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P0300 Random/Multiple Misfire

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Old 10-05-2011, 12:34 PM   #1
speedyhawk101
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Default P0300 Random/Multiple Misfire

I took My Z06 to LS Fest Last Month and it ran great. When I got home I parked it in the Garage and let it set for a couple weeks. Last Weekend I got it out and put gas in it. Then I took it to the car wash. While in the Car Wash the "check engine" light started flashing and flashed for about 10 seconds (I think). The Light did not stay on and I did not get any codes. On the way home (maybe 3 miles) the car started missing at low RPM. Still no codes.

This morning I thought I'd drive it to work. This time it was missing so bad it would hardly stay running. The check engine light finally came on and the code was: P0300 Random/Multiple Misfire

The plugs are new and the o2 sensors are new.

The Fuel could have water in it??

The car wash has one of those "undercarriage" cycles that you drive over. And I am wondering if the air filter could have been saturated? (I haven't checked that yet) Has the "Flip Tie" mod, so the filter is exposed......

Any Input?
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Old 10-05-2011, 02:09 PM   #2
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Had this last week, #5 wire was loose at the coil.
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Old 10-05-2011, 02:34 PM   #3
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I'll double check all plug wires and coil pack connections tonight.
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Old 10-05-2011, 02:43 PM   #4
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Flashing CEL is most always Random Misfire.
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Old 10-06-2011, 08:38 AM   #5
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Also check the coil pack grounds at the rear of the driver's side head. More than a few times, that bolt has come lose on people here in the forum.
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Old 10-06-2011, 11:53 AM   #6
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with the others. If your plugs and wires are new there's probably a wire that isn't seated properly. Easy to find it a dark garage, you should be able to see it arcing...
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Old 10-06-2011, 12:29 PM   #7
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thanks for the input guys.
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Old 10-06-2011, 12:32 PM   #8
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Quote:
Originally Posted by speedyhawk101 View Post
thanks for the input guys.
If for some reason you can't find it scan your car for codes with an aftermarket scanner (most auto parts stores will do this for free). The on-board scanner on the C5 will not report the specific cylinder(s) that are missing, it will only show P0300, but an aftermarket scanner will. You will see P0301 for cylinder 1 P0302 for cylinder 2 etc.
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Old 10-06-2011, 09:55 PM   #9
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Checked it out today. I can't seem to track it down just yet. It's missing so bad the Idle sounds like a HUUUUUGE Lumpy cam.

I'll see if my buddy can bring his scan tool over tomorrow.
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Old 10-06-2011, 10:58 PM   #10
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I have the same thing happening with a 04.Changed plugs,39 k on them.Ck'd plug wire resistence,all around 0.777.Ck'd grounds on passenger head.Ck'd battery.I'm mis firing on 4&6. It ran fine one day and terrible the next?
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Old 06-23-2013, 10:32 PM   #11
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Were you able to find out what your problem was as I'm kinda having the same problem
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Old 06-24-2013, 12:06 AM   #12
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I'd try pulling the intake and replacing your intake gaskets with new Fel-Pro gaskets MS92438.

Check all your plugs for fouling and clean with brake cleaner.

Check/replace your two upstream O2 sensors (left and right side) if they look carboned up. They cannot be cleaned.


Had similar issues with my 04 5.3 Tahoe. Shaky intermittent idle with random miss code and got smoother with higher RPMs. Leaky passenger intake gaskets caused all 4 plugs on that side to be fouled and carboned up the O2 sensor on that side as well. Replacing the intake gaskets and both upstream O2 sensors, and cleaning the plugs took care of all idle and misfire problems.

The GM gaskets were very squished and very flat compared to the sealing plane of the intake manifold. Fel-pro gaskets seem slightly thicker than OEM GM gaskets, which give a little more insurance on making a good seal.

Last edited by MN-Brent; 06-24-2013 at 12:40 AM.
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Old 06-24-2013, 12:22 AM   #13
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this thread is almost 2 yrs old.
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Old 06-24-2013, 12:52 AM   #14
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Check for High Voltage leakage or a poor connection on the plug or coil tower.

examine the coil/wires and HV system in a dark area and look for sparks!

You could also have a damaged plug ceramic.

BC
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