Hi guys,

I'm hoping the magna brains trust can help us out.

I'm part of a team that runs an off road buggy running a magna v6.
We had a 96 3L with auto (fully operational) with the immobiliser talking to the ecu.

The engine got a bit tied and we installed a 3.5L + auto (1999?).
Problems:
the immobiliser doesn't talk to the 3.5L ecu at all, did Mitsubishi change the immobiliser design?

when we run the 3.5L off the 3L ecu it runs badly...over fuels big time, however when you provide the motor an air leak in runs smoothly?

ideas?

Did you use the 3.5 injectors, I know in a Magna situation that these run fine on the 3.0 ecu running the 3.5 injectors.

The 3.5 ECU from the TH series onwards uses a BEM set up

Other alternative is get a J series ECU with the Immob switched off

cheers for the fast reply

Yeah the 3.5L engine itself hasn't been touched so still 3.5L injectors

my digging around the site suggests alot of people have run the 3L ecu on the 3.5L.
my thoughts are, we might just need to run it a while for the ecu to relearn the new motor (that seems to be the only issue related to a badly runign motor @ idle)

Have you checked the condition of the oxygen sensor? Running rich is the usual symptom of a dead O2 sensor. I mention this because in changing to a 3.5l engine, the injectors have a 25% higher flow rate for a 17% increase in displacement. Adjusting for this would be within normal tolerances for the ECU fuel trims, allowing the 3l ECU to run the 3.5l satisfactorily as MadMagna indicates. However a dead O2 sensor in this configuration could result in significant over-fuelling as you report (with a 3.5l ECU it would just result in running quite rich but not usually to the point of running badly).

The immobiliser function in the 3.5l ECU would need to be disabled. If that ECU came with the 1999 engine/trans, this is possible with access to an OpenPort cable and the necessary wiring in the loom connection to the ECU. If you want to learn more about this, see the thread linked below.