PeachParts Mercedes-Benz Forum - View Single Post

duxthe1 · #29 12-13-2019, 08:57 PM

I've gotten back into this project and today was going to be a big day for me. I managed to buy a 500 SL module and it was delivered today. After comparing wiring diagrams and confirming all of the major functions are present on the same pins, I've been real keen to get my hands on one. It didn't take long after getting in for the evening to open the box and unscrew the cover from the module. This is where my hopes were dashed. Despite a very similar pinout (the connector even plugs in without issue) the circuit board is wholesale different, and there is no 27c256 eprom to remove and read. There are two SMT chips at either corner of the board with shriveled part# stickers, likely where the program resides for this module.

This is a huge disappointment for me because there are a few subtle differences in the function of the 119 module v/s the 104 module and being able to find them in the code would have given me a big leg up on changing the idle speed as well as EHA control. Given that there is an additional tach pulse per revolution, the idle control code would have to account for that and that would have pointed exactly to where in the code the idle timer target resides. The 119 has about 75mA of key on engine off EHA current v/s the 104's (and 103's) 20mA. Finding that difference in the code would have been big too.

Another disappointing consideration is that this 119 module has WOT enrichment. I wasn't sure it would but I confirmed that it does by installing it and going for a spin. A few things I noticed running the 119 module on my 104. First off, check engine light. I didn't read codes but there are a few superficial differences and they immediately set a C/E light. Idle speed is high because time between tach pulses is long from the 119 module's perspective. Cam timing switchover is late for the same reason but gives a noticeable surge of power when it does finally come on. WOT enrichement is also noticeable and only makes me more determined to get it working in the 6 cyl code. The 75 mA KOEO EHA current is too rich and floods the engine when you crank it. You have to give it a bit of throttle to clear it enough to start.

At this point its back to the drawing board. This 500 SL module is 011 545 23 32. There are a few other numbers that could be valid, likely the difference between years and federal or California version. I'd love to get a look inside of a 008 545 77 32 and just to make sure there wasn't an early version based on the familiar 6 cyl board..