Code Po300 question
Code Po300 question
i have a 2003 Trailblazer, was running fine , but coding for O2 sensors,, all of a sudden, "check engine light" started flashing when excelerating, had codes checked, only coding Po300 , does run rough now, can feel the misfire any suggestions as to where to start the repair project would be greatly appreciated
Re: Code Po300 question
What engine in this Trailblazer?
4.2 inline 6, or 5.3 V8 ?
4.2 inline 6, or 5.3 V8 ?
- Attachments
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- trailblazer.jpg (11.73 KiB) Viewed 11327 times
Trailblazer P0300 Misfire Repair
If this is the 4.2 L straight six cylinder engine, a very common cause of misfire is a bad ignition coil, and/or spark plug. They usually break down under heavy engine load. Start the truck and put in gear with your foot on the brake very hard, then give the gas pedal a press all away down and let up, then all the way down that let up. You should feel the misfire as you're hitting the gas pedal. This procedure is called a brake torque. This is good for putting a heavy electrical load on the ignition system. If it were fuel injector, this brake torque would not have much effect. To replace ignition call on the straight six engine, you need to remove the aircleaner assembly. You will see the six ignition coils on top of the valve cover. The spark plugs are under those ignition coils. Each coil is held on by a 10 mm bolt.
Re: Code Po300 question
If the misfire and code P0300 is only at idle, then your Trailblazer could also have a bad cylinder head. These had problem of the valve seats getting damaged and causing a misfire at idle only. Carbon gets in the cylinder head valves and beats up the seats so they will not seal. The cylinder runs lean at idle and causes a misfire.
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- 4.2L cylinder head valves.
- 4.2L Valves.jpg (13.08 KiB) Viewed 9960 times
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