Hello,
I would like to have a discussion about a few areas of this vehicles tune that are bothering me. I want to start by saying I am no expert, but I enjoy tuning, and have tuned many Gen 3 cars and a couple of Gen 4 cars. This one in particular is my own; its a bone stock 09 CTS-v I recently decided I wanted to run on flex fuel and finally dial in.
Things I do not like about the way the car drives: The transmission is very clunky, shifting is inconsistent. I get it, its a Cadillac, not a Camaro, but to be honest its downright sloppy and still shifts hard at the wrong times. The torque management is heavy. The ramp up to power is very slow, and the brake torque really makes for poor burnouts. So these are some of thing things I set out to correct.
I spent yesterday doing a little tuning. I will be honest and say I forgot I could monitor fuel pressure so I didn't. Now, for comparison, I am stepping out of a 05 Corvette with a roots blower making 550+whp and a 6 speed manual so my expectations are a little skewed. That car ran deka 60s at 50psi and a duty cycle around 60%. I had an aux fuel system so plenty of pump. I was disappointed to find this car running at 90% DC on 93 pump at 11.3 AFR at WOT. No room for the E85 I wanted to run
So I began doing some research. Now historically I haven't touched the FPCM on any of the cars I tuned and I am honesty not familiar with how it functions or what the real effect of tuning these tables would be. I did a search and the information I found was limited. Is there a way to adjust my fuel pressure or pump duty cycle in a way that will real world impact my fueling and give me just a little extra duty cycle to run E85? If someone could provide a good link or article or just wants to generally discuss FPCM I am interested.
Next, Knock retard on these cars. First thing I did was take my bone stock car for a data long for about 20 minutes. I was shocked to find that my knock sensors were pulling between 2-6 degrees everywhere in the factory tune file. Car pull strong up top but my god, it seems like GMs strategy her is feed it timing and let it knock retard its way into a safe place. I am still fighting off a degree here and there but the reality is I knocked the timing down to 20 deg from 23 factory and the car feels worse. I am swapping plugs on Sunday to coppers to see if I can pull in a few more degrees safely, as the car "feels" like it keeps making more power each degree it goes up. Sometimes I get a good pull without knock at 23 degrees and other times it pulls 6 degrees and the car feels like a dog. I believe some of this to be false knock but I am not sure yet. If it is we may need to discuss slightly desensitizing the sensors.
The transmission. Simply since I am running on here.... can I remove any of the torque management and not slam downshifts in the most brutal way possible? I actually left all the transmission side torque mgt on only removing engine side torque mgt. I think the table really screwing me over is the "minimum final torque mgt" table as I took out the negative values and replaced them with 10 degrees inbetween shifts to keep the car pulling. Upshifts are great, fast, firm quick... downshifts are miserable, inaccurate, and brutal. Whats the strategy to make it live and make me happy?
Finally, relating to transmission. I've done a ton of research on this and can't find any specific proven method for tuning virtual torque tables. Everyone just does what ive been doing and ups the tables about 10%. Doing this works, but bothers me. I wish there was an explanation for an accurate way to tune these tables. Its driving me nuts...
Feel free to comment or answer one or move of these.... Glad I am able to share my experiences here.
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