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Flashing P0300! Only under load. (FUEL PRESSURE?)

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2014 Sierra 4.3l V6

First time loaded up with a trailer since last fall and I'm experiencing a flashing check engine (p0300) with no hard codes set.

Will flash for 5-30 seconds and turn off.

When its flashing it is definitely low on power and feels sluggish.


Brand new plugs and wires (within a month or so)

New-ish fuel pressure sensor on the fuel line. (Not GM part, cheapo from autozone)

New fuel pump (1.5 years old)(GM Part)


It happens under acceleration. It happened once on the on ramp to the highway, and happened twice pulling away from a stop under decent acceleration.

It also happened once on the highway, torque converter locked, rolling into the throttle.


I did a test with no trailer hooked up, just driving around. Plugged cheapo scan tool in and monitored the fuel pressure.

Cruising on the highway at 60mph my fuel pressure bounces between 37-53psi.

On steady acceleration is see it sometimes dropping as low as 33 psi and hanging out there for a while (maybe 8-10 seconds).

That is on steady acceleration, not just spike the RPMs and the pressure drops as the pump catches up.


Any ideas other than fuel?
Do those fuel pressure numbers seem low or am I stretching it?


As always, Any ideas help!






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You'd need to know the high pressure fuel pressure as well. The low pressure pump is only supplying fuel to the high pressure fuel pump. Both would need to be within the spec. The low side will vary from 30-60psi pretty regularly.


Flashing check engine light should still spit out some sort of information, you'd need a better scan tool to see that data. A live data scan tool that can show each cylinder misfire would be needed with the check engine light starts flashing.

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