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Help with building your Speeduino, installing it, getting it to run etc.
By Kunundrum
Hi Folks,

Has anyone successfully piggybacked a Speeduino on an OE PCM ?

So the PCM would think it's running the engine, but in reality the Speeduino would be, and all the PCM would need to see is crank and coolant temp to stay happy, and those are easy enough to split between the two.

thoughts ?
By theonewithin
Been done hundreds of times.

No different to piggy backing using any other ECU.

Just google "how to piggy back ECU megasquirt" as a starting point
User avatar
By Chris Wolfson
You should write what kind of OEM System you want to run this way. If it is an old system, like OBD I, you sure can do it.

With later generations this will get harder or impossible, as these double check anything they do and have to many regulating loops that detect any difference from the pre-set targets, while constantly adapting to any change. So if Speeduino rules the engine, you will get all kinds of error messages in the OEM system. For example, just a difference of a few rpm from the value the stock ECU decided to run will be recognized as an error.

A Speeduino is a very good ECU for running an engine with best performance and economy, if mapped right. It is as far developed as a very good mid or end 80's ECU system, just much cheaper, with much advanced components and perfectly programmable. The great advantage of Speeduino are modern sensors and the Software running at the PC tuning it.
Not only with gasoline direct injection things get ugly. In no way is it a match for any of today's ECU's, that have hundreds of maps to run engines with hardly measure able emissions.
In many of the worlds mega cities, the exhaust emission of a last generation gasoline car are cleaner and less poisonous than the air that entered the engine, except for oxygen missing. You can not realize that with a simple Speeduino. Speeduino does no kind of adaptation and the most sophisticated function so far is some kind of VANOS.
In a modern ECU anything is controlled, from fuel and (!) oil pressure, selective cylinder cut off to cooling temperature and water pump speed. Basically even the cars most remote functions are connected to the engine and can influence it.

So, what do you have?
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