Wiring Loom

[Scop]

Just wondering how many people out there with E280 and 320 W124s have had to have their wiring looms replaced ?

 

[turnipsock]

http://forums.mercedesclub.org.uk/showthread.php?t=19083

one or two...

 

[kth286]

Scop

The starting signal for impending failure is when one of the three coils above the spark plugs start to blow, leaving the car firing on 4 cylinders instead of 6.
Whilst it is easy to replace a coil, you need to gently cut open the outer insulation of the wires going to the affected coil. You will likely find the insulation cracked inside, and the two wires contained therein will short and cause the coil to fail.

Be warned, if you do not fix (by replacing the loom is best long term solution in my opinion) asap you risk blowing the main computer. You now need a loom and a computer - megga bucks especially if you get someone else to fix it.
I would suggest that everyone with this engine budgets for a new loom - approx £600 in round figures plus labour on top.

I replaced my own and you can do it steadily over the course of a day.

I think Merc labour is charged at 3 hours - £300.

Note that everytime the spark plugs are changed the coil wires will need to be moved and this causes the hardened insulation to crack.

Hope that helps you avoid the problems.

Regards

 

[Scop]

Thanks for the replies. So far I don't have any symptoms apart from the warning light for a blown bulb coming on occasionally (lights working fine). The reason I asked the question was that i read somewhere that its not so much of an issue in this country due to our climate. I was just wondering how common it really is as I have just splashed out 850 on the head gasket and could do with a few months to rebuild the car fund !

 

[big x]

Just wondering how many people out there with E280 and 320 W124s have had to have their wiring looms replaced ?

My E320 94 103k saloon is on the original loom although it's possible the ignition leads have been replaced at some point.
I suppose the question should be has anyone got a high mileage E280/320 in this country with the original loom ? ? ?
In this hot weather I've not been using the car,I'm sure heat accelerates the breakdown process.

http://www.mercedesshop.com/Wikka/M104WireHarness

adam

 

[kth286]

Scop

I can assure you if you have the original engine wiring loom and you have now had a head gasket replaced, expect misfires in the near future (coil/s blown) depending how many miles you do.

That is because there is A LOT of moving around of the brittle coil leads when a ahead gasket is done.

A specialist worth his salt, should have warned you of that.

The professionals in the states do.

How many miles has your car done ????????

I am not trying to be alarmist, just realistic.

The least you can do is carry a spare coil in the car with you, which can be replaced quickly and easily with minimal tools to get you home if you are far away. About £45.

Regards

 

[turnipsock]

My loom went around 170k. I was putting in some helicoils, to hold the cover on, when I noticed some bits of insulation falling off.

The problem is that wires run through a hot part and the insulation becomes brittle. It may hold for a long time, but it's the moving around that will do the damage. Specialists will know the problem and be careful when working in that area.

 

[Hanz]

Yes, I've had mine repaired on my E280. Ended up blowing the ECU.... Mine has 191,000 on the clock. As you can see from the thread Turnipsock included

 

[Scop]

Many thanks for your replies and advice. I suppose I'd better get saving then !

 

[golfcarmad]

just had my ecu of C280 checked after car runs on 4 of 6 cylinders-no fault.Just uncovered wiring loom,i've never seen so much crazy paving in my life,its anightmare!!!!

 

[big x]

just had my ecu of C280 checked after car runs on 4 of 6 cylinders-no fault.Just uncovered wiring loom,i've never seen so much crazy paving in my life,its anightmare!!!!

So IL6 C-classes suffer as well.....any chance of a pic?

adam

 

[golfcarmad]

when it stops raining I'll do that-Ihave built dozens of race cars over the years (m inis mainly) and driven some right sheds in my time-but this harness is the worst I have ever seen.

 

[golfcarmad]

phots as asked for-not brilliant clarity but look closely,the red wire is very thick ad is cracked every 2 cms,most of the smaller ones are cracked every centimetre!!!!

 

[3146bj]

Replaced the loom in mine about 2 years ago just after the head gasket was done. The insulation on every wire in the cam valley was like coarse powder - you could blow it away! Every wire in the engine bay had failed to a greater or lesser extent. Probably worse here with high ambient temperatures resulting in very high engine bay temperatures.

There really is no excuse if our common old Holdens and Fords can go for 20 or 30 years without a problem in this area yet Mercede and Volvo (I've had the same experience with both) cannot make a loom to last more than 10-12 years. Perhaps some accelerateed testing is needed rather than leaving it to the customers to do the development?

 

[golfcarmad]

where/how much was replacement loom please?

 

[golfcarmad]

can i ask anyone whom has replaced a loom themselves,did it fix the problem imediately???

 

[turnipsock]

can i ask anyone whom has replaced a loom themselves,did it fix the problem imediately???

I spotted the problem so I never started the car before I replaced the loom.

If the loom was shorting out, you may have a damaged ECU. Either way, you will have to fix the loom first.

They are around the £500 mark and are fairly easy to repace yourself.

There is a lot of threads about this subject. One had pictures of a repair. It's only the bit that runs along the top of the engine that seems affected but when you have to replace that, you have to replace a whole lot more!

 

[golfcarmad]

Thanks,had ecu tested-told ok by ECU doctor on sth coast.Car runs ok on 4 x cylinders and LPG so might just keep using it for now.I have cjecked that current is going to coil,it just will not fire on 1 & 6 cylinders.If you look back in thread,i posted pics of loom as is-its an unbeleivable mess,every single wire is cracked every 2-4 cms.I am just concrned that I buy a new loom (535 + vat) and it does not fix the damn thing? tks for all advice PaulK

 

[124coupe]

Best to swap the loom and then read, note and reset the fault codes.

If the cyl pair still doesn't fire then we can help with fuel or spark diagnosis, knowing that there is no longer signal and/or 12V shorting going on in the loom.

Then drive for a while (ideally 10 trips so the ECU adaption will be complete) and then read the codes, if any, again.

This will give you proper diags to work on which, when you post them, we can help with.

I would not run or even crank the car in the meantime as the knack'd loom may result in unburned fuel getting into the cat which will burn hot when ignited and may nail the cat....the ECU usually turns off the injectors to the pair of cyls suferring misfire - all assuming it can still control them with your loom!

 

[Thegemmesabogie]

So you think it's only confined to the wiring near the cyl head heat?

This from the air mass meter plug

The inside of the ecu plug.

And the inside of the throttle actuator body.