Tuesday, April 10, 2012

Stock engine management system

My car is old school and so the ECU doesn't have any standard way to be reflashed, there is no OBD connectivity, and it actually doesn't have an internal ignition timing map. That's done mechanically with springs and a vacuum actuator in the distributor (which PIT will not use). It's a weird mix of electronic goodness, and mechanical cleverness.

The stock engine management system is made up of two modules, an ECU (engine control unit) and a knock sensor unit. I wanted to get a better understanding of how they work, but couldn't find much information to start with. Perhaps my google-fu is not powerful enough, but there doesn't appear to be any publicly available information on the modules themselves. All i can figure is that the knock sensor was created by Mitsubishi, and the ECU by Denso.

Lets crack them open!
I started with the knock controller. Engine knock is an event that occurs in an engine cylinder where ignition occurs too early and/or in multiple locations causing turbulence which can knock the piston into the side of the cylinder wall instead of pushing it smoothly straight down.
Wikipedia: http://en.wikipedia.org/wiki/Engine_knocking. Sensing engine knock is a complex process which starts with taking audio input from a microphone or piezo sensor mounted on the engine and then isolating a specific sound frequency.

I was surprised by what I found, which was.. not much
The datasheet for the 2 ICs show that they're quad comparators. I expected to see a microcontroller or DSP! Underneath I found another PCB connected by a ribbon cable.
Unfortunately i couldn't remove it without damaging it. No way I could find a replacement and I still need my car to work in the mean time!

Not very interesting, so I decided to move onto the ECU.

I'm most interested in these two ICs. The one on the left looks like some sort of microcontroller, and the one on the right appears to be an EEPROM chip. Surprise, there is no data available for them. I can't even find a pinout. After much googling I found that yes, the one on the left is a microcontroller, but it's a proprietary Denso one. It was probably used in many cars during the 80's. Here http://forum.clubna-t.com/showthread.php?p=42205 I found that at least a few people have successfully hacked them.

"I hacked the Denso MCU a long time ago.
The above board runs the original factory code that is inside the original ECU.
If I leave the code stock (apart from a couple of essential byte changes to swap the mode and ensure the ROM checksum is OK) then the ECU runs exactly as stock.
It's possible to alter anything in the original program or the mapping."

So it seems that some clever people are able to do some interesting things with it, but that's beyond my capabilities. I at least got to learn a couple of things, which was really the whole point.