Fooling OBD-2

[big_papa_pump]

Is ther a way to keep the OBD-2 computer from adding extra fuel??? I'm hoping there is a work around for the second O2 sensor that makes the computer think that everything is normal, eventhough its not hooked up. I just want a more consistant fuel mix for when I install and tune a VAFC later, and not have to wory about the computer adjusting for it. (By the way, Kansas has no emssions testing)

[fritz_269]

You're trying to run in open-loop mode all the time?

Why!?! The O2 sensor and closed-loop fuel control is a great technological advantage: You'll get more torque, less detonation, better throttle response, and more MPG.

Don't ditch it on a whim.

It can be done though (I still don't know why) - just purchase an upscale aftermarket ECU (like a motec M4) and build the fuel maps on a dyno with a wideband O2 and and EGT sensor. (See, you still need an O2 sensor to tune it!)

[big_papa_pump]

I still plan on keeping the primary O2 sensor (the one on the header), I was wondering about the second one (the one on the converter). I was thinking along the lines of a false signal to the ECU, making the computer think that the converter was functioning an optimum level. Kind of like immitating the voltage of a properly functioning converter, so the OBD-2 won't increase the fuel ratio... I know an OBD-1 conversion would be easier, but I can't really afford the conversion. Will ATTS even work with a different ECU (OBD-1)???

[drift]

you can "disable" the second O2 sensor with this:

http://www.importparts.com/importpar.../catalogs/1353


as for the ECU, ATTS is built partially, if not wholly into the ECU, if i'm not mistaken. i know there is a separate ATTS controller, but i think it must function in tandem with the ATTS equipped ECU. thus only a 1997+ SH ecu only

[big_papa_pump]

Thanks Drift, thats exactly the kind of thing I was looking for!! Do you know how well it works on Honda's though??? As for the ECU, as I understand it the ATTS computer ties in to the ECU for a couple of sensor readings but functions independently. I've asked about it at a couple of shops around here but no one knows for sure.

[RunninSOHC]

If you're trying to gut the cat you nice Prelude is gonna make a Rattle from 3 grand up. If that's why you want to disable the o2 you should really reconsider because that will make a pre ghetto

[big_papa_pump]

Actually I have a Randon Tech high flow cat, no rattles.

[fritz_269]

Originally posted by big_papa_pump
I still plan on keeping the primary O2 sensor (the one on the header), I was wondering about the second one (the one on the converter). I was thinking along the lines of a false signal to the ECU, making the computer think that the converter was functioning an optimum level. Kind of like immitating the voltage of a properly functioning converter, so the OBD-2 won't increase the fuel ratio... I know an OBD-1 conversion would be easier, but I can't really afford the conversion. Will ATTS even work with a different ECU (OBD-1)???

I'm sorry, I misunderstood. :o

Basically, the 2nd O2 sensor is there to make sure the cat is doing it's job. There should be less free O2 at the end of the cat than at the front - so the second O2 sensor just needs to read a little lower than the first one to correctly fool the ECU.

The box drift posted may well do the trick, although I've never actually seen one. I have also seen a simple resistive divider work too - but that might be a little more flaky (but cheap!)

Question - If you're keeping a cat - why not just add the 2nd O2 sensor back into its original place?

[drift]

Originally posted by RunninSOHC
If you're trying to gut the cat you nice Prelude is gonna make a Rattle from 3 grand up.

it's rattling because you did something wrong, like forget to attach an exhaust hanger or something.

[drift]

Originally posted by big_papa_pump
Thanks Drift, thats exactly the kind of thing I was looking for!! Do you know how well it works on Honda's though???

it should work just fine... just pure assumption would lead me to believe that it's a simple resistor that keeps the O2 sensor sending exactly .5 volts back to the ECU, effectively telling the ECU that it's running stoich.