W124 - ECU or Coil?

[kth286]

RayH

Just to keep you informed, the later models after your's, changed the way that fuel and ignition was provided.

IT was ALL controlled from one computer( ECU) so all solid state, with no rotating parts
ie no distributor.

It is the Mercedes method of car evolution.

This engine setup was really the test bed for the next generation of midsize car the 210 E class.

So the last (3.2 litre) 124 cars and the early 210 generation cars had the same engine and control systems.

 

[tricky100]

RayH

Just to keep you informed, the later models after your's, changed the way that fuel and ignition was provided.

IT was ALL controlled from one computer( ECU) so all solid state, with no rotating parts
ie no distributor.

It is the Mercedes method of car evolution.

This engine setup was really the test bed for the next generation of midsize car the 210 E class.

So the last (3.2 litre) 124 cars and the early 210 generation cars had the same engine and control systems.

Mines a 96 w124 320 so presumably would have the newer system you described , does this mean that it shouldn't suffer with this wiring loom problem?
I was going to maybe replace this part of loom as a precaution but not to sure what needs replacing . Thanks .

 

[maxicab]

Electronic Mercs

Hi, a 96 will be the electronic, distributorless, later type mentioned above. It WILL have this wiring loom achilles heel. Check carefully through the history. It may have been already replaced; otherwise check it (maybe get a knowledgeable friend too). You'll need an Allen key, a 10mm spanner and a screwdriver and a strong nerve for what you might find and undo the 6 Allen bolts and 2 10 mm nuts right on top of the engine, disconnect the air intake pipe, lift the cover off and have a good look at all the LT wiring leads in the top ignition compartment - especially from the wiring loom to the 3 coils. If the insulation looks dry, cracked and falling off, put it all back carefully and try and find a loom repair kit from MB. I never knew such a repair kit existed (and neither did my 2 prof. experts) and bought the whole loom for £550 plus VAT and fitting. If the loom looks dodgy, don't disturb it by changing spark plugs or any HT leads until it's done. A previous post somewhere on this site (try searching this site for "W124 wiring harness woes" or "howeshouse" posts) around 11/07 showed a nice diagram of the ignition leads and coils etc. Lots of other previous posts have relevant info too. Good luck. david

 

[tricky100]

Hi, a 96 will be the electronic, distributorless, later type mentioned above. It WILL have this wiring loom achilles heel. Check carefully through the history. It may have been already replaced; otherwise check it (maybe get a knowledgeable friend too). You'll need an Allen key, a 10mm spanner and a screwdriver and a strong nerve for what you might find and undo the 6 Allen bolts and 2 10 mm nuts right on top of the engine, disconnect the air intake pipe, lift the cover off and have a good look at all the LT wiring leads in the top ignition compartment - especially from the wiring loom to the 3 coils. If the insulation looks dry, cracked and falling off, put it all back carefully and try and find a loom repair kit from MB. I never knew such a repair kit existed (and neither did my 2 prof. experts) and bought the whole loom for £550 plus VAT and fitting. If the loom looks dodgy, don't disturb it by changing spark plugs or any HT leads until it's done. A previous post somewhere on this site (try searching this site for "W124 wiring harness woes" or "howeshouse" posts) around 11/07 showed a nice diagram of the ignition leads and coils etc. Lots of other previous posts have relevant info too. Good luck. david

Thanks , ill have a look . I knew they had a problem with the engine wiring loom but i thought it was just that the wires broke down with age . Seems a bit confusing having read this about heat damage and other posts about engine loomsand ECU's contaminated with engine oil ? Are these linked or totally differant ?
Presumably if its just on the low tension side i can quite easily make up a new wiring loom myself ? i suppose the real damage , when people have needed new ECU'S and coils is caused when wires fused together and shorted out ?

 

[Bolide]

In theory, yes you can make up a new loom. In practice you'll find that the degraded insulation continues right up to the plugs attached to the loom and all the plugs are encapsulated. This means you'll have to make joins to old cable at every plug

Bearing in mind the amount of work to replicate a loom, and that it may not do the job, I suspect you'd be better off with a new one from MB

Nick Froome
www.w124.co.uk

 

[rayhennig]

Electrics, Electronics: Cleanliness and more cleanliness ...

You're right, I hadn't appreciated that this was a later car without conventional distributor.

I do think that my policy of cleaning every contact that I can get at pays dividends. Every time I access a hitherto undiscovered (by me) are of the car, I unplug, apply contact cleaner and ensure cleanliness of all contacts. Multi-way connectors, fuses, you name it and I clean it!

I'm convinced that this approach pays dividends - anyway, the only cost is a little extra time and some cleaning fluid.

RayH

 

[kth286]

tricky100

Your car is NOT affected by oil into ECU. The loom problem applies however, and can happen the next time you start up the car without any warning. It may blow a coil OR can blow a coil and ECU - big money !!!!!!!!!!!!!!

If you intend keeping the car have a new engine wiring loom - I can fit it for you for a bit of beer money.

Even if you sell the car it WILL be a good selling point to show the bill for a new loom and it will last for another 12/15 years and hopefully much longer if Merc have now improved the design.

PS. Be aware different loom and part numbers depending on car spec and options.

You need to give your VIN to Merc parts dept or post on this site, then I, or another that subscribes to the Merc EPC can determine correct part for you.

 

[tricky100]

Thanks for clearing that up , ill have a look at it tomorrow and see what its like (assuming it makes it till then ). It runs faultlessly but in the large folder of bills there is no mention of this work so i dont know what to expect now .

 

[tricky100]

Well just removed the cover and had a look and to be honest all looks fine . Everything is obviously original and not been replaced , ie all 3 coils have the same small surface rust but no bodged pvc tape repairs so best to let sleeping dogs lie . Didn't remove any of the black sheafing on the LT wires but no signs of overheating and the wires inside the sheafing could easily be manipulated so not fused together (hopefully). No i told you so's please when i post about missfire's in a few months, thankyou.:grin:

 

[maxicab]

Post 20: "Eventually the penny dropped after checking everything electrical connection wise I could find was tight. The little grub screw for want of a better word that holds each of the coils in place in one corner of each coil, is also the electrical connector for the coil to the earth of the engine. And the rear screw was a little bit loose! Apart from a jolt from the HT plug, I was delighted. It all made sense and the grounding obviously wasn't reliably occurring through the other 2 screws which don't necessarily touch on the metal of the coil body. Amazing this isn't a more common problem, as these screws are pretty fragile and in fact I've ordered 3 new screws from MB as the screwdriver slots in mine were all damaged. Here's hoping I've solved it."
Well it's still running perfectly ever since. I replaced all 3 grub screws at a cost of 55p +VAT each. Oh joy!

 

[maxicab]

And well done Tricky! No sense in interfering if it's all fine. It is quite surprising though as these engines run hot and all that heat building up in that little airless compartment should be enough to fry the insulation after 12 years! Maybe it was changed at some time, or maybe your car has had an easy life. Good sign either way. Maybe fastidious cleaning helps as I guess if there's oil around it will be more likely that the insulation will burn. But don't use a high pressure washer on these engines as the electrics are a bit fragile. Do remember those grub screws though when you change the spark plugs under the coils next time. Bite the bullet and fork out £2 for new screws. It may save you a fortune and months of heartache.

 

[maxicab]

It's Back!

Well the old problem is back despite running well for some time. It was really pretty bad today - running poorly most of the time with very poor power. I've spent a fair bit of time on this site and others looking for information. There is a lot of stuff out there and it doesn't all make sense to me. I've ordered 3 new coils in case one is intermittent, but I don't have great faith that this will cure the problem
A question or two though. Is there a "limp mode" on this model? The symptoms seem similar to several other posts describing intermittent loss of power in later cars; they were frequently described as having gone into limp mode. It does seem as if my car just flips in and out of this low power, rough running (misfiring) state. How many of the following exist as possibilities on my car:
Faulty MAF - unplugging and plugging in the sensor connector seems to make a difference, but doesn't stop it misfiring when it's unplugged. Seemed to be able to make the misfire come and go when messing around with the connector sometimes but not reliably so.
Inlet manifold connector
EGR valve problem
Throttle activator
Catalytic convertor
Crank Sensor
O2 sensor (is there one?)
OVP (what is this?)
Voltage regulator
Low Battery voltage
Relay (which one and where?).
Any advice or education welcome
Thanks

david

 

[bigasotonuk]

Hi,
Did you replace the plug caps under the coils? these can break down an cause intermittent misfiring problems, they did on my C Class.

 

[MarkwithaMerc]

E240-same problem as this E124?

Hi
I have been careful not to start a new thread but I am unsure if this one applies to me. I am new to Mercs, having fallen for them in place of Jaguars so please be gentle!
Subject: 2001 E240 estate
Problem: Pretty much the same as Maxicab under.
I have had the car since last December. Bought it with a slight idle misfire but thought a service etc would sort it.
Had the service done by a friend who knows Mercs but only has Sykes hand-held for resetting fault codes etc. He reset 6 faults at the service: mainly sporadic and random misfires, cascading through Lambda and cat converter faults. He reset these and all was dandy until i pulled out from a car park, engine cold, and uphill.The engine management light came on and all power was lost. (Limp-home mode?)
I pulled into a layby to let the traffic pass, switched off, started again and although the eng management light was still on, power was resumed, still with idle misfire but with slightly reduced gas mileage.
This was a couple of weeks ago. 12 new plugs, swopping over coil-packs and general checking of everything has had no improvement BUT, I reset the faults again, only to have them appear yet again. Then three days ago I jumped in, started the car and all light have disappeared and engine power/mileage is back to normal! There is still the idle misfire though.

Question: can this be the same as Maxicab and his 124? I have had the cover off the loom for injectors and coil LT supplies but cant find anything wrong and no 'wiggle' makes a blind bit of difference!
I LOVE the car to drive over a Jag but I really would like to get the car reliable so wifey and self can go on holiday safely! How do I continue??

Thanks guys!

 

[Juddian]

Welcome Mark

I don't have the foggiest idea about you problem, but i think you would be far better to start a new thread, as i think yours will get lost cos of yours being a 210, and anyone with thoughts on your problem may miss your post completely.

No probs about a new thread, they really are a nice bunch of fruit cakes round here generally.

Why not copy and paste your post with a small explanation.

 

[maxicab]

Hi. Yes have changed the 3 plug caps under the coils (twice in fact!). They were referred to somewhere along the line in this thread (thread 3 and 15 it looks like). As usual with this problem, everything I do seems to work for a while, then the problem restarts. Hence me wondering if there's a limp home mode that I didn't know about. Somewhere in this forum someone said it's no good just disconnecting the MAF, you may not see much difference at tickover. You really need to drive it. I haven't done this; maybe I should.
Mark I know little about your model, but from what I've read here it does sound like you are switching into limp home mode. Some of the wizzes here may be more able to help if you say the W model no, engine type, fuel type and mileage and service history. Your symptoms sound rather like those described for a faulty MAF. Look up this forum under MAF. Look hard! It seems you can unplug the MAF sensor and the problem may be largely cured, then you buy a new BOSCH MAF (not chinese or ebay copy). It seems also that fault code readers can miss a MAF problem. The MAF is on the air intake just near the air filter and has a twist fit lead going to it which is easily unplugged. Good luck and home I'm not talking rubbish. david

 

[MarkwithaMerc]

Hey guys, thanks for the swift response! I gave up on the Jaguar forum when i had problems cos i thought they were all dead! Murky men definitely aren't!
I will do as Juddian says and re-post. Meanwhile, i have taken note of Maxicab's story as i think it can't be too far removed from mine. See you in E country!

Thanks again

 

[maxicab]

Thanks Mark, good luck.
My query about what an OVP is is partly solved!
I came upon this statement on the well recommended Isle of Wight ECU expert's website:
"ALL MERCEDES MODELS - Intermittent poor/non start or poor idle/running. Has vehicle got overvoltage protection relay (also called OVP relay or surge protection relay)? If yes REPLACE! any problems here can cause fuel injection system mis-operation."
Does this ring true with any one? Anyone know where this OVP can be found? Any advice on replacing it?
Thanks, David

 

[maxicab]

Hi again. The misery continues. I thought I'd cured it. Ran perfectly for another week, then the misfire problem resurfaced on Friday (I still don't know if this could be a deliberate limp-home mode protection mode sent out by the ECU in this model??).
I fitted the 3 new coils and they made no difference, but fortuitously noticed some burned looking insulation tape around some heatshrink covered wires entering into the engine-facing side of the fuse box. I investigated further and discovered the bunch of 5 wires could be wiggled and the misfire would come and go. I don't know what any of these wires do. Cut and spliced the wires and thought I had it beat, as it then performed perfectly until Friday. So I don't know if this repair did any good or not. But while in the fusebox, I noted that a previous wiring repair had been done to the blower motor fuse (the lack of a fuse in the usual space, despite a functioning blower had always puzzled me) - it had been replaced with a separate more modern 25A fuse on the end of a long piece of twin wire. And it looked like the current drain must be very high as the plastic fuse, although not blown, was literally melted and welded onto its holder. And looking carefully at the original fuse holder space, it was clear that it had in the past been over-heated. Could the blower be drawing huge amounts of current, even on low blower speeds, although seemingly working normally? AND could this current drain be upsetting the other electrics and causing my intermittent electrically based misfiring problem by upsetting the ECU in the same way as a faulty OVP can? Should I turn off the blower next time the misfire occurs and see what happens?
Thanks for all the help, David

 

[maxicab]

Oh I should also have said that I found and checked the OVP relay - Its beside the ECU -it looks as if it was replaced in 2002 - it's the single fuse, 9 pin type, made in Hungary. It also fits in with indecipherable (French) electrical repairs carried out according to service record receipts. It fits into a 9 hole socket, but only 7 of the sockets seem active, in that 2 are just plastic inside. I also pulled out and looked at the 2 other relays on the other side of the ECU. One was smaller and green, I don't know what it is, the other I'm pretty sure was the fuel/kickdown relay. Both looked clean and OK to an untrained eye. BUT I also noticed that one of the screws holding the OVP to a metal bar which also is screwed right through to the firewall was missing. The other screw only holds the OVP to the metal bar. So the metal bar was kind of swinging in the air. The metal bar also holds the ECU in place. DOES it also electrically ground (earth) the ECU? I wonder could this cause my problems? I haven't replaced that screw as I couldn't find a suitable one, but I tightened up quite a bit the other screw anchoring the ECU to the floor of its shelf. Runs perfectly since, but I'm claiming no victory yet!