2007 Corvette Ignition Timing Goes Crazy at WOT

[Andrew Woodward]

I am having a very weird issue with this 07 Corvette, and oddly enough, I tuned another 07 Corvette earlier this week that did the same thing. For context this is an LS3 swapped 07 but that shouldn't have any affect on this issue. LS2 throttle body.

I own my own shop and tune full time so I've tuned a lot of Vettes and other cars and am used to tuning diagnostics but this is new to what I've seen. Basically every time I go WOT on the dyno or the street (including the other 07 I tuned) the ignition timing starts to look like a seismic earthquake chart. I have noticed between both cars the effect is worse at low RPM. The other 07 I just did was a Z06 which did it mainly between 3000 and 3500rpm with some dips in the high rpm area as well but it didn't start until 3000rpm. Both cars are cammed. Keep in mind there is NO KNOCK when this is happening. The first pull I did on this LS3 07 I noticed it again but not as bad as the last Vette I just did. The next pull I just did was way worse than what the other Z06 did and heavily influenced the dyno graph according to the logged ignition timing.

I always setup my tunes to provide timing directly from the base map and never have trouble achieving exactly what I command. This problem however appears to be some sort of interference. My thought is potentially electrical, alternator, or the PCM. My hesitation in condemning the PCM is I would like to see other issues stemming from the computer but this is it.

I'm hoping to find that I'm not the only one who has seen this since I saw no other threads on anything similar.2007 Corvette LS3 File 8 WOT Fuel 1.hpt2007 Corvette Base LS3 Log 14 WOT.hpl2007 Corvette Base LS3 Log 15 WOT.hpl2007 Corvette Z06 Log 31.1 WOT.hpl

[Alvin]

I suspect this is a scanner bug and prehaps that channel is polling too fast.

I think it would be a good idea to remove all burst knock just in case.

[Andrew Woodward]

Do you mean you think the data log is actually causing the commanded timing to fluctuate or just a visual error? I can confirm by my dyno that the timing is in fact messing up in the car. I can feel it hesitate and the loss of power.

[Alvin]

I don't think you'd be able to feel 2ish degrees that it varies. The timing is so low on what looks to be a NA car i'd bet that is what is making you feel like it is messing up the car. If the timing is that low it will have a surge at full throttle and it will show in the graph.

I'd remove the burst knock like I said to be sure it isn't that.

[Andrew Woodward]

In the data log you can see that timing drops as low as 8 degrees at 3000rpm where I am commanding 17. That's the whole problem. I have used this base timing map many times for initial dyno pulls without this issue. As for burst knock I can try that but I have never had to adjust that before.