Mechanics

PO300

1930 Chevrolet Silverado

03 silverado 2wd w/ 5.3 and now has 103k. The spark plugs and wires were changed at 100k. While under heavy load the check engine light starts to flash but doesn't stay on. It does store po300 code. It doesn't feel like it has a miss or any hesitation, it runs like a champ. Any idea or direction would be much appreciated.
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ZAKKATTACK
August 23, 2007.




A random misfire is normally caused by vacuum leaks and bad gas.
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Rasmataz
Aug 23, 2007.
A random misfire is normally caused by vacuum leaks and bad gas.[/Quote]

If there is a vacuum leak wouldn't the idle be a little rough? It's just strange to me that it only flashes when you have the pedal floored. I hooked up my friends genysis scanner this evening and read the misfire counts. #7 was the only one that would spike over 100 counts and I noticed that's when the light flashes. All others stayed at, or very close to zero. I checked the plug and wire. And swapped one at a time with #5 to see if it made a difference. I also did the same with the coils. #7 is stil acting up. Am I even heading in the right direction with this? You guys are awesome!

Tiny
ZAKKATTACK
Aug 23, 2007.
If there is a vacuum leak wouldn't the idle be a little rough? It's just strange to me that it only flashes when you have the pedal floored. I hooked up my friends genysis scanner this evening and read the misfire counts. #7 was the only one that would spike over 100 counts and I noticed that's when the light flashes. All others stayed at, or very close to zero. I checked the plug and wire. And swapped one at a time with #5 to see if it made a difference. I also did the same with the coils. #7 is stil acting up. Am I even heading in the right direction with this? You guys are awesome![/Quote]

If a misfire in a specific cylinder should lead you to check the spark plug, fuel injector and compression.

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure.

Rasmataz
Aug 24, 2007.
Also check the engine coolant temperature and crankshaft sensors

Rasmataz
Aug 25, 2007.

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