Troble shooting PO 300

[A2000SSinJersey]

My 2000 SS is throwing a PO 300 Misfire code after I replaced the Alternator and belt. ??????? Coincidence???? Voltage is good.

I have replaced the plug wires, as it was my next project. Still same problem. Going to get new plugs and fuel filter later.

HP Scanner is showing Cylinder 7 with misfire history, 2000 or so and cylinder 2 a couple of hundred.

In reading my GM shop manual, one of the tests called for is :
Force the fuel system into Open Loop.

Is that the VCM controls Fuel and Spark tab? That has the Closed Loop On and Off control.?

If so, is turning closed loop off accomplish this test?

Any additional help would be appreciated.

Have fun..............Im not.

[rattle]

misfire in #7 usually indicates crap in the fuel rail plugging injector screen.
take a look at your fuel rail, fuel enters the middle which results in the back of the rail acting as a sediment trap (we will see lots more of this now that gm has gone to RETURNLESS fuel systems on everything)

Pull the fuel rail and clean the rail and the injector screens.

[A2000SSinJersey]

Thanks for the info.

Makes sense to me, but a scarey thought, means my fuel filter is not working right.

I will add that to my list of things to try today.

Thanks again and have fun..........