Hooked my widaband o2 up last night. Stock ECU, pre modifications. Here are the points of interest, sorry if these are obvious or "no sh*t" revelations.
The ECU has 2 main priorities.
1. Low nitrogen oxide emissions(the ultimate priority)
2. Limit the possibility of engine damage.
Explanation of #1: The ECU does whatever it takes to keep AFR at stoichiometric. Best balance of emissions, lowest nitrogen oxide, best catalytic converter efficiency. It stays stoich at idle, during most acceleration events and at cruise.
Explanation of #2: When it strays from stoich, boy does it stray. Mash the throttle and go for it. It will briefly dip down into 13:1+ range(acceleration enrichment), then quickly go back to stoich until about 4300RPM, where it goes open loop and WAY rich. 10.5:1 and below. Obviously to stave off detonation.
Some other interesting things I noticed. I wanted to know why gas mileage was so poor sometimes for a car of this size and power . Watching the APR display during my commute answers this question. I feel It has allot to do with the 2 priorities described above. 1. Emissions, 2. Limit chances of engine damage.
As you would expect, on the highway 14.7 AFR is the name of the game. Once again. Best balance of emissions, though not best for economy. There was one interesting thing I didn't expect. On slight long hills, medium long hills etc...It will dip down to 12.5-13.8(usually hangs in the 13 range). Even if its just a slight grade(but long) it will hang out in the mid 13 range until the road goes flat. So I think in the interest of satisfying priority #2, the ECU goes mildly rich in those long but low to medium load conditions. I didn't expect the ECU to see the need to go any more rich than 14.7 unless loads were high.
So on the highway(for my car at least) allot of time is spent on the rich side of 14.7. This would explain the lackluster highway mileage.
Things I want to know:
Is the ECU sensing detonation on those long light load conditions and adding more fuel? Does it go in the 13:1 range to smoothly ad a little more power for those conditions? Or is it just to maintain engine health and make sure detonation never occurs?
My wideband has a simulated narrow band output with adjustable stoich point. I'm going to play with that and see how it effects mileage, power.
One of the other things I was interested in is the tendency for the car to buck at low speeds in traffic. I had a theory that maybe the injectors were shutting down on overrun (when you let off the gas but are still in gear). I was thinking maybe this would create the abrupt on/off situation that leads to the tendency to buck. The answer is no. The ECU does shut off the injectors on overrun consistently, as soon as it can, and for as long as it can. Just not at speeds that low.
The ECU has 2 main priorities.
1. Low nitrogen oxide emissions(the ultimate priority)
2. Limit the possibility of engine damage.
Explanation of #1: The ECU does whatever it takes to keep AFR at stoichiometric. Best balance of emissions, lowest nitrogen oxide, best catalytic converter efficiency. It stays stoich at idle, during most acceleration events and at cruise.
Explanation of #2: When it strays from stoich, boy does it stray. Mash the throttle and go for it. It will briefly dip down into 13:1+ range(acceleration enrichment), then quickly go back to stoich until about 4300RPM, where it goes open loop and WAY rich. 10.5:1 and below. Obviously to stave off detonation.
Some other interesting things I noticed. I wanted to know why gas mileage was so poor sometimes for a car of this size and power . Watching the APR display during my commute answers this question. I feel It has allot to do with the 2 priorities described above. 1. Emissions, 2. Limit chances of engine damage.
As you would expect, on the highway 14.7 AFR is the name of the game. Once again. Best balance of emissions, though not best for economy. There was one interesting thing I didn't expect. On slight long hills, medium long hills etc...It will dip down to 12.5-13.8(usually hangs in the 13 range). Even if its just a slight grade(but long) it will hang out in the mid 13 range until the road goes flat. So I think in the interest of satisfying priority #2, the ECU goes mildly rich in those long but low to medium load conditions. I didn't expect the ECU to see the need to go any more rich than 14.7 unless loads were high.
So on the highway(for my car at least) allot of time is spent on the rich side of 14.7. This would explain the lackluster highway mileage.
Things I want to know:
Is the ECU sensing detonation on those long light load conditions and adding more fuel? Does it go in the 13:1 range to smoothly ad a little more power for those conditions? Or is it just to maintain engine health and make sure detonation never occurs?
My wideband has a simulated narrow band output with adjustable stoich point. I'm going to play with that and see how it effects mileage, power.
One of the other things I was interested in is the tendency for the car to buck at low speeds in traffic. I had a theory that maybe the injectors were shutting down on overrun (when you let off the gas but are still in gear). I was thinking maybe this would create the abrupt on/off situation that leads to the tendency to buck. The answer is no. The ECU does shut off the injectors on overrun consistently, as soon as it can, and for as long as it can. Just not at speeds that low.
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