4Mercedes.com 300CE Ignition Module Help! - PeachParts Mercedes-Benz Forum

Strife · #1 07-10-2006, 08:27 PM

Certainly, their function can be reverse-engineered (although how this would ever pass any pollution control board I don't know). Looks like an opportunity!

Strife · #2 07-10-2006, 08:44 PM

On a similar note, I bought a 420SEL module as an emergency spare for my 560. They apparently have very slightly different advance curves, but I'm hoping it will work if I need it (it might even work better...). All I can think of that could be going on in there is a big-a$$ transistor, a vacuum transducer, tach input (from the crank sensor), etc, and a CPU with a map of rpm-vacuum-ignition timing. MAYBE in that era this was done entirely with analog circuitry but I doubt it.

There is a guy on eBay who is selling a 3rd party (euro) version of a 380/500SEL (sl?) module, so cloning these modules apparently can be done.

As I see it, there can be two main electronic failure points in the thing, one obvious, one not-so-obvious:

1. High temperature, "wear-out", or possibly bad ignition wires or a coil can blow the output transistor. I thoroughly cleaned and sanded the bottom of my "new" module, and I will install it if I ever have to with heat sink compound (basically, what MB had on it in the first place). If it's misinstalled or if the compound gets old or washed away (from age, for example) the module may not be able to disappate heat into the body mount. Given the value of these things, If I ever need to replace one, I'll replace the coil and ignition wires preventatively.

2. More worrisome, the CPU inside may use one-time-programmable EPROM technology to store its programming; chips of that era generally were guaranteed by the manufacturer to store their programming only for 10-20 years or so. It would only take one bit out tens of thousands to cause a "checksum" fault and the entire thing would probably not work by design - potentially bad programming will automatically cause it not to run.