|
|
| Tuning With The HKS S-AFR |
 |
|
Now, before I begin, it's important to note that while I tuned the car using an HKS AFR, the concept is exactly the same when using the APEXi SAFC, since they both modify the MAP sensor output to the PCM. Anyhoo, here we go. When my 33# injectors ran out of fuel at about 6psi, I swapped in the modified DSM injectors I'd made for myself a while ago, which are 42.8#s (450cc) They will idle in the car on the stock fuel system with no modification, but the A/F is like 10 or below, and it is rough as all hell. However, lucky for me, the HKS AFR has a built in dial that is used exclusively for idle adjustment, which makes it pretty easy for me to get the idle decent. However, I still have to wait for the stock O2 sensor to warm up enough to get into closed loop operation before the car will run correctly, since in closed loop when not at WOT, it just totally dumps tons of fuel and the car basically won't move. Anyhoo, after the car warms up, I move the idle adjustment down from -23% to -6%, and it idles quite well. After I got down the idle control procedure, I went about tuning for basic cruising and slow accelleration under closed loop operation. You might notice that the computer richens the mix a bit under moderate accelleration. Well, when you're using 43# injectors with a PCM tuned for 19# injectors, when it decides to richen the mix a "little", the car pretty much chokes the shit out of itself on fuel and almost dies. So, in order to get the A/F under control during these conditions, I drastically cut back the fuel from 1000-3000 RPM, since I know I'm never going to floor this car under 3000 RPM. In addition, the turbo I have on there will never spool to any considerable degree under 4000 RPM, so I know I don't need a whole hell of a lot of fuel until then. When I was able to cruise around without too many A/F problems under general driving conditions, I took the car out onto a back country road and tried tuning for full throttle conditions from 4000 RPM to redline. With no tuning, the car was completely unable to deal with being floored. The instant I would punch it, the A/F would drop to 10 (or below, actually...I don't think my wideband can read below 10) and the car would sputter and almost choke itself out on too much fuel. Since my turbo doesn't spool until 4500 RPM, I originally began by just tuning from 4500-redline. However, it soon became apparent that no matter how much I leaned it out, I couldn't get the A/F into an even remotely acceptable range. To solve this problem, I then tuned down the 4000 RPM point in order to drop some fuel out before boost came on, to try and get more fuel out later in the RPM band. This modification had a larger effect than I anticipated, and the A/F under boost then became very lean. It was at this time that I remembered, from tuning the purple car, that on the stock cams, the PCM dumps a huge amount of fuel right at 3800 RPM. So, right before boost came on, the computer was apparently dumping too much fuel and was unable to pare it back later in the RPMs. Taking a bit away right where it was needed fixed a lot down the line. I retuned the later RPMs with the new value at 4000 and all was decently well. To the right, you can see the correction values I used to achieve the A/F ratios shown in the graph below.
|
As you can see to the right, I still have some tuning to do, but the rest shouldn't be too hard. Optimally, I'd like an A/F of 11.5-12.2 throughout the entire boosted RPM range. If I pull a couple more percent out of the 4000 RPM point, as well as from the 4500 and maybe 5000 points, everything should be in the proper range. The 6500 point can probably lose another percent or two, as well, just to tune it up a little bit. I should mention that my EGT readings throughout the boosted range were 1250-1350 degrees F, which is well within the limits of the engine. I suggest tuning with both wideband A/F AND EGT readings, in order to get the safest tune possible while producing the most power. The lesson learned from this tuning session is that, despite all the naysayers' negative opinions on the subject of boosted tuning with a MAP-based fuel controller, it is, in fact, possible to get a safe, accurate tune with these simple tools. Be aware, however, that when tuning in this fashion, you can only take AWAY fuel. You can't ADD any fuel. Therefore, make sure that you have pretty big injectors before you start and you'll be all good to go. Yayer!
|
|
|
|
|
|
