Spark drop without any KR?

[dbb2797]

I'm trying to understand something that I notice is occurring. I run my car at the track so I need it as consistent as possible. I launch from a 2-step, run it in open loop, shut off all KR and have zeroed all the spark modifiers I can find. I have the

What I notice is after I launch and as I go through 1st gear, the spark fluctuates. It goes from 25 down to 22 and back up a few times. If you look at my RPM going through first gear in the log, notice how it starts strong, then dips, then accelerates again into the gear shift? That also seems to correlate with the spark fluctuations that I'm seeing. I'm not 100% sure its' the spark causing the dip in the RPM ramp up, but it feels like it is correlated.

After I shift into 2nd, and after the converter locks, it is fairly steady from that point on.

Take a look at the attached log.

Notice the ramp up at launch for RPM, the dip in acceleration at about 7:03:133 and then starts ramping up again at 7:04:355. Also notice the spark dips throughout that RPM acceleration fall off too.

Any thoughts on what might be causing this?

[murfie]

The TQ converter getting to its stall speed is causing the dip in the RPM in first. You can correlate it with TCC slip.

Through out the run you are in base spark source and timing is less than borderline. Your lambda spark modifier is zeroed out. You would be getting timing pulled form IATs in first and second then added after that going from 135* to 85* IATs. ECT would remain pretty consistent.

I've seen the cylinder to cylinder offset table cause it to sit in base spark source as this table is -2 in the range your log shows. I think zeroing that table should help you stay in borderline and get you 2* more timing while adding consistently. cylinder to cylinder would cause these fast jumps up and down as some cylinders having it applied and other do not.
log spark source.PNG


Base tables in orange boxes.
base spark source.PNG

[dbb2797]

wow really great info murfie. All your suggestions make sense. I will make the updates and give them a test this week.

[murfie]

Just FYI this can happen with the commanded lambda values as well from the fuel imbalance tables. The scanner can only poll so fast and so it looks like the PID is going up and down when really its just getting its value on different cylinders. for example above 5250 and .8 load your cylinder 3 is going to command 8% more fuel than the other cylinders. Does it need it? I cant say as it would take 8 O2 sensors to really tell. This could be the small difference in your lambda bank to bank.

[dbb2797]

Gotcha. I may look at equalizing the fuel imbalance tables. I'm going to a test and tune tomorrow so I'll give a couple of these ideas some experimentation.

[dbb2797]

I couldn't make it to the track so here are some street pulls to get logging. I zero'd everything I could find in base spark and equalized all the fuel imbalance tables. . It's definitely much, much smoother. Granted since they are street pulls, the IAT is really low, but once I get WOT the spark pretty much stays right at 24.3, even during shifts. Which I do want it completely steady so this is a definite plus. But I am still in base, and it looks like I'm exactly 1* below my MBT and Borderline tables.

Any more thoughts Murfie?

[wayno]

looks like its coming from the lambda base mbt table.

[murfie]

Base MBT table.

Base MBT.PNG

[dbb2797]

ahh yes, that is definitely it! That should hopefully be one of the last pieces of the puzzle to get steady and predictable spark. Thanks Murfie and Wayno!

[longstroke]

It was tip in retard on mine. It was pulling 3-5 degrees for no apparent reason at wot. I showed it to Eric one day at the track and he zeroed the tip in retard and it was gone.

[elerico]

ahh yes, that is definitely it! That should hopefully be one of the last pieces of the puzzle to get steady and predictable spark. Thanks Murfie and Wayno!

do you have the final tune ?

did you zero out the base mbt table