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By RA.power
Hi everyone ,

I have an mx5 mk2.5 2005 1.8 vvt . I got a 0.4.3 (not VR Conditioner yet ) and test it with ardu-stim look that working fine. I am planning to turbocharge my car and I was thinking to do a piggyback setup the reason is I want most of the stock stuff to work "alternator control, fuel pump , radiator fan" without big drama. I ask in a FB group but they were very negative I don't really understand why. So my plan was to leave the stock ECU in place and give the speeduino all inputs from the sensors plus what needs extra and allow speeduino to control injectors and Ignition.

Any thoughts what can be a problem, what can't work as expected?
By SpartanSv
I did exactly what you plan to do on a Ford F-150 which also uses VR sensors. The only issue I had was with trying to share factory temp sensors. I just installed separate GM coolant and IAT sensors.
User avatar
I do not monitor the FB group (just here and Slack), so I'd have to ask exactly what the negativity was based-on. I don't like to guess, and someone may have a specific point. Alternator control is not difficult, and although it could be incorporated into Speeduino, it's not yet; and I've configured Nanos or ATTinys to provide MX-5 and other types of alternator control successfully. That said, piggybacking is popular to simplify the accessory controls, e.g., AC, cruise control, alternator, trans, etc.

From a technical point-of-view, piggybacking should generally require some PCB mods for signal sharing, by pulling the sensor input pull-ups and sharing grounds between ECMs. Calibrating is a bit more involved to calculate when sharing, due to the OEM pullup influence. Perhaps do a search on share or sharing sensors and piggybacks for some discussions and solutions. I can also post a step-by-step for shared sensor calibration if you go that direction.

By unBond
PSIG wrote: I can also post a step-by-step for shared sensor calibration if you go that direction.

that will be cool
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