SS showing Misfire....after Alternator swap????

[A 2000 SS in Jersey]

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.

[foff667]

probably just coincidence...i would take a stronger look at cyl 7 to see whats going on...maybe run the cyl balance test. I would try getting the new plugs if your still on the stockers though & hopefully that will fix it...I know mine were down to like a .040 gap by the time i took my stockers out.

[A 2000 SS in Jersey]

probably just coincidence...i would take a stronger look at cyl 7 to see whats going on...maybe run the cyl balance test. I would try getting the new plugs if your still on the stockers though & hopefully that will fix it...I know mine were down to like a .040 gap by the time i took my stockers out.

Thanks.......hmm cyl balance test?.......is that in HP Tuners? Let me look??

God I dont look forward to changing plugs on the Passenger side.........YIKESSSSSSSS:mad:

HAve funnnnnnnnn

[foff667]

duh good excuse to get some LT's on that thing ;)

[A 2000 SS in Jersey]

Oh yeah..............Headers would be nice............:)

Gotta get it running right first huh...............


And learn HP tuners..........much betterer.................:yup:

Tanx again.........

[A 2000 SS in Jersey]

Originally it was showing msifire on 7 and 2. But primarily on 7.

I switched out the plugs and wires on the drivers side for new ones. Saving the passenger side for later, we all know why on an F body.......duh

So now it is showing misfire on 8 and 1..........primarily 8.........?

I have installed a new fuel filter, checked fuel pressure at fuel rail OK.

Listened to the Fuel injectors via a stethescope, they are clicking away.

The only plug that was fouled with fuel was 7 on drivers side anyway.

I am still worried about why this started right after I changed out the alternator CAnt ne coincidence??


HELP...........LOL

[SeVeReDiStOrTiOn]

make sure the spark plug wires that connect on the coils are on all the way...they should click twice...did you gap the plugs? maybe the belt you put on is slipping, temporarly messing up the timing :think: that's weird that the misses were on 7 and 2..then 8 and 1....whats the firing order, anyone know?

[A 2000 SS in Jersey]

Thanks for the sugestion.

As it turns out, it was the plugs. My problem after I replaced plugs was the number one cylinder wire was not seating properly. I finally heard the spark trying to bridge the gap. There is a metallic shroud that gets installed between the plug and the plug wires that was getting in the way. I dont know its purpose. It has a spring that looks like it wraps around the plug body, so maybe its a heat sink or it protects the wire boot from heat?

Any way, without it I could seat the wire properly. No I need to make ut work with the shroud.

I learned a couple of things here.

Trust the HP Tuners scanner software. It is RIGHT.:)
But, I have to learn to interpret the data. Cockpit error will get you everytime.

My Baby is running again...........Yehawwwww..:yay:

Thanks and have fun.