Problem with 05 Tahoe 5.3 non flex fuel

[Stam2000]

So recently my truck has a hard time starting and my fuel economy had dropped from 14ish mpg to 8ish mpg. No change in driving habits. Started about a week after having a Magnaflow muffler installed. I have 120k on the truck so started with replacing plugs with AC Delco Platinum's all gapped to .040, MSD 8.5mm wires (Checked ohms on all before installing) and fresh oil. K&N filter recently cleaned. And fuel pump replaced about 2 months ago. Battery is about a year old. Reset computer.

Only code I'm pulling is EVAP low pressure.

Any ideas out there?

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[M1Gunner]

Purge valve... have you tested it?

I would also check fuel pressure Key On Engine Off to see if it holds pressure. If it doesn't you may have a leaking injector or a bad pressure regulator which would cause a hard start condition.

 

[Stam2000]

Purge valve... have you tested it?

I would also check fuel pressure Key On Engine Off to see if it holds pressure. If it doesn't you may have a leaking injector or a bad pressure regulator which would cause a hard start condition.

Purge valve has been replaced but I will check again. Thanks for the fuel pressure idea. Didn't think of it since I just replaced the pump


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[retiredsparky]

Cam or crank sensor getting weak?