Incendiary 124 (tediously long post)

[nmacc]

Hi folks,

I'd been having some very rough-running problems for a while, but couldn't track them down because the problem was intermittent.

It turned out to be caused by perished insulation on the leads to the MAF, as you can see:

Subsequently I removed the MAF connector. Since it's moulded on I had to saw off the top, but as you can see, the insulation failure goes all the way to the pins:

Anyway, on Saturday I called to a local independent MB specialist to see if they could read the codes. Instead the mechanic moved the MAF wiring and the engine ran smoothly. Excellent!

So I moved the MAF wiring, and the loom went up in smoke! Now I have a bigger problem:

It's also quite possible that all of that melted insulation has resulted in a blown ECU, but I won't know that until I've made some sense of the charcoal.

I've begun the rebuild, but I've reached a tricky point. Although I've reconnected most of the damaged cables, I'm left with four red/blue wires. Actually two are red with a blue trace and two blue with a red trace; at least that's how it looks to me.

Two of these definitely went to the OVR; pin 6 I think, but I'm not sure where they went from there. One of the free ends in the loom goes (I think) to pin 38 on the ECU.

Also, there was a 2-pin connector supplying power and ground to the MAF. There's not much left, but I suspect that the power was on one of the blue/red leads.

What I'm getting at is, does anyone know if all of these blue/red leads are electrically identical? If so, I should be able to connect them together.

Of course the ultimate resource is a diagram of the engine loom. The Haynes manual is quite good in this respect, unfortunately it doesn't cover the 220.

Any assistance would be much appreciated.

Thanks,

N.

 

[grober]

MAYBE THIS WILL HELP its from the C class manual 3511 by HAYNES

 

[bolide]

Try this (requires membership):

http://www.service-and-parts.net/dcagportal/DCAGPortal/portal.action

Nick Froome
www.w124.co.uk

 

[nmacc]

Thanks to Graeme for the diagram.

Although it's not my engine (no OVR relay), it does show 2 blue/red wires in use. One being the ignition feed to the MAF and the other being from the ECU to the fuel pump relay. Which makes sense, you don't want the fuel pump relay permanently energised if the motor is not running. Just a case of getting the wires correct.

Nick, many thanks for the link; I registered and paid €19 for EPC and WIS. Unfortunately, try as I might, I can't seem to find any circuit diagrams. I'm not entirely sure what I signed up for as there were two time periods listed: 1 hour and 1 year. I'm guessing that means a total of 1 hour's access valid for one year. For this reason I'm reluctant to stay on line trying sections at random in the hope of finding a circuit diagram.

Could you, or anyone else with the experience of this system, help with a few suggestions as to where I might look?

Thanks.

 

[Vlad]

If you need a replacement ECU I have one from my E220 that I scrapped earlier in the year...perfect example, but as you may know there are a number of different ECU's for the 220 depending on the options fitted to your car, ie auto/manual, air-con, or no air con etc etc.

If you need it, let me know what part number is on the side of yours and what options you have on your car.

 

[nmacc]

Thanks Vlad, I may have to take you up on that. I'll get back to you with the number.

I should be in a position to try starting it later today, but I'm still a little stuck on the red/blue wire problem. I'll let you know how I get on, but I'll definitely have a fire extinguisher handy when I connect the battery!

 

[nmacc]

The ECU is: 013 545 07 32 [00]
It also bears the details: HM 0001 HM 2.2l 4-cyl

I'm not at the car at the moment as it's still at the garage, I dragged those details off a photo I took of the ashes, so that's the MB number, the Bosch number is obscured. I'm off down to the garage in a moment, so I'll have the Bosch number later, if it helps.

Thanks again.

 

[nmacc]

Success!

Elle Va! (as the French might say).

Thanks to everyone for all the help.

She starts; she runs. Frankly no-one was more surprised than I was. There was a large number of stray wires to be rounded up and terminated, which is nigh-on impossible without a circuit diagram.

I must offer special thanks to Graeme for his posting of the C class diagram. Although it only helped me route one wire, it was absolutely vital as the presence of severed red wires with a blue trace and blue wires with a red trace would have scuppered me without that help.

It took a couple of false starts as I had one pair of wires reversed on the OVR and I had the polarity of the sensor part of the MAF wiring reversed - what idiot would design a device that was polarity-sensitive, yet was wired with one wire green with a bright yellow stripe and the other green with a pale yellow stripe?

I still have a lot of work to do as I now have a running car with a loose pile of relays, modules and controllers in a heap behind the battery. Not to mention a horrible mess of mis-matched wiring held together with choc-bloc connectors, insulating tape and a few bits of heat-shrink that finally arrived today when most of the work was done. At least it's now in my driveway and not in the garage forecourt.

I'm not absolutely convinced that 100% of the wires are where they should be, so if anyone has a circuit diagram of the 220 engine harness I'd still be most grateful.

Thanks again and finally apologies if I should have started this thread in the Electronics section.

 

[grober]

Result! Least its a runner now.