I have an S5 Turbo II JDM conversion. I have removed the emissions and still have a rich condition. In running through some diagnostics, I noticed that my 5th gear switch is reading 12 volts in 5th gear and reverse AND 1st through fourth. I am using an N370 Engine control unit. Someone told me that the JDM transmission does not use an 5th gear switch. I am wondering if this is changing the fuel injection timing so as to cause a rich condItion. Any Gurus out there? Am I better to leave the switch disconnected from the control unit?

 

So you transferred a 5th gear switch over to a jspec transmission? The N370 ECU will expect to see a 5th gear switch, but it's not a big deal if it doesn't. The switch serves 2 purposes: to allow the split air solenoid to open in 5th gear (useless w/out emissions equipment), and keep the shift up light from coming on in 5th gear. You can use a jspec reverse-only switch or disconnect the 5th gear side of yours with no consequence, but there are no fuel/timing changes with the switch active.

 

On a series four USA car, the fifth grear or over the top switch is used to put a ground on the split air solenoid of the ACV to inject a small amount of air to the converter.

On a series four car you can just turn the key ON, engine OFF and select fifth gear and hear the Split air solenoid of the ACV go......click. Not really good for much of anything. JDM cars don't have a fifth gear of over the top switch at all. That solenoid does not exist on the JDM ACV if memory serves.

I'm sure series five are similar.

The post above this one was made while I was typing.