Reverse engineering the Bosch K-Jet ignition module

The backstory

In early 2013 I have started the tedious process of collecting parts in preparation for the “nut and bolt” restoration of my low mileage 1979 450SE planned for the next 2+ years. To make my life easier, I have bought a mechanically sound, but rotten, 1978 350SE as a donor.

When dismantling the donor I have noticed that its ignition module (a.k.a EZL) casing was corroded beyond repair. Being a curious engineer, with some basic knowledge of analogue electronics, I have decided to donate the part to science in an attempt to reverse engineer the entire Bosch 0227100001B module. Curiosity was one motivating factor, OEM spare part cost at the dealership was another – at the time the module cost nearly 1000EUR!

Truth be told, these modules very rarely fail and there is no shortage of affordable second hand units on sites like eBay. So, why bother? Everybody likes a challenge! Hence, after about two years of very sporadic work on the project, the end result were two perfectly functioning prototypes, built using off-the-shelf components available at any respectable electronic parts supplier for under 50EUR in total.

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Installing rear speakers

I’ve finally gotten around to installing the rear speakers I got for Goldie about a year ago. Below is a short description of how I have installed a pair of Infiniti 5002ix 13cm speakers, without cutting or drilling any holes in the chassis. The only element that was modified was the parcel shelf, but in a way that – at least for me – looks great, and as if it were this way all along.

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About Goldilocks

Goldilocks (or Goldie), as ZV9485 is known in the family, is a late 1979, right-hand drive, UK delivered W116 series Mercedes-Benz 450SE. She is powered by a European, post-1978 specification M117 V8 motor with Bosch K-Jetronic fuel injection (M117.986). Power is transferred to rear wheels through a 722.001, 3-speed automatic transmission.

This particular car was manufactured around July of 1979, delivered and first registered in October of that year. The car came relatively well equipped from factory, with moss green velours interior, 14-inch light alloy wheels (“Bundt” design), power windows, power antenna, cruise control, headlight washers with wipers, and automatic sunroof.

As of July 2016, the car has been upgraded with 15-inch alloy “Bundt” replicas made by ARC, to improve handling and considerably increase the choice of high-quality tires. She’s currently rolling along on Dunlop Sport BluResponse 205/65R15, which are superb!

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For a UK imported car, ZV9485 was in a very good shape for its age when purchased by the current owner. There was no critical structural rust, it was mechanically sound with low, documented mileage and a great service history. The V8 engine needed no work whatsoever, neither burned or leaked oil, and was purring like a cat. The transmission was rebuilt ~10000 miles earlier.

The biggest rust issues were in all the common W116 hot-spots:

  • side members (sills),
  • the bottom part of both front doors,
  • top corners of trunk seal channel,
  • trunk floors,
  • under the hood in fuse-box and hood release cable corners.

It may sound like much, if you’re coming from Australia or California or some other dry area of the world, but for a UK/Irish car, this was a much better state than most W116 cars still on the road. Hence, the decision to restore ZV9485 fully was made.

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Brief history of the Mercedes-Benz W116

Source: Wikipedia

The ‘new’ S-class generation development began in 1966, which was only a year after the launch of the W108/09. This was the first Mercedes saloon to feature the brand new corporate styling theme which was to be continued until 1993 when the 190 was discontinued. The design, finalised in December 1969 was a dramatic leap forward, with more masculine lines that combined to create an elegant and sporty character. The basic design concept was actually inspired from the R107 SL-Class roadster, especially the front and rear lights.The car was presented in September 1972. The model range initially included two versions of the M110 engine (Straight-six with 2,746 cc displacement) – the 280S (using a Solex carburettor) and the 280SE (using Bosch D-Jetronic injection), plus the 350 SE, powered by the M116 engine (V8 with 3,499 cc displacement). Half a year later two new models powered by the M117 engine (V8 with 4,520 cc displacement) were added to the range – the 450SE and the 450SEL (with a 100 mm longer body).

The most notable W116 was the high-performance, limited-production 450 SEL 6.9, which was introduced in 1975, and became the first production car to use an electronic four-wheel multi-channel anti-lock braking system (ABS) as an option from 1978 on. This model boasted by far the largest engine installed in a post-war Mercedes-Benz (and any non-American production automobile) up to that time,  and also featured self-leveling hydro-pneumatic suspension.

The 300 SD sedan (American Market-only) had a turbocharged 3.0-litre I5 diesel engine developed from the C111 experimental vehicle.

The 450SEL was named the European Car of the Year in 1974.

Production totalled 473,035 units. The W116 was succeeded by the W126 S-Class in 1979. The W116 was sold throughout Europe, the Americas, Asia, the Middle East, Africa, and Australia.