ECU HARNESS 6G72/6G74

Technical information, definitions, advice, and support for factory ECU remapping, aftermarket systems, and much more.
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Gus
Member
Posts: 15
Joined: 25 Mar 2019, 13:22
State: Western Australia
Model: TH
Engine: 3.5-Litre 6G74 V6 24V SOHC
Transmission: 5 Speed Manual

ECU HARNESS 6G72/6G74

Post by Gus » 24 Apr 2019, 13:34

I have a Manual Magna SPEEDWAY CAR with a 6G72 & Tin Computer , I am Changing Motor to a 6G74.

Can I plug the Plastic 6G74 Computer into the 6G72 harness ,

Are the pinouts the same to make the Engine Run ????

Are their any settings in the 6G74 computer that need altering

WytWun
Moderator
Posts: 567
Joined: 09 Apr 2011, 23:22
State: Australian Capital Territory
Model: Mitsubishi Magna TJ AWD
Engine: 3.5-Litre 6G74 V6 24V SOHC

Re: ECU HARNESS 6G72/6G74

Post by WytWun » 26 Apr 2019, 01:24

Gus wrote:
24 Apr 2019, 13:34
I have a Manual Magna SPEEDWAY CAR with a 6G72 & Tin Computer , I am Changing Motor to a 6G74.

Can I plug the Plastic 6G74 Computer into the 6G72 harness ,

Are the pinouts the same to make the Engine Run ????

Are their any settings in the 6G74 computer that need altering
As long as the harness connectors match the sockets on the ECU, the following are the only issues I'm aware of:

1) You will need to disable the immobiliser in the newer ECU.

2) If the harness is from an E/F series and the 6G74 ECU is from an H/J/L/W series, there will be no barometric pressure sensor in the MAF or the wiring in the harness to feed the sensor signal back to the ECU if you plug a later MAF in. In this situation a CEL will be raised for the missing sensor. If the ECU is from a J/L/W series the ECUFlash definitions support making changes to neutralise this CEL. Engine operation isn't affected either way.

Gus
Member
Posts: 15
Joined: 25 Mar 2019, 13:22
State: Western Australia
Model: TH
Engine: 3.5-Litre 6G74 V6 24V SOHC
Transmission: 5 Speed Manual

Re: ECU HARNESS 6G72/6G74

Post by Gus » 04 Dec 2019, 10:32

Have the car running & racing .... needs a bit more work.
The 6g72 harness has a plug near the LHF strut tower for timing & to check fuel pump voltage ..... the timing wire is apparently shorted to ground to take it back to basic timing

The 3.5 harness doesnt have this plug ...

So where do i set my spark timing & do i use this short to ground wire

WytWun
Moderator
Posts: 567
Joined: 09 Apr 2011, 23:22
State: Australian Capital Territory
Model: Mitsubishi Magna TJ AWD
Engine: 3.5-Litre 6G74 V6 24V SOHC

Re: ECU HARNESS 6G72/6G74

Post by WytWun » 05 Dec 2019, 20:58

Gus wrote:
04 Dec 2019, 10:32
Have the car running & racing .... needs a bit more work.
The 6g72 harness has a plug near the LHF strut tower for timing & to check fuel pump voltage ..... the timing wire is apparently shorted to ground to take it back to basic timing

The 3.5 harness doesnt have this plug ...

So where do i set my spark timing & do i use this short to ground wire
I believe the timing function you're talking about is actually for the purposes of setting the idle-air bleed screw (often known as putting the ECU into "BSS" mode) as the base ignition timing is set by the position of the CAS chopper plate and not the dizzy. The chopper plate isn't adjustable without modification as the fitting should be quite precise and not require adjustment unless something's been damaged.

From the J series (maybe H series) onwards you can only put the ECU into "BSS" mode through MUT commands. In the absence of a factory MUT system this can be done with an OpenPort cable and the Evoscan software which has a specific mode for "actuators" including the BSS function.

As I recall the base timing for the 6G72 is 15° BTDC and for the 6G74 it's 10° BTDC. Checking the timing with a timing light on a warmed up engine idling should show about these values even in the absence of BSS mode, though the value will jump around a bit as the ECU tries to maintain a fairly precise idle speed, unless the ECU ignition mapping has been modified.

If you need to remap the ignition timing used during normal operation you need to adjust the ignition timing map in the ECU, which is where ECUFlash+Openport cable and definition files come into play.

If you are trying to run a 6G74 with a 6G72 ECU (or vice versa) there are at least a couple of other ECU parameters that need to be modified in addition to timing, including:
- injector size
- MAF airflow (if MAF is different from the original ECU application)

As an aside: unfortunately in actuator mode Evoscan won't actually log anything :( so you can't maintain BSS mode and log the RPM to adjust the bleed screw - you need a separate tacho.

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