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Discussion Starter #1
I had been having an intermitent misfire on cyls 5 and 2. the codes kept telling me that there was a problem with the coil pack for those cylinders. I finally found that I have an intermittent short inside the computer connector. I proved it by unplugging the connector and found that pusing or pulling on the wire bundle at the base, I can make it go from 0 to infinite resistance.

Last summer, I rebuilt the wiring harness, but I spliced into the original wiring just before the computer connector because the insulation was pristine and it still is. But now there is a short. I can't seem to get the connector apart easily and I am afraid to force it. Any ideas?

Thanks
Greg
 

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I remember that splice-in task G. Man, it sucks it inherited a connector short.

I've never played with that connector. Beware no one ever talks about replacement connector body, hood, pins or crimp tools. No doubt a factory assembly that may even be non-serviceable and heat sealed (welded).

Dude, I'd just bite the bullet and order the harness. If you go surgical and break it you just added down time.
 

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Can't help with the connector but I can tell you that shorting the coils can blow the output transistors in the ECU. Get it fixed asap.
 

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Discussion Starter #4
Cap'n and Whiteknuckles

The car is out of sevice until I get it fixed. I'm hoping that the ECU is still okay. This car has been nothing but problems. I even verified that the harness had been changed prior to purchasing it but the replacement was NOS so I am stuck with the problem I was trying to avoid. If I can't get a replacement connector, I will probably take the one I have apart and try to fix it at least to verify the operation of the ECU. I am loath to spend $900.00 for a new harness only to find that I then need to spend $2-3000.00 to get a new ECU. I will probably make a run to a u pull it and see if I can find at least another connector and hopefully another ECU.

Greg
 

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Discussion Starter #5 (Edited)
I called the dealer this afternoon. The parts lady said the part number for the connector is in the system, but none are in the US as they are special order from Germany. She said she would call me tomorrow and let me know price and availability.

I have heard that these connectors are the same for all 124s from 280s to 320s is this true?
 

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Discussion Starter #6
The connector PN is 000 545 53 81 and the cost is $18.93. They come form Germany and the shipping is 5-7 days. Needless to say, I placed an order.

Greg
 

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I agree with white knuckles...just bite the bullet and order a brand new OEM harness.

Just by the sound of it you're going to be chasing problems for the rest of the ownership of your car because of your "attempts" to repair the harness. You will most likely get teh most out of your car if you just buy one that's already made and is proven to work instead of trying to continuously chase down these issues you have by trying to fix it yourself, thus risking the chance of things like this happening...what could have been $900 might turn out to be $2-4k dollars...and if you want to risk learning the hard way like that then that's you. I don't see the logic in trying to fix it yourself when there are plenty of harnesses readily available, and are guaranteed to work.

And by the time you're probably done trying to repair your harness, you probably could have spent that money towards a premade harness, not to mention the time you waste trying to fix it, and the downtime of the car, is altogether worth the $900 itself...

Even then, I've seen brand new OEM harnesses go for as low as $650...you just have to look.
 

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Discussion Starter #8 (Edited)
chinny4290

I respect your opinion and the rest of this post may sound more harsh than I intend it to be, but I don't know how else to put it.

I fail to see how repairing a short in a connector is going to lead to chasing other problems that don't already exist. As far as I'm concerned, my repaired harness is light years ahead of what Mercedes saw fit to put into the car originally and even what they replaced it with back in 1998. Yes this car has been through two Mercedes wiring harnesses already. I have new wire from every sensor, the coil packs, and injectors back to within 18" of the ECU connector. The only giveaway that the harness I rebuilt is not original is that I used self amalgamating loom tape instead of the woven loom tape Mercedes used.

Wiring harnesses are not magic items. They are simply a bunch of wires that terminate in various connectors at various locations. As long as the wires go to and from where they are supposed to everything will work. If the replacement wires are of the same gauge and have equivalent or in this case much better (temp, bio resistance, etc) insulation, there will be no problem. My mistake was not replacing the ECU connector up front. Being in a hurry to get the car running and seeing that the insulation inside the battery well showed no signs of deterioration, I thought I could get away with splicing in.

In a previous life, I made a living building wiring harnesses for some very sophisticated computer controlled test equipment, much more so than this engine control scheme. I have also constructed them for racing vehicles and classic cars and even aircraft instrumentation on a homebuilt. I have a degree in Mechanical Engineering with certificates in motion control, PLC implementation, and electro-mechanics and automation. I believe that I am qualified to build a wiring harness.

If I have any problems going forward they will be because of the original failures of the Mercedes Benz OEM harnesses and not my replacement. I have absolutely no qualms about putting my technology in place of the crap that Mercedes engineers put into my car. Even now, the cause of my current failure is in the original section of a Mercedes replacement part.

I see this as a challenge and a part of the hobby. I thought others might have or have had the same opinion. I like fixing things and taking them apart to see how they work. This is how I learn. Buying the part when I know I have the skill set to build or repair it does not give the same level of satisfaction. I thought that someone ont is forum may have already dealt with this problem and may be able to give me some pointers. I also thought that someone else may benefit from my discovery that the connectors are available.

I have no problem spending the money, but, given the history of my car you can understand my reluctance. What I do not want to do is spend $900.00 then wait a few weeks to learn that I need to spend another $2-3K and wait several weeks before I can get back on the road. I would rather spend $20.00 and wait a few days then spend a few hours to find out that I need a replacement ECU and learn something along the way.

Thanks
Greg
 

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Discussion Starter #9 (Edited)
It's Alive!

The following is an update on the status of my 1993 300E 3.2L. The part I referenced earlier in this thread, PN 000 545 53 81 is only the outer shell of the computer connector, the pin body is only sold as part of a new wiring harness.

In order to fix the problem once and for all, I decided to replace every wire from the existing pin body to each sensor connector. I had to cut the old housing into several pieces to get it out of the way, but since I purchased two new ones I wasn't too worried.

The biggest hurdle at this point was removing the connector pins one at a time so I could solder in new wire. The pins are locked by two small tabs, the tabs can be depressed with something like a dental pick and the pin removed and associated wire can be pulled out for removal and new wire can be soldered in place. The pin and new wire can then simply be pushed back into the correct hole and the tabs will lock back in. I went slow and removed and repaired one wire at a time.

When I reinstalled the harness and started the car, I found that I still had a nasty miss. The diagnostic code told me that I had a problem with with the coil pack for cylinders 2&5. All three coil packs were brand new as of Sept of last year so I thought that this was a sign that my computer was fried. Out of desperation, I decided to swap coilpacks around and low and behold, suddenly cyls 3&4 had a bad coil pack and 2&5 were okay. It turns out that one of the the brand spanking new Bosch coils failed in less than 2000 miles. Luckily, I kept the old coil packs and replaced the failed unit with one of them and I was back in business.

I believe that the coil shorted first and that the short to ground caused the insulation to fail inside the potting material of the connector. Since the insulation I used in my repair was superior in temperature resistance, the remaining biodegradable insulation failed.

After action take aways:

When faced with a wiring harness failure and you decide to repair it yourself, make sure to replace all of the wire even if sections of the original looks pristine.

Don't assume that new or newly replaced parts are good.

W124 wiring harnesses are rebuildable if you take your time and use quality materials.

Thanks
Greg
 

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Can I send you my harness?

GDC - sounds like you might be able to start a cottage industry rebuilding harnesses...:)
 

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Discussion Starter #11
GDC - sounds like you might be able to start a cottage industry rebuilding harnesses...:)
I was considering that very thing. But until I can find a source for the various sensor connectors it is on hold.

Greg
 

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chinny4290

I respect your opinion and the rest of this post may sound more harsh than I intend it to be, but I don't know how else to put it.

I fail to see how repairing a short in a connector is going to lead to chasing other problems that don't already exist. As far as I'm concerned, my repaired harness is light years ahead of what Mercedes saw fit to put into the car originally and even what they replaced it with back in 1998. Yes this car has been through two Mercedes wiring harnesses already. I have new wire from every sensor, the coil packs, and injectors back to within 18" of the ECU connector. The only giveaway that the harness I rebuilt is not original is that I used self amalgamating loom tape instead of the woven loom tape Mercedes used.

Wiring harnesses are not magic items. They are simply a bunch of wires that terminate in various connectors at various locations. As long as the wires go to and from where they are supposed to everything will work. If the replacement wires are of the same gauge and have equivalent or in this case much better (temp, bio resistance, etc) insulation, there will be no problem. My mistake was not replacing the ECU connector up front. Being in a hurry to get the car running and seeing that the insulation inside the battery well showed no signs of deterioration, I thought I could get away with splicing in.

In a previous life, I made a living building wiring harnesses for some very sophisticated computer controlled test equipment, much more so than this engine control scheme. I have also constructed them for racing vehicles and classic cars and even aircraft instrumentation on a homebuilt. I have a degree in Mechanical Engineering with certificates in motion control, PLC implementation, and electro-mechanics and automation. I believe that I am qualified to build a wiring harness.

If I have any problems going forward they will be because of the original failures of the Mercedes Benz OEM harnesses and not my replacement. I have absolutely no qualms about putting my technology in place of the crap that Mercedes engineers put into my car. Even now, the cause of my current failure is in the original section of a Mercedes replacement part.

I see this as a challenge and a part of the hobby. I thought others might have or have had the same opinion. I like fixing things and taking them apart to see how they work. This is how I learn. Buying the part when I know I have the skill set to build or repair it does not give the same level of satisfaction. I thought that someone ont is forum may have already dealt with this problem and may be able to give me some pointers. I also thought that someone else may benefit from my discovery that the connectors are available.

I have no problem spending the money, but, given the history of my car you can understand my reluctance. What I do not want to do is spend $900.00 then wait a few weeks to learn that I need to spend another $2-3K and wait several weeks before I can get back on the road. I would rather spend $20.00 and wait a few days then spend a few hours to find out that I need a replacement ECU and learn something along the way.

Thanks
Greg
Dude... you have no idea how I can relate to that.

Props to ya, keep up the good work and great determination.

:bowdown:
 
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