• Overheated stepper ECU # 9684 ***

I connected a MAC pneumatic solenoid (rated 5.4W@12V measured resistance=... of the actual solenoid) to use with boost control just yesterday.

I connected it to stepper output A (L293D theoretically for min 25 Ohm = max 600mA continuous and 1A abs max peak load)

When it was time to use the solenoid it turned out it did nothing and would not actuate. I now discovered I had forgotten to invert the output to maintain normally open position, which meant it had drawn (measured) 0.5A all the time I had the ignition on. Solenoid was warm to the touch.

In addition, now the P259 low current outputs did not work either and I measured ECU current demand to 240 mA, so I moved relay functions to free injector outputs. ECU ign configuration is 6+2 so I had only two injector (or ign ?) outputs and used one for boost control solenoid and the other for fuel relay, the coolant fan relay we simply grounded the signal to the relay permanently to finish the tuning on the dyno.

The engine is a Toyota 1JZ with Hall sensor triggers and 4 passive coils. A really simple setup that uses a universal harness with solid ground in the welded roll cage (drift car).

Probably the +5V regulator on board is overloaded due to damaged circuits?

The car has run flawlessly last year, with manual boost pressure regulator.