subject:   Reply with quote

Injector maybe?
I had one on a 3.1L motor that did this sort of thing. One injector was the problem.
Just a thought.

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98ss
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PostPosted: Sat Jun 15, 2013 10:56 am    Post subject:   Reply with quote

Normally, we would need to determine if the car was in open loop or closed loop. I think its safe to say open loop. Which is good because it eliminates the oxygen sensors. Since it drives good when the car is hot, I think we could also eliminate the camshaft/crank sensor, coil packs and the ignition module as those usually flake out when hot. The two items that would more likely be suspects are the egr valve, and as said by Redshiba, the injectors, maf sensor, or may also be related by a flaky IAC valve, but that wouldn't set the P0300.

To check the egr, you need to pull it off. 1 electrical connector and 3 10 mm bolts. With the egr off, there will be a piston that should move freely in the center, if it does not clean it out with some carb cleaner. Normally, when they hang up they set an egr "flow" code.

The injectors are actually really easy to check. On the back side of the motor there is a connector up near the alternator. That is the injector harness. There should be 12 pins, 2 for each injector. It might take a couple of trys with the multimeter to figure out which pins go where, but it will be oblivious when the meter shows resistance. Normal injectors are between 12-16 ohms, so like if you see one that is 8, that is most likely the culprit. Since you changed the plugs, did you see any plug that was super black and chard? That would point to an injector problem.
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Robert
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PostPosted: Mon Jun 17, 2013 1:35 am    Post subject:   Reply with quote

98ss; i pulled all the plugs and two were reddish pink (maybe dexcool), other was black, one was white n so were rest. Im hoping its a injector, as redshiba pointed out. It shakes at startup pretty bad, but once hot and car has been running it starts up again normal 1/3 of the time. I will try to test injectors and egr valve next and take it from there, thx.

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PostPosted: Tue Jun 18, 2013 6:31 pm    Post subject:   Reply with quote

By any chance did you run a couple of cans of seafoam thru the engine. That can also turn the plugs a red color. If the plug is black...that is the injector I would look at. A light brown is normal.
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Robert
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PostPosted: Wed Jun 19, 2013 9:26 pm    Post subject:   Reply with quote

98ss wrote:
By any chance did you run a couple of cans of seafoam thru the engine. That can also turn the plugs a red color. If the plug is black...that is the injector I would look at. A light brown is normal.
No never done any additive besides Fuel Injector cleaner, but nothing to coolant system.

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PostPosted: Wed Jun 19, 2013 11:07 pm    Post subject:   Reply with quote

I thought about it after I posted and could the red plugs be residual from the intake leaking?
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PostPosted: Fri Jun 21, 2013 12:03 am    Post subject:   Reply with quote

98ss wrote:
I thought about it after I posted and could the red plugs be residual from the intake leaking?
Yes, i think so too. But either way i replaced all 6 new and all new wires, still horrible shaking at start. then clears out after a minute or 2

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PostPosted: Tue Jul 09, 2013 12:36 am    Post subject:  Update!!!! Reply with quote

Turns out problem was bad head gasket. bummer another $200 gasket set but atleast impala is up and running stronger than ever!

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PostPosted: Fri Jul 12, 2013 9:47 pm    Post subject:   Reply with quote

Dude thats a bummer, but atleast the parts are inexpensive and not that difficult to install.
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PostPosted: Tue Aug 06, 2013 7:33 pm    Post subject:   Reply with quote

98ss wrote:
Dude thats a bummer, but atleast the parts are inexpensive and not that difficult to install.


Yes its all worth it in the end, i just cant part with this car!

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