LS Spark Advance Graph

Well, I'm still having missing issues with my LS. I moved the coil packs around (and changed the plugs) to see if the problem would follow the packs. It seems like it *might* have as two of the three that OBDII were telling me were missing are, it seems missing again. One of those is in the number one cylinder.

Anyway, I recorded some data during a test drive today. I haven't really spent any time looking at diagnostics but that spark advance (for the 1st cylinder) chart, to me, looks crazy. The car would idle smoothly when the advance would hold steady. Whenever the advance would get "wild" the car would run like crap.

The graph begins at idle. The car then goes up one hill and then down (with the foot off the gas). Then it goes up another hill. You can see that any load causes the timing to get crazy which is when all the missing happens.

I'm curious what trained eyes think of this.

http://12milesout.net/images/ls_missing_20080904.gif

R

I'm trying to understand what you mean about the missing when you type, "were missing are, it seems missing again." Are you saying that the coils that were missing in the original locations are still missing in the "new" locations? Did you move the spark plugs to the same cylinders as the coils? I would have suggested you leave the spark plugs where they were, it's helpful to only introduce one variable at a time during diagnostics.

Was cylinder #1 missing before and still missing now, even with a different spark plug and coil?

-Rod

I had the OBDII telling me that there were missfires recorded on three cylinders. It also gave me the "random missfires" code. I marked the three potentially bad packs and moved them to other locations when I changed the spark plugs to see if the problems would follow the packs. I also checked for oil leaks etc.

Anyway, I haven't really driven the car too much since I did this. The other day I took it out and it was driving poorly again. The check engine light came on and I got the "random missfire" code again along with two cylinder missfire codes.

I will most likely replace some of the packs. I'm more worried however that i've got a vacuum leak which is causing the car to lean out and is giving me the missfires rather then the actual packs being bad.

Anyway, I was curious if the graph I posted showing timing being all over the place indicated some other issue or might be a symptom of a vacuum leak or failing coils.

Ryan

I'm trying to understand what you mean about the missing when you type, "were missing are, it seems missing again." Are you saying that the coils that were missing in the original locations are still missing in the "new" locations? Did you move the spark plugs to the same cylinders as the coils? I would have suggested you leave the spark plugs where they were, it's helpful to only introduce one variable at a time during diagnostics.

Was cylinder #1 missing before and still missing now, even with a different spark plug and coil?

-Rod

I still don't understand if the misfire code you're now getting is for the two cylinders that now have coils installed on them that were also showing the misfires before, in addition to the random misfire code. If so, don't let the spark timing concern you as it could be due to the misfiring coils.

Which engine does your LS have? If the V8, it wouldn't be too difficult to visually inspect the vacuum lines to alleviate that concern. The V6 has a somewhat problematic rubber PCV elbow located below the lower intake manifold which is not fun to get to.

Can your data logger display "freeze frame" data showing various parameters when the codes were set? Also, monitor to the bank 1 sensor 1 and bank 2 sensor 1 oxygen sensor voltages and see if they go rich or lean following a misfire event. That will help you understand if you're looking for a fuel or air misfire issue. Since it's been running poorly for awhile, the long term fuel trims may indicate if it's air or fuel related as well.

-Rod