Random misfire code P0300

1999 CHEVROLET SUBURBAN
210,000 MILES • 5.7L • V8 • 4WD • AUTOMATIC
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RASLINMASTER
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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!
Sep 13, 2017 at 10:26 AM
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MHPAUTOS
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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.
Sep 14, 2017 at 5:04 AM
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RASLINMASTER
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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.
Sep 14, 2017 at 1:44 PM
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STRAILER
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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
Sep 15, 2017 at 4:28 PM