P0300B Random Cylinder Misfire... - Chevy Malibu Forum: Chevrolet Malibu Forums
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post #1 of 4 (permalink) Old 08-16-2010, 11:45 PM Thread Starter
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P0300B Random Cylinder Misfire...

I purchased a used 2000 Chevy Malibu back in May from a used dealer and the car drove great. Got it home, hooked it up to the Genisys EVO and no codes, not even in the history. Purchased with 143k miles on it. Three days ago I started having problems starting it. The same evening I had a really rough idle and couldn't keep the car started without revving up the RPMs. When I hooked up the Genisys I get the error code P0300B, Random Cylinder Misfire.

After changing the Spark Plugs and Wires, I still had a hard time keeping it started and the idle was terrible. Changed the EGR Valve, still no change, changed the fuel filter, which needed it badly, no change. Changed the Fuel Pressure Regulator and was able to keep it idled and started but the RPMs would drop and rise without cause. Checked the streaming data and saw I had misfire on cylinders 1 and 4 which just so happen to be on the same ignition coil pack. Changed the coil pack and was able to keep the car started but it still had a rough idle and loss of power when accelerating. I also developed a ticking noise after changing the coil pack. Swapped coil pack from one side to the other to see if I had gotten a bad coil pack, the tick went away, but I still had an issue with cylinders 1 and 4.

I'm at a loss for what else to do. No Injector codes, no specific cylinder codes, nothing more specific than P0300B. I want to also know what the B stands for in the code, maybe it's more specific to my problem than just a general misfire code....

Any help would be appreciated.
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post #2 of 4 (permalink) Old 08-17-2010, 06:19 AM
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Re: P0300B Random Cylinder Misfire...

"P0300B" means random multiple misfire. If you were to post the freeze frame data that go with it, maybe someone on this forum can make sense of it.

About the only thing that made a difference is the fuel pressure regulator and thus I'd suspect a fuel system problem. I suggest checking the fuel pressure and then fuel injectors 1 and 4. Maybe the "ticking noise" was from those fuel injectors running dry (which would be ruined by now).
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post #3 of 4 (permalink) Old 08-17-2010, 08:21 AM
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Re: P0300B Random Cylinder Misfire...

That does sound suspiciously like a fuel injector problem. Try swapping the injectors with ones from good cylinders and see if the missfire moves around.
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post #4 of 4 (permalink) Old 12-08-2010, 03:07 PM
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Re: P0300B Random Cylinder Misfire...

I had the same problem after replacing the intake manifold gasket on my 97 Malibu. Take the ignition control module off (it's located under the coil packs, be careful to keep the plugs accessible!) and take it to AutoZone to have it tested. Mine died and I was getting a random misfire on cylinders 2/5.
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