I do more reading than posting on this forum, but I spent the last month tuning my 2008 Convertible, so I figured I'd share some information I've learned.

First of all, thanks to ktoonsez and Bluecat (and whoever else has posted good information about tuning the '08's). It would have been much harder to tune without the EQ<>VE software.

I started by tuning the VE table, then tuned the MAF. I run with LTFT disabled. Car runs great now. Haven't taken it to the track yet -- I'm pretty sure I'll get booted after one run since my car is a vert.

Anyway, here are some of the things I've learned:

1) Very important to use gradual throttle changes when logging data. During throttle transitions, you get false lean/rich readings that skew your data.

2) Under 4k RPM (or whatever you've set for Dynamic Airflow High RPM disable), the ECU uses a combination of VE table and MAF to calculate airflow, not just one or the other. So once my VE table was tuned, I tuned MAF for all cells, then turned everything back on and tweaked as necessary.

3) After some heat-soaked data logging, when I would start the car and start logging again, my AFR's were about 10% rich. Everywhere. At first I thought my tune was jacked up, but I found that if I went WOT one time, AFR's would return to normal. I never found out for sure what the issue was.

4) I was able to eliminate the dreaded "popping" during deceleration by adjusting the DFCO entry spark.

5) I didn't advance timing anywhere -- I ended up removing timing to eliminate knock retard in my data logs. The knock sensors are very touchy, but I didn't want to reduce the sensitivity on them.

6) Once I finished tuning, I would get a SERVICE ELECTRICAL SYSTEM message occasionally. I realized that I had P0420 and P0430 DTC's set to: 2- No MIL light. Once I changed them to: 3 - No Error Reported, the SES message went away for good.

I'm sure I'm forgetting some things. I'll post more if/when I remember.

 

Did you do any WOT with a wide band O2?

 

Yes, I bought HPTuners Pro and a W/B O2 sensor and tuned WOT after I tuned partial throttle.

I wish I would have logged more data before I started tuning so I could see how much timing the car was actually running compared to the timing tables. I'm wondering if the "knock learn" pulls timing so you run somewhere between the high and low octane tables. I'll hook everything back up in a couple weeks and see what kind of timing she's running.

 

you tuned the VE table ?

 

Contrary to popular opinion, more ignition advance does not automatically increase power even in the absence of knock retard. I have seen cars make more power at 4° less advance before the appearance of KR. In some cases, too rich A/F ratio causes KR and huge power reduction.

Tuning on a load bearing dyno really helps determine how much fuel and ignition advance the engine needs to make the most power.

Today, I witnessed a fellow forum member gain 30 rwhp (10%) and and equal amount of torque over a well known mail order tune. I won't say who's it was, but it confirms what I have been seen in the past.

 

Yes -- well, the "virtual" VE table that the '08's have. I used the EQ<>VE software that ktoonsez posted.

Mez, yeah I'd like to get on a dyno to fine tune the fuel and spark. I'd be curious to see that mail order tune -- that's a big jump.

 

As far as the afr running richer, what was the EQ ratio at the time. If you were in open loop there are some tables that will request say a EQ of 1.05 etc which would run you 5% richer until the car went into closed loop and these are based off ECT, IAT, IVT. Go back and look, but your car was probably doing what it was supposed to be doing according the calibration that was in it.

 

A multiplier of 1.05 translates to an EQ Ratio of 0.952. EQ Ratio is lambda on these. Why GM didn't just make all the multipliers work towards a lambda value instead of inverse lambda, I'll never know.