PO300

Tiny
ZAKKATTACK
  • 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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Thursday, August 23rd, 2007 AT 4:31 PM

4 Replies

Tiny
RASMATAZ
  • MEMBER

A random misfire is normally caused by vacuum leaks and bad gas.

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Thursday, August 23rd, 2007 AT 4:45 PM
Tiny
ZAKKATTACK
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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!

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Thursday, August 23rd, 2007 AT 11:26 PM
Tiny
RASMATAZ
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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.

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Friday, August 24th, 2007 AT 4:53 AM
Tiny
RASMATAZ
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Also check the engine coolant temperature and crankshaft sensors

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Saturday, August 25th, 2007 AT 3:26 AM

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