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Old 10-19-2006, 08:16 PM   #1
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Default P0300 Misfires past 4000 RPM

Welcome!

Yes I have an Impala, but it has the 3800 which you guys are very familiar with.

So I just got my car back from the mechanic with no luck. The symptoms are a generic P0300 misfire code and a knock and metalic sound after 4,000 RPM. It wont shift up there either or go much past 4,000 RPM at all. This happens almost all the time. The mechanic broke down the misfire to cylinders 1 an 5 with 1 misfiring more than 5. He replaced the coil packs, checked the plugs and wires and switched them around to see if the misfires folllowed but stayed on 1 and 5. Idles and drives fine normally.

He also says the compression is fine and the fuel pressure is fine (new fuel filter too).

I had my cat replaced within 2 years or 15K miles ago.

I am thinking of unbolting the cat and just running it around the block to see if this helps. I cant spend anymore with mechanics or shops or throwing parts at it.

Any ideas on this? I think my next step is to try the ignition control module and return it if it doesnt fix this. I also just put a test tank of 93 in to see if it helps. Next steps? Thanks!

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Old 10-19-2006, 09:56 PM   #2
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are your plugs and wires new? if not I'd start by replacing them
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Old 10-19-2006, 10:23 PM   #3
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So, this happens only during heavy accelaration? All other times (idle, crusing, normal starts and stops) it'* fine? As SJC mentioned, if the plugs and wires haven't been replaced lately, that is always a good start. Also, make certain that all of your battery connections are clean and strong. All grounds too. Has there been any other issues with the car lately? Any work done on it? Pull the plugs, and see if they look fouled or wet. Let us know what you find.
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Old 10-19-2006, 11:25 PM   #4
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Thanks for the help!

Yep, the plugs and wires have been replaced within the past few hundered miles (the car isnt driven much) The mechanic checked the plugs and wires of the misfiring cylinders and swapped them around and such to rule them out. They are some wierd blue wires though, not sure about the brand of the plugs. He cleaned the corrosion off the wire ends when he replaced the coils too.

As for the battery, it hasnt even been something I have considered, it is a new battery. I'll d osme checking around though. On my Fords, a high voltage resistance (bad connection) is shown by flickering lights, I guess not neccisarily the case here.

Thanks agian, keep em coming!

*yep, car is 100% nice at all times below 4000rpm. Gas milage sucks though, 16ave, 20 highway.
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Old 10-19-2006, 11:30 PM   #5
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With that lousy of gas mileage, you may wish to add O2 sensor, as well as throttle body, and mass air flow sensor cleaning to the list of things to do.
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Old 10-19-2006, 11:35 PM   #6
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Quote:
Originally Posted by Archon
With that lousy of gas mileage, you may wish to add O2 sensor, as well as throttle body, and mass air flow sensor cleaning to the list of things to do.
I'll clean the MAF saturday, didnt realize these GM'* you could clean like the Fords.

I was planning on doing the O2 sensorto help milage too... until this started happening. Thanks Archon.
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Old 10-19-2006, 11:49 PM   #7
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Glad to help a fellow 3800 owner. FWIW, your post will likely be moved to the "Other 3800 Powered Cars" area by a moderator. Also, too much use of the "F" word (Ford) could get you a jab or two to the ribs.

This article from techinfo may help you out on the cleaning.

http://www.bonnevilleclub.com/forum/...&highlight=maf
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Old 10-20-2006, 12:12 AM   #8
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Quote:
Originally Posted by Archon
Glad to help a fellow 3800 owner. FWIW, your post will likely be moved to the "Other 3800 Powered Cars" area by a moderator. Also, too much use of the "F" word (Ford) could get you a jab or two to the ribs.

This article from techinfo may help you out on the cleaning.

http://www.bonnevilleclub.com/forum/...&highlight=maf
Sounds good! I hadnt noticed the 'others section' Ooops

Sorry for the F word, How about the L word as in 'Lincoln'? http://www.lincolnsonline.com/forum/...poster&t=46592
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Old 10-20-2006, 09:45 PM   #9
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ttt

Bought an ICM to try out and will check the injector wires, plug wire routing, clean MAF, and pull cat tommorow and see what I come up with.
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Old 10-20-2006, 10:20 PM   #10
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OK, let us know how it works out....best of luck with it....and the "L" word might be a little better...but not much.
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