po300 code and low vacuum

2004 CHEVROLET TAHOE
176,000 MILES • 5.3L • V8 • 4WD • AUTOMATIC
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REDBONE
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I have change spark plugs, checked coils and they are good. also changed wires.I even checked for vacuum leaks and found none.I hooked up the vacuum gauge and it reads 15hg steady.I also found that when under a load the engine is lacking power.Fuel pressure is at 44 psi and it has a new filter and fuel pump.What would cause the lack of power and low vacuum reading?
Dec 27, 2019 at 3:49 PM
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ASEMASTER6371
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Good evening,

I would start with fuel pressure. I have attached the pressures for both engines for you. Your reading is too low for either one indicating a fuel pump issue.

https://www.2carpros.com/articles/engine-has-low-power-output

As far as vacuum, timing is the reason for low vacuum. How old are the timing chain?

Roy
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Dec 27, 2019 at 5:04 PM