Quote:
Originally Posted by niky
As for buying a piggyback for fuel economy, you have to do a lot of research. Many cars will "relearn" around a piggyback, adapting to the change in fueling parameters by altering the fuel maps over time. Which means you need an O2 sensor intercept, which will cost extra.
And the amount of money spent on a piggyback will often not be recovered through fuel savings. A piggyback that works properly costs a bit of money, as do the dyno-tuning or street-tuning required to get best performance (alternatively, you could tune it yourself, but that means spending more money on a wideband O2 and software).
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An older car wouldn't really adapt to the piggyback, with narrowband O2 sensors, no EGT sensors, and open/closed loop based off rpm the ECU is easily fooled.
For fuel economy increasing I don't think the tuning would be that difficult especially if you can use a switchable map (not that I'm saying this is easy to get in most cases) and use a wideband input. You can erase some of the emissions safety margin built into the top of the powerband by leaning it out to a more reasonable 0.85 lambda instead of the 0.75-0.8 on a lot of stock cars, and then lean out the cells in your cruising range to 1.2 lambda, and tweak the spark advance just a bit (since you're changing the low load cells there's already a lot of advance).
If you drive a lot of highway miles like many people in the US, the 5-10% fuel you'd save doing that could pay off the piggyback in under 2 years. A Greddy EMU is what, $800-900 with a harness? Unichips are less but I don't know if they're as capable. I think the EMU can run the injectors independently using a wideband input, and you can use a narrowband emulator to get the stock ECU to cooperate, since the stock ECU would then have no idea what the injectors are doing at all. A gas guzzler SUV/truck/luxury land yacht burns through several k in fuel in a year easily.