vems v3.8 installed on mx5 nb vvt with cam sync
using 36-2 crank trigger wheel to allow better sync
cam sync modifed to one tooth to allow correct sync angle for vvt
wiring ... TODO: wiring list (as much detail as possible), especially EC36/23, outputs, and grounds.
P259 output flyback
- 6 of the P259 outputs (EC36/pin 3,4,15,16,30,31) have SMB (surface mounted) diode flyback protection (at the bottom of the board, between EC36 and PCB edge) with the common cathode connected to EC36/23 flyback
- 2 of the P259 outputs are only available internally, not on EC36 or EC18 connectors, they do NOT have flyback diodes. (these "outputs" are not normally used anyway).
We '''suspect that something in the harness erroneously pulls down EC36/23 flyback to GND (possibly intermittently). That, via the flyback protection diodes of the p259 outputs can cause apparent activation of the outputs (pull down to appr. 0.6V that is almost same as if p259 activates the outputs... distinguishable with careful measurement, but it will certainly activate a relay, or warning light or LED).
Maybe one injector is shorted? Or the harness has some short?
Is the EC36/23 flyback connected to the injector common +12V ?
Perhaps EC36/23 is not powered properly (usually involving a fuse and a relay) from +12V, and pulled down through some load (eg. relay or injector), not shorted to GND, but enough to cause apparent activation of the p259 outputs (via the protection diodes?)
EC36/23 flyback must be checked carefully.
- Is the +12V stable there when ignition is ON?
- How are the injectors powered?
P259 outputs - P259 outputs work, no indication of any problems. (2026-03-01)
- NOTE: this was first "remote" hint, not directly applicable, since p259 was found to be working well.
- The most likely cause of "p259" (=TPIC6A259) chip failure is insufficient ground connections.
- Please check GenBoard/Manual/GroundConnections (With good connections and no overload the chip will likely to work 30+ years. However, failing to fix the root cause will likely result in damaging the p259 chip, possibly again and again). It is best to use spare injector outputs, or spare power-IGBT (ignition) outputs to drive relays, solenoids, and only use p259 for warning light, LEDs (with series resistor) and similar signals.
- The most likely cause of "p259" (=TPIC6A259) chip failure is insufficient ground connections.
The car has a custom wiring loom for the engine. The original car loom has been spliced in to the ecu for the original gauges to work
Alternator control
The alternator is normally ecu controlled however I've fitted an aftermarket alternator controller board this is wired to the ecu to disable the alternator on startup and used on high tps to get more power
http://www.vems.hu/files/lewisw%20mx5%20nb/v3.3_u023257-A-2026.01.24-16.08.32.vemscfg
this is the lastest config at the point of write up. the car is up and running but not mapped yet