This is a re-cal of my car after getting it running again (08/C6 Z06). I just got the heads back. I had them worked for a set of Crower roller rockers, along with some additional port work. While I was at it, I port matched the Fast intake runners and sent the 90 mm TB out to Vmax for his cnc porting. I also changed O2 sensors to some NTK direct replacements that has slightly longer leads. I am using the custom OS. I moved to the custom OS for no other reason than to have VE tables to work with.
So yesterday I finally had a decent day to re-cal the tune. I do not have access to a dyno, so I use a long stretch of road that I can monitor my lap top without any real danger of traffic. Yes, I know, a dyno is preferable. If I had one, or access to one, I’d use it.
I’ve played around with tuning this car dozens and dozens of times. I have a routine now…..
1) Check / recalibrate VE with STFT’s. All VE multipliers set to 1. Closed loop enabled, PE disabled as well as all the other fuel adders like cat protection. MAF disabled, MIL set to light up on first error so I now it’s disabled. I keep engine speed under 4500. LTFT’s disabled.
2) Check / recalibrate MAF with STFT’s. I just roll to MAF after VE. Leave all the VE tables alone, and just re-enable MAF. LTFT’s disabled as with VE calibration.
3) Install WB, check / recalibrate WOT MAF with PE enabled, cat protection, clutch and deceleration fuel cut off disabled. I’ll take a couple runs in second gear to read line, WOT from a fast enough roll to keep the tires from breaking loose.
VE calibration took about thirty minutes. Two logs, some tweaks, and a final third verification log and I was done. 3% max STFT error. Then I moved to MAF and ran into problems. I’m not sure if I did something wrong, I have a sensor problem, or my expectations are out of line. Normally MAF cal is the quickest and easiest for me to get through. Again, I was using STFT’s. I had my histogram set to Average. I took care to keep rpm steady in each histogram cell long enough to get 25 hits, then slowly move to the next. I usually do this in second gear. The first log was showing STFT’s were an average of about 10% to the negative in some areas of the low MAF table. I copied the histogram average table, and used the paste special, multiply % into the HPT MAF table. Saved the new calibration with a new file name, then wrote the calibration to the ECM. Took a log, and things were closer. The second round I used the multiply half % function. Well this time when I took a log, STFT’s were out in the weeds, showing up to a negative 25%. Not really understanding what went wrong, I wrote the previous calibration back to the ECM. Took a drive and the STFT’s were still way out in the weeds. I then experimented and found that the STFT’s would be close to a zero % average in second gear, steady and slow rpm increase, but they’d be way off in the same problem MAF cells while in fourth, fifth or sixth gear. So this is where I’m a bit perplexed. What would it matter if the engine is pulling the same amount of air to support a stoic combustion (as read in the MAF frequency table cells), but at different rpm’s?? Could this be due to velocity through the TB? Or, is this a symptom of a weak MAF sensor? Or, is this to be expected? Would using LTFT’s be a better method for calibrating the low MAF table?
One other thing I’m noticing, that’s a new thing I’ve not ever had happen, is that when I park the car after a log, and it comes to an idle, the rpm will raise to about 1600 and will not drop. Thinking this was a minimum idle air flow thing, I recalibrated that table. I use the adaptive idle spark histogram technique for calibrating this table. I will use the HPT controls to raise / lower idle and log error then adjust the min air flow table. I copy all the 1200 rpm values into the cells over 1200 rpm. Well I did this, but it did not stop this parked idle rpm creep. It does not do this when I have the MAF disabled and the car is running off the VE tables. It only does this with VE disabled and running off MAF.
I probably wasted about three hours taking logs and sending new calibrations to the ECM. I finally decided I better just give up, and figure out what is happening and what I’m either doing wrong, or if I should look for a mechanical problem. I did order a new MAF sensor as well, but it will not get to me for a few days.
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Originally Posted by SultanHassanMasTuning
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