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Old 03-20-2012, 08:29 PM   #64
roger 04 rt OP
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Joined: Nov 2011
Location: Massachusetts
Oddometer: 2,365
Yesterday I was able to borrow an oscilloscope for a few hours. It was very interesting to see the raw waveforms being sent by the LC-1 (Innovate Motorsports) to the narrowband input on the Motronic ECU. The persistence of the scope I used wasn't long enough for photos so I'll just attempt to describe what I measured.

As a baseline, if I was examining a functional narrowband sensor during Closed Loop operation, I would see a waveform that simply alternated between 100mV for half a second or so and then 900 mV for half a second or so, in a repeating cycle until the Closed Loop mode ended--usually due to a change of throttle. The Motronic would be creating this alternation by steadily increasing its injector pulse width until the O2 sensor jumped to 900mV. Then in would start slowly decreasing the pulse width until the O2 sensor voltage abruptly fell to 100mV--this is what creates Closed Loop operation. The frequency of this alternation would be about once per second or so. (As an aside, if the fueling table said that the average pulse width for 14.7:1 was, for example, 2.00 mS; but the average pulse width for Closed Loop was 2.08 mS; then the Motronic would "learn" an "adaptation value" of +4% and it would start there next time, it would also add 4% to similar Open Loop fueling. Also, in Closed Loop I might have seen a +/- 3-4% spread between richest and leanest values, for a 6 to 8% swing in fueling.

What I learned by looking at the LC-1 real time waveforms (there are two analog outputs--one for the motronic and one for the gauge) was the following:

1) As I have the LC-1 set up, the Motronic is able to alternate the mixture once per second, just as with the narrowband sensor--this is good, it means the LC-1 solution is compatible with the Motronic.

2) In Closed Loop, the Motronic tries a new step every 30 to 50 mS (50 thousandths of a second).

3) Each Motronic fueling step is about 1%. So if it started at, say, 2.00 mS it next tries 2.02 mS, then 2.04 and so on, same step size on the ramp down.

4) The LC-1 is nearly instantaneous in its response. As a result, I observed a narrow spread of +/- 1% to +/- 2%. The stock narrowband O2 sensor is 2 to 4 times as large because it responds more slowly, which creates a variation that is probably felt as surging.

5) Because the LC-1 is so fast, the 100 mV to 900 mV transition isn't a single jump from one voltage to another, it is a series of 100 or 200 mV steps. The Motronic handles this difference without a problem.

Going back to point 4) has given me the idea that by using an LC-1, I might be able to run without surge or hesitation or weakness at AFRs above the 13.8 to 14.2 that I've tested so far. Next I will try 14.7:1 (stock AFR) and then 15.2:1 to see how those mixtures run. Maybe we can "create" some more gas mileage for those who aren't interested in the power increase that 13.8:1 brings.

I will probably look at this some more next time I borrow a scope.

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