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Random misfire code P0300

Tiny
RASLINMASTER
  • MEMBER
  • 1999 CHEVROLET SUBURBAN
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 210,000 MILES
Was getting a code saying the number five cylinder had a misfire. I chased that problem by installing new plugs, wires, cap, rotor, and new fuel injector to number five cylinder. Now I am getting a random misfire code. The truck barely runs, will backfire when I try to give it gas, and will not go over thirty mph. Could I have a bad distributor, coil, maybe a bad timing chain? Please help!
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Wednesday, September 13th, 2017 AT 10:26 AM

3 Replies

Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Check for vacuum leaks and certainly look into a new coil as well, or see if you can get an oscilloscope test as this will check the ignition voltages to see if there is a problem there first.
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Thursday, September 14th, 2017 AT 5:04 AM
Tiny
RASLINMASTER
  • MEMBER
  • 5 POSTS
How do I rule out a bad time my chain? MAF? It has backfired a few times and once when I went to start it I hear a loud clunk and then try again and it cranks fine.
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Thursday, September 14th, 2017 AT 1:44 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,574 POSTS
It sounds like you may have lost the timing chain. We can confirm by doing a compression test.

Here is a guide to help you get started.

https://www.2carpros.com/articles/how-to-test-engine-compression

You can rent a gauge for free at most auto parts store.

Please let us know what you find.

Cheers, Ken
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Friday, September 15th, 2017 AT 4:28 PM

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