[mtimmons]

Ok guys, let’s all take a breath and let me explain what is going on .

We’re past the days where you throw a vehicle on the dyno, do a couple of pulls, and look at a set of numbers to see what will happen out on the road which is obviously where your engine management “corrections” should be “correct.” This comes up every time we get into a new vehicle population and guys try to wrap their arms around what’s happening in the engine, so it’s not entirely surprising.
Looking at the chart, the Unichip is leaning out the AFR exactly the way it’s supposed to; the problem isn’t with what the Unichip is doing, the problem is the value the truck is running without the Unichip installed. What’s driving that is what’s happening with the Tundra on the dyno, not because the Unichip’s working incorrectly or is programmed incorrectly. There is only one set of conditions the stock ECU keeps the engine this lean and it’s the same set of conditions replicated by a typical dyno pull.
Briefly… if you watch the truck in the real world, how it behaves after transitioning to Open Loop depends on a number of factors including among others commanded load, calculated load, time, and transmission actions. If you’re on a relatively flat road and not towing and stab the throttle, the engine behaves completely differently than if you’re hauling something. If you open the throttle below the transmission downshift threshold, the engine stays relatively lean to improve mileage… that’s why the truck on this dyno is lean without the Unichip installed. Even though the engine is at full load, the throttle onset rate at the beginning of the pull was sufficiently slow that the transmission didn’t downshift.
However, when the truck stays under a sustained load – indicated to the ECU by a combination of commanded load and time under load, the engine substantially enriches. You can see this by watching the AFR while towing or by pushing the throttle aggressively enough that the transmission immediately downshifts, or by staying in the throttle after the transmission upshifts during acceleration, or by keeping the load high by hauling something, going up a hill, or both. In each of those circumstances, the AFR goes richer which makes the Unichip’s correction exactly correct.
Put what happened into the real world and let’s see why we set things up like we do…

• Use Case 1 – standing start like a drag race. You smack the throttle and the engine accelerates very much like the dyno pull although just a little richer because of the cooler temperatures on the road. As soon as the transmission upshifts to 2nd gear, the AFR drops and the Unichip’s correction is perfect.
• Use Case 2 – hard acceleration from a steady-state cruising condition. You smack the throttle, the transmission immediately downshifts, the immediately AFR drops, and the Unichip’s correction is again perfect.
• Use Case 3 – sustained high load due to towing or climbing a grade. Assuming you don’t immediately transition to Use Case 2 with a transmission downshift, as soon as the ECU detects the high calculated load for a (short) predetermined period, the AFR drops and the Unichip’s correction is perfect.

As we’ve discussed, the “total” answer to these sort of questions are way, way, way more complicated but in a nut shell there’s no problem with what’s happening in the case study. Dyno’s are really good for some things… we use ours every day. If you know what the vehicle is doing, why it’s doing what it’s doing, and how that compares with what that same vehicle does on the road in the real world, dyno’s are great tools. If you don’t know all of those things, dyno’s are a waste of time and raise far more questions than they answer. Nobody buys a vehicle to drive it on the dyno, and unless a particular vehicle functions exactly the same way on the dyno as it does on the street, we don’t make our calibrations for the dyno, we make them for where the vehicle is being used. Look at it this way, given that the truck behaves differently on the dyno and the street (which they almost all do today, including this Tundra), where do you want your engine management solution to give you power?

Please, if anyone has felt like our customer service has been poor, let me know. Also, when we have someone posts info like that we are going to look in to the problem, figure out what is what and then get back to everyone when we have the correct answer.