I just thought I'd share some tuning information with you folks. Hopefully, you'll find it useful. This could be long so grab some popcorn.
A few weeks ago I dynoed my car and when looking at the scans, I noticed that it would start out rich early in the pull, and slowly lean out as the RPMs climbed. In last year's setup, I would have assumed that the fuel pump and lines were straining to keep up with the demands of the motor, but this year it clearly is not the case. I have a huge Weldon fuel pump, all new wiring, and large SS braided fuel lines. That told me that I simply need to program my PCM for a little more fuel, and I wouldn't have to worry about volume, as the system can now keep up.
I decided to burn a new .bin file and have it ready, but not to load it. At least not until I had a baseline run at the track to make sure that my track readings would have agreed with my dyno findings. This is a subtle point here that many people are probably not aware of. Because of the way that our PCM does fueling during power enrichment (PE), there is a strong time component to the calculations of the commanded A/F ratio. This time component is likely to give you different results by the simple fact that a dyno pull (3rd gear) will last for about 5 seconds, while a track run will last 11-13 seconds depending on the car.
There are three PE tables in our PCMs that control the target AFR that the PCM shoots for. It is this target A/F ratio that determines just how much fuel the PCM will dole out while at WOT. (For this reason, it is very useful for people to include the commanded AFR in their log scans, as it lets you know what the PCM is "trying" to do.)
Anyway the tables are Base vs ECT, Additional vs TPS, and additional vs RPM vs time. The commanded AFR that the PCM will shoot for is the sum of the returned values from all three tables. The Base vs ECT represents a simple 2 dimensional curve that sets the AFR as a function of ECT. Basically it calls for a richer AFR when the ECT is cold, and a leaner AFT when the ECT is hot. For all practical purposes though, it is flat throughout the entire "normal" range of ECT, so in loose terms, it can be considered as a constant once the car is up to temp.
The second table, additional vs TPS also represents a 2 dimensional curve. The purpose of this table to lean out the mix slightly for low TPS positions, and leave the AFR unchanged for moderate to high TPS positions. In my stock table, this table goes to 0 for any TPS greater than 49%.
The third table and the most interesting one represents a three dimensional surface that sets the AFR depending on both RPM AND the amount of time that the vehicle has been in PE mode. In short it richens up the fuel gradually as the RPMs climb, but it also richens up the car gradually for prolonged WOT bursts as time goes on in an effort to cool things down a bit.
When I decided to make a new file, I also decided that the right fix would have been to work in the third table, additional vs RPM vs time. The base table would have been a straightforward enough fix for the leaning part, but also the wrong one. I only wanted to richen up the higher RPMs, not the entire range. The additional vs TPS table would have also been the wrong table as when racing, I have a binary throttle. It's either on or off.
My changes to the add vs RPM vs time table were in two dimensions. I decided that I wanted to increase the fuel a little more for RPMs past 4800, but also I wanted the additional fueling to come on sooner than the stock table called for. In essence I left the early part of the table alone, but pulled in the heavier part of the enriching by 3.2 seconds. I burned a new file and left it on my laptop's hard drive.
OK, now that we have the background out of the way, fast forward to last weekend when I took my car to th etrack. after my first full pass, I looked at the logs and saw the same trend. The fueling in the first two gears looked pretty good, but as soon as the shifted into third and the load increased, My O2's* dropped and stayed betwen 860 and 890 for the entire length of the run. I decided that the results were more or less what I expected and dropped in the new PCM file.
When I ran again, the results were right on the money. Everything looked pretty much the same in the first two gears, and once it shifted into third gear, my O2s ranged from 930 to 905. That's pretty much what I was shooting for. As a side note, the car picked up an additional .8 MPH in the back half of the 1/4 mile as opposed to the previous run.
* - I realize that using the narrowband O2 sensor for fuel tuning is questionable but until the wideband goes in (soon) with support from HP Tuners, it will have to do.
John
A few weeks ago I dynoed my car and when looking at the scans, I noticed that it would start out rich early in the pull, and slowly lean out as the RPMs climbed. In last year's setup, I would have assumed that the fuel pump and lines were straining to keep up with the demands of the motor, but this year it clearly is not the case. I have a huge Weldon fuel pump, all new wiring, and large SS braided fuel lines. That told me that I simply need to program my PCM for a little more fuel, and I wouldn't have to worry about volume, as the system can now keep up.
I decided to burn a new .bin file and have it ready, but not to load it. At least not until I had a baseline run at the track to make sure that my track readings would have agreed with my dyno findings. This is a subtle point here that many people are probably not aware of. Because of the way that our PCM does fueling during power enrichment (PE), there is a strong time component to the calculations of the commanded A/F ratio. This time component is likely to give you different results by the simple fact that a dyno pull (3rd gear) will last for about 5 seconds, while a track run will last 11-13 seconds depending on the car.
There are three PE tables in our PCMs that control the target AFR that the PCM shoots for. It is this target A/F ratio that determines just how much fuel the PCM will dole out while at WOT. (For this reason, it is very useful for people to include the commanded AFR in their log scans, as it lets you know what the PCM is "trying" to do.)
Anyway the tables are Base vs ECT, Additional vs TPS, and additional vs RPM vs time. The commanded AFR that the PCM will shoot for is the sum of the returned values from all three tables. The Base vs ECT represents a simple 2 dimensional curve that sets the AFR as a function of ECT. Basically it calls for a richer AFR when the ECT is cold, and a leaner AFT when the ECT is hot. For all practical purposes though, it is flat throughout the entire "normal" range of ECT, so in loose terms, it can be considered as a constant once the car is up to temp.
The second table, additional vs TPS also represents a 2 dimensional curve. The purpose of this table to lean out the mix slightly for low TPS positions, and leave the AFR unchanged for moderate to high TPS positions. In my stock table, this table goes to 0 for any TPS greater than 49%.
The third table and the most interesting one represents a three dimensional surface that sets the AFR depending on both RPM AND the amount of time that the vehicle has been in PE mode. In short it richens up the fuel gradually as the RPMs climb, but it also richens up the car gradually for prolonged WOT bursts as time goes on in an effort to cool things down a bit.
When I decided to make a new file, I also decided that the right fix would have been to work in the third table, additional vs RPM vs time. The base table would have been a straightforward enough fix for the leaning part, but also the wrong one. I only wanted to richen up the higher RPMs, not the entire range. The additional vs TPS table would have also been the wrong table as when racing, I have a binary throttle. It's either on or off.
My changes to the add vs RPM vs time table were in two dimensions. I decided that I wanted to increase the fuel a little more for RPMs past 4800, but also I wanted the additional fueling to come on sooner than the stock table called for. In essence I left the early part of the table alone, but pulled in the heavier part of the enriching by 3.2 seconds. I burned a new file and left it on my laptop's hard drive.
OK, now that we have the background out of the way, fast forward to last weekend when I took my car to th etrack. after my first full pass, I looked at the logs and saw the same trend. The fueling in the first two gears looked pretty good, but as soon as the shifted into third and the load increased, My O2's* dropped and stayed betwen 860 and 890 for the entire length of the run. I decided that the results were more or less what I expected and dropped in the new PCM file.
When I ran again, the results were right on the money. Everything looked pretty much the same in the first two gears, and once it shifted into third gear, my O2s ranged from 930 to 905. That's pretty much what I was shooting for. As a side note, the car picked up an additional .8 MPH in the back half of the 1/4 mile as opposed to the previous run.
* - I realize that using the narrowband O2 sensor for fuel tuning is questionable but until the wideband goes in (soon) with support from HP Tuners, it will have to do.
John
