W124 E200 with no ignition on cylinders 1 and 4

[joe prosser]

Need info on PMS ignition control unit MB#0185451032 bosch#0261200608. Car (W124 E200 with M111.940 engine) has dropped ignition on cylinders 1 and 4 and the coil is OK...swapped it over with the coil for 2 and 3 but fault remains with 1 and 4. Any advice, repair options or pictures of stripped down unit would be gratefully received

 

[bolide]

I'd suspect a bad wiring loom or bad ECU - or both

Nick Froome

 

[joe prosser]

Hi Nick,
My S124 is a late model (registered in Jan 1996) and the wiring loom insulation still looks OK. I have experienced the spaghetti like insulation on some of the early W202 C-class cars and mine is no where as bad, maybe due to youth. The supply to the coils is via two cables, solid black and black with white, which terminate as a two pronged plug mounted on the inlet manifold between runners 1 and 2. A short length of cable connects from a socket on this plug to the coils under the inlet manifold between runners 2 and 3 (for coil 1and 4) and runner 3 and 4 (for coil 2 and 3). All this cabling is flexible and not at all crumbly. Exposure to the air flow has kept things OK. All this points at a bad Ignition control module. I was wondering if any members had opened one of these up and taken any pictures. Replacements seem very pricey and I have experience of repairing electrical devices.

 

[bolide]

It doesn't have an ignition module like the older cars - it's all in the ECU. Google W124 ECU or search this forum for advice on testing & etc

Normally the ECU output transistors fail due to shorts in the loom feeding the coil packs

On most W124s the ECU is not keyed to the car so a replacement will work. AFAIK only late cars with DAS are more problematic. I don't know how to identify a car with DAS

You might be able to pick up a replacement ECU fairly cheaply secondhand - I would think an E200 ECU will be cheaper than one for a 280 or 320

Nick Froome

 

[joe prosser]

Hi nick, you're right it is the ECU but so many use this in error when referring to other modules that I find I get better results using PMS IGNITION MODULE, especially when searching internationally. One guy in the Ukraine found that he had caused his PMS module to die when oil/fuel/condensate had trickled down the vacuum line to the MAP sensor on the module itself and this had caused corrosion of the circuit board. He replaced his module but has now put an inline filter on the vacuum line brtween manifold and module to absorb any moisture.
Good engineering design is not just making things work but catering for potential failure modes like the above Ukrainian chap. A predictable ignition coil failure mode is to short out electrically. I would assume that this eventuality was designed for in the ECU to prevent a failure cascade. A short due to insulation breakdown (very poor choice of wiring by Mercedes) should look to the ECU like a bad coil.
Just been quoted £475 for 17 year old second hand ECU!!! Anybody pulled one of these modules apart to see what jewels and gold lie within? pictures would be good.

 

[Stratman]

I'm 99% certain there was a thread on here some time ago where the poster replaced the output transistors in the ECU.

It may be worth your while spending a few minutes getting to grips with the foibles of the forum 'Search' facility.


Stop Press:- This is the one


And welcome to the forum

 

[neilrr]

I'm 99% certain there was a thread on here some time ago where the poster replaced the output transistors in the ECU.

It may be worth your while spending a few minutes getting to grips with the foibles of the forum 'Search' facility.

Stop Press:- This is the one

That thread is about a faulty HFM unit. joe prosser needs a PMS ignition control module which lives on the OS inner wing & looks like this -

018 545 10 32 is an extremely rare unit, I have never seen one & it doesn't show up in MB's EPC.

I have the correct PMS unit with the follow on part number, the successor to 018 545 10 32 if you like.

joe p I can't PM you so if you are interested in finding out more put up an email address & I'll get in touch.

 

[bolide]

That thread is about a faulty HFM unit

Do the E280/320s have this unit? I've never seen one

Nick Froome

 

[grober]

4 cylinder engines only I believe. Didn't know they were found on the w124---- common on the early W202 1.8/ 2 litre C class 11 engines- but only the ones with adjustable inlet camshaft . [ WORTH A BREAKER SEARCH?] I think BBA Reman may do a remanufactured exchange unit for £475 also but with a warranty??? http://www.bba-reman.com/catalogue/DetailedProduct.aspx?DetailedProduct=475

 

[neilrr]

Do the E280/320s have this unit? I've never seen one

No, on W124s it's E200s only. E280/320s are HFM.

PMS units cannot be repaired, at least not properly in my experience.

A correction to my earlier post, it's on the NS inner wing.

 

[grober]

FOUND THIS LIST OF POTENTIAL REPAIRERS SUPPLIERS ON A SWEDISH SITE might be worth a look on their web sites?

e.g http://en.hitzpaetz.de/

 

[bolide]

No, on W124s it's E200s only. E280/320s are HFM

I assumed all the post-facelift cars used AFM. Assumption is, of course, the mother of all f-ups so apologies for sending this thread off in the wrong direction

Is this unit a version of the EZL or some kind of halfway house between that and the HFM system? Dos it have an ECU as well?

The only generalisation I've found you can make about W124s is that you can't generalise about them

Nick Froome

 

[joe prosser]

Hi Neilrr,
My email address is [email protected]. I agree that these devices are not fixable. I confess that in my frustration I put a Dremel mini disc to the cover of mine (it defied my attempts to remove it), just to have a look inside. Most of it consists of a metal slab with a plastic slab glued to it. In the middle is a rectangular block with dimensions corresponding to the top and width of the Mercedes Benz lettering and the bottom of the Bosch part number as shown in your excellent photo. About 10mm below the cover is a 10mm diameter hole within which is a filter. My guess is this is to allow 'atmospheric' pressure against which the vacuum from the inlet plenum tubing is referenced. I had expected a rubber sheathed mat of accessible electrical components, if they exist they lie within the bonded cMAP core and or within the banded plastic metal sandwich base. The device, looking now like a Borg cast off, still works in as much cylinders 2 and 3 run quite happily; amazing that not only is idle maintained but that the car can be pulled, slowly, with just two cylinders firing! My intention is to now swap my module with that of my wife's car, also a E200 W124 estate but with auto transmission her module is 018 545 7032. I can only borrow this module for a short while as I may just lose my conjugal rights. If my car is put to rights as believe it should be then I'll need a replacement for mine for a permanent fix.
Just as an aside some mentioned the connection between the W202 and the W124. THe M111 engine in my car is machined to accept a cam sensor but does not have one. It takes its timing from the crank sensor that detects two opposed points on the flywheel so it knows at least which is top dead center for cylinder 1+4 and cylinders 2+3. Spark occurs every time piston is at top dead center (wasted spark ignition) but what I have never been able to work out is how the ECU knows when to time the fuel injection or if it too injects on every rotation. When sourcing spare coils to try and sort out my car the most abundant source was a pile of W202 C class cars at the breakers yard; no W124s at all!. It was interesting to see examples of the evolution of the W202. The early versions have the same inlet manifold and throttle with ignition via PMS ECU like mine but also with the cam sensor. Slightly later models switched to MAF with HFM ignition. Later models have an alloy inlet manifold on which the throttle body is mounted lower and horizontally. The coils on these are within the spark plug gallery on top of the engine and ignition. The low tension leads to the coils on these often look well baked with brittle insulation. On the last models the inlet manifold is hard plastic, although on this last point I may be mistaken as this may have been a W210; hard to tell with no screen bonnet, front wings and most everything stripped off.

 

[neilrr]

Joe,

If you are swapping over a known good PMS unit into your car CHANGE THE COILS before doing so or you risk frying the good PMS unit.

 

[grober]

posted in error

 

[joe prosser]

HI Stratman,
Thanks very much for the input. I had a look at the thread you suggested and I see that it was initiated by Grober who has also addressing my problem. The ECU featured is not like mine and is the same as the one photographed by Neilrr. There seem to be such a range of ECUs it makes one wonder why a generic unit with circuit selecting 'jumpers' was never devised by Mercedes.

 

[grober]

If you look at the appended PMS diagram you will see that the injectors are also paired. They are supplied VIA the ignition 12v SUPPLY and earthed in pairs 1+4 [ ECU pin B4] and 2+3 [ECU pin B13] VIA THE ECU. While this 50% injection may seem wastefull its better than the old CIS [ continuous injection system] which supplied fuel continuously! For that reason only the crank position sensor is required for injection timing.

 

[joe prosser]

Hi Neilrr,
What is the best way to find out if any of the coils I have are defective? I now have four: the original one serving cylinders 2+3 (doing a sterling job keeping the engine running on two cylinders!); a salvaged one one serving cylinders 1+4 (but still not firing); a further salvaged one that was first tried in the 1+4 position before being swapped out; and finally the original coil for cylinders 1+4 that was replaced to try to fix the lack of ignition.
There must be some other way of testing coils other than inferring their status because they destroy the ECU. Bosch/Siemens engineers must be aware that they had to protect the ECU in response to any potential coil failure mode. Should I have the coils checked out by a professional?

 

[grober]

IGNITION COILS SHOULD READ PRIMARY 500-800 OHMS
SECONDARY 5OO-1,000 OHMS seem a bit high to me but just quoting a reference.
Exact values may vary but comparison of the replacement coils you have with the known good one should give you a reference

these guys claim?? to be able to sort them. Mercedes ECU fault - Misfiring

 

[joe prosser]

Hi Greame,
Brilliant explanation!! Well that settles a question that has been nagging me for ages. Hard to believe that 50% of the injections are on the back of closed valves, but it seems to work fine if a little inefficiently.