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Old 12-02-2008, 12:19 AM
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300EVIL 300EVIL is offline
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Join Date: Apr 2000
Location: Lake Geneva, WI.
Posts: 1,676
Originally Posted by duxthe1 View Post
Man, no sweat, I appreciate your input. The controller should very closely mimic an unaltered O2 sensor. The controller reads the O2 sensor digitally, decides to modify or not, and then outputs the new voltage through a MAX5354 DAC, once every repetition of the program. I havn't decided on maximum clock frequency yet, and have only simulated at ~125khz, but 8Mhz is theoreticly possible with the hardware I'm using. I'm going to determine clock frequncey once I can test it in operation.

I'm not too convinced that it'll need a wideband O2. Remember that I am getting a richer mixture by fooling the ECU leaner. Although I'll admit to not doing the math to figure out how much my 30% lambda ajustment will alter the mixture. FIgured it easier to measure it once I have it functional in the car. I'm lucky enough to have a gas analyzer at work. I know as an experienced mb tech that a car running at 20% lambda is pig rich. I'd expect peak power to have fallen off somewhere before 20%, though maybe not.

Don't forget that the controller is designed to lean out the mixture too. This idea was hatched back when gas was still near 4$ a gal. After a 14hr@4000RPM road trip last summer when gas won't cheap, I was really into the idea of being able to run lean on the long hauls.

Granted there are a lot of shortcomings compared to a stand alone EFI. My design goals were to keep it a simple interface that requires no other mods than to plug it in to the cig lighter and O2 sensor. Technicly, you won't even have to open the hood to use it. There's all sorts of tweaker gizmos for the EFI guys but almost nothing for us CIS-E tweakers. What I'm shooting for is a simple, easy to use interface that gives the CIS user control of the fuel mixture over most of the usable range of a/f mixture during closed loop.

Whether I pull it off or not remains to be seen but so far, so good.
I completely agree with your train of thought. It sounds like you did your homework and plugging in a piggyback controller between the O2 sensor and ECU would be a way simple mod to "trick" the ECU into performance mode.

However.... look at this. The factory ECU was designed to see a signal from the stock NBO2 sensor as is. If you have ever wired an LED meter to your stock O2 sensor (which I have....) you will notice the reading goes off the chart on a regular basis.

The only thing the ECU is looking for is what you can see on the LED display.

What you are proposing.... (for a legitimate performance gain) Will create a condition for the stock NBO2 to go "off the charts". If you leave it at this condition (what the ECU sees) for long enough the ECU will just look at the reading as being false and send the management into LHM and give you a CEL.

In my opinion, the factory ECU will see that the O2 sensor is "telling a lie" and ignore it. Never tried it myself but that's the "ECU logic" norm for what you are proposing.
Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320

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