First of all, keep in mind that this is a one-owner W210 with only 100,00 miles, with stock stereo and alarm and no broken electrical connectors or other evidence of tampering. An originla California car, bought new at MBZ of Palm Springs, it has no signs of rust or corrosion anywhere on the vehicle.

After reviewing the wire diagram, and consulting a W210 platform expert here at our firm, I discovered that power to the ECU is supplied by connector 'E' pin 5-6 of the K40 Relay. Fuse F4 (40amp Maxi) was hot vut (3) of the (5) 15amp fuses on the K40 were dead - clearly a bad K40, right???

Swapped in a known good K40 and instantly found voltage present at 'E' connector and fuses F-1 through F-6 were now energized. However, the car still cranked but would not start.

Ok, so we know now for a fact the K40 is bad, but what else is wrong???

I then checked the voltage signature and found the battery to be 12.72 and 'E' connector pins 5-6 AND Fuses F-1 through F-6 (excluding the F-4 maxi fuse) had only 8 volts!!!

A check of the wire diagram showed a multi-point ground in front of the ECU 'Nest' and it looked perfect, with no sign of moisture or corrosion. However, this ground had 190-200 ohms of resistance.

I took the blades off the stud and still no visible sign of corrosion. This car doesn't even have dust in the engine compartment, because it has always been (and still is) garage kept. However, once I treated each blade with dielectric grease the resistance value disappeared and both the 'E' connector and fuses registered battery voltage.

The M104 started immediately.

So, looking back over the past 30 days of ownership, my wife has complained about pushing the throttle at times with no acceleration and a bizarre intermittent 'misfire' or 'roughness' while idling at a traffic light.

2 weeks ago, I drove the car (for the first time) and noticed a slight misfire at idle with a corresponding 'puff-puff' in the exhaust. I also got a CEL and code for cylinder misfire. In response, I changed to a new set of OEM spec spark plugs and this problem seemed to go away. However, the more I think about it, the more I think the ground insulation and K-40 issues are the true cause of these anomolies.

The car always ran great, but it is noticeably smoother and more powerful now.

So, to the $3,000 purchase price of this W210, I now only have to add a brand new MBZ K40 Module for $147.95. What a blessing!!!!

Hope this helps someone with a similar issue...

Attached Thumbnails

       

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership