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AutoMD Member

AutoMD ... 12/17/2013

2002 Buick Century Custom 6 Cyl 3.10L

Engine

Car runs rough, has a p0300 engine code. Can someone advise me as to how to proceed testing?

The car seems to run very well when cold, but smells a little like gas. Once it warms up it has a random misfire, and runs really rough at idle. It performs very well at freeway speeds.
the first thing I did was changed the plugs and wires, I also tested the coils for consistent spark with a spark tester.
After that I borrowed a running diagnostic tester from the mechanic at work. It shows the 02 sensor before the cat is reading a little high. book says 500 ish, this one seems to be between 600 and 850. I also encountered random cylinder misfire.
At idle, engine cold, the number 5 cylinder misfired 60 times in 30 seconds. No other misfires reported on scanner.
at freeway speeds, warmed up. No misfires at all
at idle, warmed up. it varies between cylinders 1,2 5, 6. One cylinder will always show a few more misfires than the others, but it is random on which one will misfire most at any moment.
thank you for reading this.

4 Answers


HouseCallAuto

HouseCallAuto 12/17/2013

Is it always #5 cylinder that you can view misfiring when cold or does it change cylinders sometimes?

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AutoMD Member

AutoMD Member 12/17/2013

From morning to morning it has varied. The first cold test was #5 all the time. Then after it warmed up the misfire moved around between the cylinders. this morning it was number one on the cold start that was missing.

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HouseCallAuto

HouseCallAuto 12/17/2013

sometimes the egr valve builds up deposits inside it that do not let the valve close completely and that would give you both a rough idle and P0300 so remove the egr valve and use any piece of thin metal (once I used a piece of a metal can) and temporarily block off the ports by placing the flat metal under the egr and see if the idle smooths out or not after starting it. If it still idles rough after running it and appears unchanged, remove the metal block off plate and re-install the egr.

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AutoMD Member

AutoMD Member 12/18/2013

There may be some problem with your engine. So you can have a look at this ecu tuning site http://www.obd2life.com/ecu-tuning-tool-c-88.html , hope can help.

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