Code P0300 and acceleration low

2007 CHEVROLET SUBURBAN
250,000 MILES • 5.3L • V8 • 2WD • AUTOMATIC
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DYLAN KING
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Engine has 140,000 miles after piston rings replaced and both heads done. Spark plugs and wires changed with new GM brand 6,000 miles ago. Now check engine blinks and traction control message pop up. The code P0300 showed up and acceleration is low to none at some point. Timing is getting lower from 15 to 16 degrees to 10 or 9 degrees when try to accelerate fast and cylinders five and seven show the most misfiring. When engine running at park position looks normal and does not show misfiring.
Any advise please?
Jan 28, 2018 at 10:51 PM
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ASEMASTER6371
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Good morning.

The first thing I would do is to check the fuel pressure. The 300 code is common for low fuel pressure causing engine multiple misfires. there is a access port on the fuel rail to check the pressure.

Roy
Jan 29, 2018 at 5:42 AM
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DYLAN KING
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Hi,
thanks for your answer. I did measure and its stay steady with no drops when accelerate rpm and am running on very reach mixture. Checked the manifold and no hesitation on the gauge. I did change the crankshaft sensor, but did not change anything. I ordered a new camshaft sensor to see if will fix it.
Any other suggestions please?
Jan 31, 2018 at 9:55 AM
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ASEMASTER6371
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what was the fuel pressure??

Roy
Jan 31, 2018 at 10:41 AM