Hi,

I have a 2000 Chevy K3500 crew cab with the 5.7 vortec. Since July I've replaced intake gaskets, distributor, water pump, thermostat, and valve cover gaskets, but just recently it started feeling like it had a slight miss to it. Plugged in my scanner and sure enough the misfire counter showed cylinders 3 and 6 were misfiring. Hmm.. check cylinder 3 plug and it looked pretty bad (Electrode worn out). I thought maybe that was my problem, so I swapped cyl 3 spark plug with cyl 1 before I went out and bought a set of plugs, but now my scanner shows missing on cyl 2 and 7 etc. So it's a random + multiple misfire I guess. I tried unplugging MAF and ECT sensor to see if that would help but to no avail. I don't think its vacuum/fuel delivery related because my fuel trims look perfect. I'm wondering if it may be fuel related though, as this truck has expired July 2020 tags on it so I'm wondering if maybe old gas is causing a miss. Where should I start?

 

I would start with measuring fuel pressure and running some injector cleaner.

 

Fuel pressure is 55psi KOEO and 50psi running if my gauge is correct. I think the recommended spec is 55-65psi but I wouldn't think 5lbs would make a huge difference. It doesn't hesitate or anything just doesn't run 100% right. Tried injector cleaner already but didn't make much difference. Tank is at 1/4 and i'm not sure if it's a 25 gallon tank or a 34 gallon but would it be worth siphoning the gas out and putting fresh new gas in it?

 

the old gas could be causing issues. But if it still runs, then I would just finish burning through it and then fill up.