# Technical observations while scanning



## XtremeRevolution (Jan 19, 2012)

I did some scanning with Torque this morning on my way to work (in my Eco MT) after discovering I can add a GM set of PIDs to show KR. In any case, here are some observations I've made:

1. Your throttle position is not what you command it to be. The PCM takes your throttle input and interprets it, then makes a decision for you with regard to how much throttle to actually open in the throttle body. It's generally accepted that high throttle at low RPMs makes the engine more susceptible to knock due to there being more time for the fuel to ignite on its own. Driving in 6th gear at 40mph turning somewhere in the 1200-1300RPM range, you can floor it but the car won't actually open the throttle any more than 50% and you stay in closed loop mode. 

2. It takes quite a bit of throttle to get the car to go into open loop mode. When it does, PE (power enrich) commands an AFR of 13.78:1. I found this to be a bit surprising considering the 12:1 and 12.5:1 I was tuning in HPTuners on the L67. Is it just me, or does that sound fairly lean? Interesting observation nonetheless. 

3. There is indeed some knock at very low RPMs with "high" throttle, but it really is insignificant. My peak never exceeded 2 degrees of KR. 

4. That intercooler will definitely warm up the air charge, presumably due to heat soak from the radiator and nearby turbo and exhaust components. Ambient temps were in the 70 degree range this morning, while IATs were up in the 76-78 range. However, the IATs never went more than 8 degrees over ambient temps. I'm going to put the resonator duct back in on Wednesday and run another scan to see if that difference changes.


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## obermd (Mar 3, 2012)

XtremeRevolution said:


> 1. Your throttle position is not what you command it to be. The PCM takes your throttle input and interprets it, then makes a decision for you with regard to how much throttle to actually open in the throttle body. It's generally accepted that high throttle at low RPMs makes the engine more susceptible to knock due to there being more time for the fuel to ignite on its own. Driving in 6th gear at 40mph turning somewhere in the 1200-1300RPM range, you can floor it but the car won't actually open the throttle any more than 50% and you stay in closed loop mode.


It makes sense that in a drive by wire car you don't have direct control over the throttle and injectors. Also, I'd be interested in seeing results of accelerating from low RPM vs downshifting and accelerating. We know the latter results in faster acceleration, but which one saves fuel when you have time for the slower acceleration?


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## XtremeRevolution (Jan 19, 2012)

obermd said:


> It makes sense that in a drive by wire car you don't have direct control over the throttle and injectors. Also, I'd be interested in seeing results of accelerating from low RPM vs downshifting and accelerating. We know the latter results in faster acceleration, but which one saves fuel when you have time for the slower acceleration?


I can only speak for my own driving methods and their results, which for the last few tanks of gas have consistently beaten the EPA highway rating, with ~75% city driving. My understanding is that so long as you're aren't registering any consequential amount of KR, you will achieve better fuel economy accelerating slower. Your engine will always maintain a ~14.7 AFR regardless of RPM and load while in closed loop mode (the exception of course being hard acceleration in closed loop mode).


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## ErikBEggs (Aug 20, 2011)

I assmuing this was done with 93 Octane? Do it in 87 so we can see


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## XtremeRevolution (Jan 19, 2012)

ErikBEggs said:


> I assmuing this was done with 93 Octane? Do it in 87 so we can see


Eek! It might actually get warmer around here in the next week, lol. I'd really rather not. I can almost guarantee myself some KR and a drop in fuel economy, and I'd have to deal with it for at least a week.


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## ErikBEggs (Aug 20, 2011)

89? Come on man...


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## XtremeRevolution (Jan 19, 2012)

ErikBEggs said:


> 89? Come on man...


89 I might consider. I didn't do that badly with 89. In straight up winter driving, I noticed a distinct difference with 89 octane over 87 octane. I'll think about it.


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