spark cutting out

[minytrker]

I have a 04 silverado stock except for headers. It seemed like it had a little miss to it. I was logging while driving and noticed when it felt like a miss the timing was dropping 10-16deg or so for a split sec. I had the truck in OL when it happened. It does it at part throttle and idle. It doesnt do it everytime a cylinder fires but it does do maybe once every min maybe. Any idea's?

The truck also wont run in CL with the o2's on it will barley run and get missfire codes. The O2 heaters are flagging for both banks. I just put in new O2's and it didnt help.

[Biggsy]

I have a 04 silverado stock except for headers. It seemed like it had a little miss to it. I was logging while driving and noticed when it felt like a miss the timing was dropping 10-16deg or so for a split sec. I had the truck in OL when it happened. It does it at part throttle and idle. It doesnt do it everytime a cylinder fires but it does do maybe once every min maybe. Any idea's?

The truck also wont run in CL with the o2's on it will barley run and get missfire codes. The O2 heaters are flagging for both banks. I just put in new O2's and it didnt help.

Check the leads to your spark plugs, I had a similar problem and it turned out to be a dud lead.

[minytrker]

I just looked Im logging spark advance for #1 cylinder, so would that mean its #1 having the problem or is the scan tool still reading the other cylinders?

[Biggsy]

I just looked Im logging spark advance for #1 cylinder, so would that mean its #1 having the problem or is the scan tool still reading the other cylinders?

No, could be another cylinder. See if you are getting any missfire counts, they are measured per cylinder. Though when I had that prolem, there were no missfire counts yet every so often it felt like a cylinder was dropping.

If a cylinder does not fire, A/F gets affected which can put you on a different map which can change timing. Also, things like stall savers kick in which muck with the overall timing. I would see peaks and troughs of timing every so often on my log chart with no apparant reason.

Check the wiring to the O2's, there could be a melted plug/cable causing a short.

[minytrker]

No missfire's when in OL but if I try to go to CL I will get missfires. The a/f doesnt change when the spark cuts out.