Hi guys,

I am looking to cut the 180km/h speed limit on my JDM '99 FD Type RS.
On this thread someone posted a photo where to cut the wire (for JDM cars) that transmits the speed signal - the ECU is located in the passenger foot area - see pic:



Unfortunately my cars seems to have a different ECU being a late model, see pic and logo - it's N3G1 instead of N3A7:



I installed a Knight Sports 300km/h odometer but it cuts at 180km/h.
There also seem to be far more wires than with the N3A7 ECU and they're all wrapped in blue, see pic attached (some blackbox is attached as well):





Any ideas how to get rid of the 180km/h speed cut here?

 

I can tell from a glance that someone's been in there and was "playing" around with things. The blue wires are an extension or adapter, see how they're epoxied into place in the bulkhead connector and the 3 connectors on the opposite side plug in? ECU wiring changed completely in 12/1995 when Mazda introduced Series 7 with the 16-bit N3Fx ECUs, so "cut this color wire" doesn't apply anymore. Different pinouts, different connectors, different wire colors, almost nothing is the same here. The vacuum system was completely redesigned too, I posted both diagrams in the 3rd Gen section.

I have the Japanese FD manuals & wiring diagrams which spell out everything, but it might be a bit before I can really dig into it due to prior commitments (20B Cosmo stuff). I'll take a quick look later today, it'll at least get you in the ballpark. However, based on all of this, I'm going to go out on a limb and say your car might not be a 99-spec. What's your VIN number? I can check it, but I have a sneaking suspicion you may be disappointed about how your car was misrepresented before purchase.

 

Hey mate, thanks for the input!
The car's VIN is FD3S-500***, so at least here I'm confident it is a true 99 model as I also bought it directly from a japanese car auction.

 

Yep, definitely built after 12/1998. As for the 180 km/h issue, these don't have an on/off switch input like the N3Ax ECUs. I took a quick look and Pin 4Q is Vehicle Speed Signal, conditions are as follows:
Source: Speedometer Sensor
Operating Conditions and Voltage:
Ignition Switch ON: goes from 0 to 4.0-5.0v
At Idle: 4.0-5.0v
When running: 2.0-2.5v

What to check in case of Malfunction:
Speedometer Sensor
Connectors and Harnesses between ECU Terminal 4Q and Speedometer Sensor

There is no mention of a speed-based change, since the input source was changed from the Combination Meter (N3Ax) to the Speed Sensor (N3Fx/Gx) directly. I believe the Speed Sensor puts out 12v Square wave and 4 pulses per revolution, but I could be mistaken about that. This is just a hypothesis, but it's possible that this pin sees a different voltage at 180 km/h than what is described, maybe something under 2.0v? Might be worth grabbing a voltmeter, jacking up the rear and seeing if the voltage changes from 2.0-2.5v to something else when you hit 180 km/h.

 

Get rid of that ECU and go aftermarket...problem solved

 

Thanks for the effort!
I checked and the car indeed does have a red/green cable that's responsible for the speed limit. Was somewhat "hidden" underneath the rest of the mess down there. Car runs free now - thank you very much! : )