2015 Tahoe P0300 Random Misfire and Stuttering Under Load

Question

My Tahoe started shaking pretty bad when I try to accelerate on the highway. The check engine light is flashing and it feels like it is losing power, especially when going uphill. It idles okay but you can definitely feel a slight vibration that wasn't there before.

Kevin Tran · Accepted Answer

The issue turned out to be a cracked PCV breather tube behind the intake manifold and a failing high-pressure fuel pump (HPFP) that wasn't keeping up with demand. I replaced the HPFP (part number 12658481) and the foam insulator, then cleared the codes. The fuel pressure at the rail is now holding steady at 2,000+ psi under load and all misfires have stopped. Total cost for the pump and gaskets was about $450.

hd_trucker_77 · Answer

With that mileage, look closely at the intake manifold gaskets or the PCV tubing. Spray some brake cleaner around the intake ports while idling to see if the RPMs jump.

Mike Reynolds · Answer

These 5.3 L83 engines are known for injector failures. If you can use a high-end scanner to run a cylinder balance test, you might find one or two injectors are not spraying enough fuel under high pressure.

Rachel Nguyen · Answer

Check your fuel trims with a scan tool. Since you have P0171 and P0174 (lean codes) alongside the P0300, you likely have a vacuum leak or an unmetered air issue rather than an ignition problem.

2015 Tahoe P0300 Random Misfire and Stuttering Under Load

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