E28 5-Series 528e with the Eta (not Super Eta) engine ECU Design Difference

If you like, you can skip directly to where you can buy this part

I have owned a 1988 528e, and a 1985 528e, and I wish I’d paid more attention to these cars’ differences, specific to the fuel injection. Because I didn’t, my information as such is, sadly, hearsay or second-hand — albeit from sources that I choose carefully.

The Bosch fuel injection used by the E28 528e fits the style and structure of the L-Jetronic type of fuel injection. It has an air flow meter with a swinging vane, it has pulsed fuel injection, it has an ECU and so on. What is new, on top of the fuel injection, is integrated computer-based control over the ignition aspect, too. Hence the name “Motronic” to describe this system, no longer “Jetronic.”

Wikipedia has a nice analysis that reconciles with what I have seen.  Here is an excerpt from their write-up.

Main system characteristics
  • Fuel delivery, ignition timing, and dwell angle incorporated into the same control unit.
  • Crank position and engine speed is determined by a pair of sensors reading from the flywheel.
  • Separate constant idle speed system monitors and regulates base idle speed settings.
  • 5th injector is used to provide extra fuel enrichment during different cold-start conditions. (in some configurations)
  • Depending on application and version, an oxygen sensor may be fitted (the system was originally designed for leaded fuel).

The first version of Motronic was named, aptly, 1.0 and it was used in the E28 528e models with years 1982 through 1987. For 1988, BMW made several changes to the E28 528e model. I’ve pieced together the story mostly based on the adventures of someone who tried to retrofit 1988 goodies onto an earlier model. What seemed like it might be a simple task was actually very complex.

The 1988 model has Motronic 1.1 and there is much, much more involved than swapping out the ECU. The way the system senses the position of the engine is, for example, different.  The wiring harness is different.  The engine also has, as I recall, the head from the “i” engine. Wikipedia also mentions that the pistons were different. The result was nicknamed “super eta” whereas the previous years’ models’ engine was the “eta.”  According to Wikipedia, it was more powerful by 6 horsepower, 121 vs. 127.

So, if you are buying the Motronic 1.1 unit for your 1988, great.  If you’re buying it to make a fire-breathing monster out of your pre-1988 car … maybe that’s not such a good idea. 🙂

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