jumph4x

This is most definitely applicable to other Mercedes as well.

Took pictures for all you guys. Hope someone finds this, uses this and saves themselves time and frustration. Not to mention spare knock sensors.



I have one of the cars originally equipped with a bio-degradable harness, which was switched out specifically as it was being acquired by the owner before me. In the car now is a completely proper silicone\rubber isolating harness.

After getting my ECU chipped with an improper IC that it didn't much enjoy, I had to revamp the entire engine electrically and inevitably moved the said harness around.

Following this the car would develop a returning code P0327. The Bentley manual isn't much help here, but if you google this code you will see that it is almost always the wiring that is the culprit. On the cheaper designed GM cars its usually corrosion, but the Mercs are blessed with military style electrical connectors, so I had the tendency to disregard this. Our cars come with Siemens KS001 piezo-electric sensor that are rather high quality/.

Well, after replacing both the knock sensors, nothing changed.

Exhibit A: Sensor input harness connector at the ECU


Exhibit B: Your best friend when owning an old German car


One of the knock sensors was straight up turning up a SHORT. Yes, near zero ohm resistance type short. So I got under the car an disconnected the knock sensors and yanked the harness from the top so I had access. Stuck both probes into the 2 terminals at the connector. No short.

What? All I did was move the damn thing a bit. Oh... wait. You've got to be kidding me. Move the insulator around the connector end *BEEP*. Eff my life.

Lets take a looksie, shall we:

Exhibit C: ****ty connector design


What you are looking at is bare wire. Mercedes rely on the two wires being GLUED to the opposite sides oft he insulator for them to not touch. Wow.

Exhibit D: Insulation removed


Exhibit E: Connector exposed


See that?! I **** you not, I didn't strip a single millimeter of that wire. That is how long the bare sections are under the insulation. Mercs use some sort of a whack phosphorus coating between the copper or something. That green stuff crumbles out of there and wires short right at where they exit the silicone insulation.

I tried a number of solutions and this is the best I could come up with: separate the two wires and shown in the image and put a generous dab of super glue or Gorilla glue right in between them. Then electrical tape wrap the two individually, then together, then ziptie the assembly in multiple places. Underhood temperatures are highly unlikely to exceed 150F and the electrical tape is required to be tested to 80C, so you should be good on that front. Just make sure to use zipties that can take the temperature drops.

High quality shots available in my flickr bin: http://www.flickr.com/photos/jumph4x/

Other things to know:

• Work underneath the car, knock sensors are super accessible from the bottom
• The engine has multiple threaded holes, remember exactly the sensor locations
• Always use steel wool on the engine to clean that surface before reinstalling the sensor, it needs to be mirror flush
• 20 N-m is the torque rating on the bolts holding the sensors, don't overtighten
• Use anti-seize compound
• The military connector style is insulated with very soft\expensive silicone deep in the connector, theres no need to use any dielectric compound
• The size of the bolt on the sensors is 13mm

RANDY_P

Good one dude! Nice work.

rjp

jumph4x

Please rate the thread if you find it helpful!

MarcusF

It sounds like the replacement harness is bad too. Is it common for the second harness to get another shot at frying the ECU? Where do you guys buy your replacement harnesses?

jumph4x

This is pathetic though. I saw how its made and I'm not buying another one of these pieces of ****. I'll manually redo each terminal if I have to to get it straight.

This isnt the biodegradable one, so I'm keeping it.

hcetzneb

Nice work... That what i said in yor last thread its very common for the ends to do that..
the insulation decinagrates and than they short out... Its more common on the coil connectors, and injector connectors but ive seen it happen on all the connectors...
Heat, vibration are main causes ......... Fix the pins your self , alot cheaper new harrness cost about 1 grand.

hcetzneb

oh it affects alot everthing with a 104 eng / 119 eng and the v12 are the worse.

jumph4x

Dude, you're close. I live in West Hartford.

hcetzneb

Oh ya just noticed that .... Im in shelton area.

appatula

Happy ending!

That is just scary! Reminds me of my foglight connectors, I really wonder how many other "out-of-sight" connector wires are also prone to this. I suppose now when any codes come up it would be safe to check the harness going to that component thoroughly before buying the part.


Glad it all worked out and you've just donated some very valuable intel to the W202 community! Rated!





IM IN NEW HAVEN!


PS What kind of camera? Nice shots!

jumph4x

Tone is in the fingers Comparatively cheap Canon equipment: 350D body and the 1.8F 50mm prime.

Lets all meet up, eat seafood and take pictures.

jumph4x

Owner claimed he replaced the harness, but I'm no longer entirely sure about that. Perhaps he only replaced the squid going out to the engine?

Whatever the case, the whole thing is a piece of XXXX. I have more issues, this time on the ASR\CC\TB end of the harness. I am rebuilding this entire thing on my own.

Might be a little trickier than this: http://www.benzworld.org/forums/w140...oom-heres.html

Can't stand the electrical quality on this car. What a disaster.

DRBC43AMG

Checked out the thread on the other forum TOTAL DISASTER, but an excellent job done to get it back up and running

jumph4x

Will document it for you guys with photos. Will take a little bit to do this properly. Heres what I estimate this might take if I take my time with it:

• 1x evening to take it out
• 1x evening to do measurements, map colors and prepare the wire sections
• 1x evening to undo all connectors
• 1x evening of resoldering and re-wrapping
• [potentially] 1x evening to ring through the new loom with a multimeter going by the Bentley manual
• 1x evening to put it back in

I am starting as soon as my Bimmer is back from the transmission revamp (currently in for clutch, pressure plate, slave cylinder and all that jazz).

DRBC43AMG

Good luck on the work to do and keep us posted If this was done by a dealer, I can't imagine the final cost
Was/is the C43 plagued by the same ills?

MarcusF

No. All German manufacturers went through this. Bad harnesses started for some manufacturers in 1993 and some were bad through 1996. German government regulations called for biodegradable harnesses, or something like that. On a P car, even after the harness has been changed, some cars don't run right. That's because the bad harness can (nice way of saying "frequently does") short components and/or the ECU. With those cars, the fix is a new ECU and chasing bad sensors.

The C43 was introduced in late 1997 and I have never heard of their having a bad harness.

DRBC43AMG

Good to know that the C43 is safe from this type of "cancer"

jumph4x

Saab being at the forefront of this fxxkup pandemic. The year is 1985. Do not buy 1985 Saabs unless you like soy-based insulation.

taz069

Great write!! I am sorry not in the amg club but in the w202 club. I wish i could of found this thread earlier!! Not all my wiring is bad but most of the wires that hit certain connectors look like the above pics. I am currenttly trying to drive a 96 c280 with the m104 having same issues. Thanks again. And I hope this lil bump will help a few others!!!

DRBC43AMG

Both my fog light connectors looked like the photos before I fixed them. Luckily they worked and never shorted... So it looks like old age does also touches the 43