Switched on Throttle

Introduction

We’ve added some new features for Our EA11R Cappuccino PNP, including variable throttle position sensor (TPS) support and an additional digital output for the Vaccum Switching Valve (VSV).

Throttle Position Sensor

The engine management system needs to know where the throttle is to conduct certain functions, such as enabling closed-loop idle, deceleration fuel cut, and acceleration enrichment.

Throttle Switches

The EA11R Cappuccino uses a series of switches for determining the position of the throttle. This was relatively common for Japanese cars at that time. The NA6 Miata used throttle switches, for example. These switches sense when the throttle is completely closed and when the throttle is completely open, but doesn’t otherwise communicate the state of the state of the throttle.

Variable Throttle Position Sensor

More modern systems incorporate a variable throttle position sensor. This communicates the position of the throttle continuously from fully closed to fully open. The engine management system uses this to sense fast changes in throttle position, which it can use to add and subtract fuel quickly, allowing for faster throttle response.

PNP functionality

Our PNP includes circuitry which interprets these throttle switches and outputs a signal which the microsquirt can read. This works surprisingly well in this application, even with large injectors. Even so, incorporating the ability to read a a variable TPS isn’t particularly difficult, so we included it in this board revision.

Variable TPS mode

A reference voltage is sent out on the IDL pin and the return TPS value is read on the WOT pin. The third pin of the throttle switches circuit is a ground reference at the ECU. These are the three connections required for a variable TPS.

To enable the variable TPS functionality, a series of solder jumpers must be opened on the PCB and a solder connection formed on the PCB. This will be added to the PNP manual before PNPs ship. If requested, KeiSport USA can ship a PNP in this mode. A variable TPS needs to be installed and wired in place of the throttle switches. The output of the variable TPS should be verified in TunerStudio and closed throttle and wide-open-throttle limits should be set.

Tuning

The acceleration enrichment settings for this tune are based on the response of the throttle switches. These will need to be retuned for the TPS.

Vacuum Switching Valve

The OEM ECU uses a VSV to control vacuum to the stock air bypass valve. We’ve included circuitry to drive this VSV and programmed it to respond appropriately. This can be repurposed for other uses, if desired.

Conclusion

It’s worth mentioning that there’s quite a more IO available on our PNP than this, including positions for an arduino, two CAN Bus circuits, and three UART circuits.