Evo 5 rallycar: Can I replace my GEMS ECU with an OEM ECU?

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Evo 5 rallycar: Can I replace my GEMS ECU with an OEM ECU?

Post by Bugster » Sat Sep 20, 2014 10:34 am


I am new to Evos, and pretty new to engine management systems. I recently bought a -98 Evo 5 RS rallycar. Left hand drive and in pretty good shape. It is currently mapped for racefuel and runs very well, allthough pretty rich. But I assume that is quite normal for a rally car built for going full throttle through the woods. I would like to have it registered for road use. That means I need to put it back to stock to get it approved by the Norwegian road/car authorities.

I took out the ECU last night and opened it up. A yellow sticker on the eeprom inside says LANCER7 G2.41.

I would like to keep the GEMS ECU for later trackday use.
Is it possible to buy a JDM original and unmodified ECU from an EVO 5 or 6 at the breakers yard, plug it in, replace racefuel with ordinary fuel and make it run like stock?

If not, what else needs to be done?

Thanks in advance. :)

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Re: Evo 5 rallycar: Can I replace my GEMS ECU with an OEM EC

Post by RickS » Mon Sep 22, 2014 3:35 pm

Well that's a first..! Usually the swap is the other way around.....

I don't think that the swap back to OEM will be that straight forward. I suspect that the injectors may have changed for one thing, so they will probably flow too much fuel, even when the 'stock' pulse width is restored. Having said that, the stock injectors were good for 300 h.p. so you may be lucky.

Spark plugs will probably be aftermarket (temperature) and it would be worth checking to see if the load sensor (either MAP of MAF) may be different from stock. Hard for me to diagnose without looking at it but as far as the connectors are concerned, you should jest be able to plug the OEM ECU straight onto the loom.

One thing that GEMS would have recommended when the conversion FROM stock to our ECU was carried out, is that pin D17 was used for ALS rather than the TPS switch for which it was designed, so that's worth checking over.

Best regards,

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