Early Mercedes Diesel Engine Instrumentation

[mach4]

Awhile back I embarked on a project to add engine instrumentation to my 380SL into which I swapped in a diesel engine. The stock gauges consist of oil pressure and temperature and I wanted something a bit more substantial. The goal was to add a variety of temperature sensors - oil, transmission, intake, TIT (turbine inlet temp) and engine bay, as well as pressures - vacuum and boost. Diesels don't develop vacuum, so the vacuum pressure being measured is from the vacuum pump which is used for brakes, door locks, shutoff and transmission modulation.

In designing the system, I didn't want any wires from the engine bay to the cabin and I wanted to use an old Android phone as the display so I decided to use bluetooth to connect the microprocessor and the display.

On the engine side, I used a Arduino microprocessor to collect and process the data and send it to the Android. The sensors included DS18B20 sensors for all the low temp sensors and a k-type thermocouple and a MAX31855 signal amplifier for the TIT. The boost pressure sensor is a 3-bar MAP sensor from a SAAB and the vacuum sensor is a 1-bar GM sensor.

On the display end, I'm using Processing as the programming language to create the displays. I actually have a library of 5 different displays to choose from which are selected by touching a button in the display and they scroll through. One digital display, three analog sweep gauges and one bar graph display. Others can be added at will by just adding a display routine.

Originally I just used an Android phone and a windshield suction cup holder but recently installed a larger display within the steering wheel itself.

Here is the Arduino setup



And the mounting in the engine bay



Here is the original display in use



And here's the new display mounted in the steering wheel horn pad.



Since the 380SL is a roadster, the tablet display is mounted with a ceramic magnet so it can be removed and stored when parked in an unsafe location.

As an '85 model, I don't have access to all the ODB stuff that the later model cars have, so this is a reasonable way to get additional performance data.

[Daox]

Very cool setup!

What has all the instrumentation taught you about the car?

[mach4]

Originally Posted by Daox

What has all the instrumentation taught you about the car?

Not a whole lot, but it's very nice to be able to monitor things like trans temp and TIT on long pulls uphill in the summer to really know that things aren't exceeding design temperatures. Monitoring boost lets me know how the engine is performing.

One thing I've learned is that my "cool air" intake setup is actually working pretty well. I'm within about 10 degrees of ambient for most situations. Monitoring TIT after a long pull lets me know when it's safe to shutdown the engine to prevent coking of the turbo.

Mostly it's there as an early warning system for things that are hard to troubleshoot without actual gauges.