THIRD (yes, 3rd) 300-24 EZL failure in 1 YEAR
 

Hello All,

This is a request for any ideas on what might be the cause of the THIRD (yes, 3rd) EZL failure in 12 months.

My son and I will start some electrical diagnosis this morning but I would much appreciate any input from the clever chaps out there.

Relevant information includes:

• Different coil, cap, rotor arm and leads in all cases – first leads old Beru, then new NGK then new Beru. Plugs always non-resistor and correct.
• So I must assume that it is not a fault part downstream of the EZL.
• CPS still measures around 800 ohms as it always has.
• I have maintained the HT system in this car from 1997 to 2019 without incident.
• I know all the basic rules, obviously including thermal paste, clean contacts, etc., etc.
• OVP relay different during 2 out of 3 failures.
• Alternator regulator changed after the second failure.
• Before each of these 3 failures, the car was performing like new.
• Perfect starts – as always – I have never suffered from the damp HT problems, even in wettest winter.
• Until July 2019, the HT (and EZL) in this car has been 100% reliable due to fastidious maintenance by me.
• I have had this car for 22 years so I know it pretty well.

What do I plan to do now? Basically, diagnostics:

• Read fault codes in search of relevant codes – NONE last time I tested, 2 weeks ago.
• Check continuity of all earth (ground) connections at and near the EZL.
• Check EZL to coil leads.
• Then what???
• THIS IS WHERE I NEED YOUR EXPERT INPUTS PLEASE.

Awaiting any and all suggestions as this is getting TOO EXPENSIVE and I now have only one EZL left!!!

My thanks in advance.

RayH

Sounds like you have covered almost everything but I didn't see mention of the battery. It should be a full size battery. I'd also only use a battery rated at least 800A EN, and upon testing be capable of 650A EN. The starter will crank the engine over with less than 300A but the voltage will drop rather low doing so. When voltage drops, current increases to do the same work. While the EZL will certainly be designed with safeguards, repeatedly dipping into the edge of allowable limits may be enough to eventually take out an EZL.

I am not familiar with that model. I don't think they sold it in the US. I am not familiar with the EZL specifically either. However I am familiar with transistorized ignition control units in general. I am guessing a few sensors connect to that like cam sensors and crank sensors? Maybe knock sensors? I see a couple big connectors on it. Is it possible you have a marginal crank sensor for example? Just guessing here. Otherwise, I am guessing you are using older salvaged EZL's and it could just be that they were all near their end of life. Transistors and other parts can degrade with use in different ways, and heat and high voltage can exacerbate this process. If you get it working you could see if there is a specialist shop that is good with scope diagnostics and they could look at some of the signals into it and see if anything looks suspicious.

Thanks for inputs. The EZLs are inherently old so that may be an issue - however, even the "new" one I've just installed was made in 2003.

Battery is a new full size MB, much larger than the original MB battery.

Sunday 14th June update:

Checked all around diagnostic socket wiring, measured relevant earths etc. All appears good.

My only worry is the cheap-feeling brand new Beru plug wires. Similar to those that were installed (brand new NGKs) during EZL failures 2 and 3. Again, I had no trouble with older Beru wires installed 10+ years ago - WHY DID I CHANGE THEM AND BRING ON THIS MISERY???

So, the only thing I can do is get hold of a genuine MB set of wires and hope for the best.

And possibly get a new alternator to assure the smoothest current delivery.

Yes, I could find a true expert who could run diagnostics - oscilloscope etc - on the system to look for any voltage spikes that may be the cause of these repeated failures.

New 1200€ EZL now installed and car started from cold with its usual perfection. It’s like new!!!

I’m not going to use the car for a while as I reflect and plan.

Huh.

R

No EZL failures in 22 years and then 3 fail within 1 year?

That sounds very much like something outside the EZL and not the ezl itself.

Could be an intermittent short or something.

Finding the real cause of your problem is going to be a challenge I feel.

M104 with ke-jetronic was sold here only in the 300CE coupe/cab from 90 to 92 and 300SL same years I think.

cha-ching :beer:

They do say its a must after replacing the EZL to change out the coil for a new one .

With my battery in my trunk,I with all vehicles,run a extra ground to engine block from battery. Mercedes is bad for depending on unitized body for ground.I learned this running nitrous,ground is very important.

The coil is not integral to the EZL?

Thanks all. I'm thinking on the lines of alternator replacement. After all, it's lasted 30 years so I can't complain.


R

Update 19 June 2020

Continued to check electrical connections around battery. Noted the following:

The "front" controller - ABS I think - behind the battery was loose. Nuts that secure had not been tightened. Was this my fault? Possible. Would it cause any problems in earthing the unit? Is this a clue? I really don't think so but now we're in "desperation" territory so anything is considered.

The positive lead from the battery leads to a junction with numerous connection. They looked a bit corroded so were removed, Dremeled clean, copper greased and reinstalled.

Nothing else of an electrical nature looked suspicious so did general clean-up and reinstalled battery etc.

A new alternator and starter motor (both 30 years old) are on order and the local garage is on alert for installation when they arrive.

I'm trying to source a spare EZL of the following types:

A0125452032 (Bosch 0227400738

A0125452132 (Siemens EZ0051 5WK6 K30575HR1

A0105459532 (Bosch: 0027 400 736).

A0105459632 (Siemens: 5WK 301, I think)

PLEASE DOES ANYONE HAVE ONE OF THESE?

As always, thanks in advance for any comments, suggestions, EZLs!

Best to all.

RayH

Did you install the ELZ with thermal paste? I'm not sure what the MB part number is for the past but it looks like the same stuff used to install heat sinks on computer chips.

Also what is the type of spark plug that you use? It has to be a non-resistor plug as outlined here:

http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/104/15-1031.pdf

These plugs are hard to get nowadays

Yes, always non-resistor. These were NGK.

I replaced the NGKs with genuine MB.

R

Yes, it's basically the same as used for CPUs. In my case it is a tube of RadioSpares heatsink paste.

R

Interesting.

I only know of one thing that will kill these quickly like that. Cranking the engine without spark plug wires or coil wire connected. So I suspect secondary but you tried all that with the exception of the coil. As others have mentioned it may be worth while to replace that. But you really want to avoid doing a shot gun replacement of parts with $500, last I checked if its even still available, part in place. So I would recommend doing the basic checks of resistance on the coil.

If you are assured that the car will run for at least an hour without destroying the ELZ, then bring it somewhere where the system can be checked on a scope. Good luck finding a person who has and can use an automotive scope these days. You may have to purchase a standard scope and buy automotive leads to read the secondary voltage. It might require a learning curve but you can try it out on another car.

Thanks for your input.

The first EZL failed with a new Beru coil.

The second with an older genuine MB on I had in stock.

The third failed with another, different, new Beru coil.

This afternoon I installed a new, genuine MB coil.

I cleaned and copper greased all the connections and checked earth/ground resistances - all close to 0.2 ohms as measured from the battery negative. This is a great improvement on initial measurements after the third failure.

Next week, the local garage will install a "new", remanufactured Bosch (genuine?) starter motor and alternator. He will be instructed to check, clean and reinstall all cables, including the engine earth strap.

Beyond that, I'm lost!!!!

Yes, it's an expensive business. The car is operational now with my new 1200€ EZL. I've ordered another used EZL for 220€ and I shall use that one until confidence returns. The new one will be with me at all times, together with the tools to replace.

And I may get yet another used one for safety.

This may make me sound very rich - not true. I spent some cash getting my old 300CE-24 restored as my "last car" - I'm 68. So, I cannot go back; I MUST resolve this.

Life's fun isn't it?

Ray

this

Yes, always install heatsink paste.

R

Overvoltage can damage electronics. Rig up a high quality voltmeter so you can read it from the driver's seat while driving. Voltage should not exceed 14.5, even momentarily.

Duke

Thanks for that. I've ordered an automotive oscilloscope that might come into play next week.

R

13 July 2020

Hello again All,

Well, I new, secondhand EZL has been installed. I am reluctant to install the "new" 1200 € one from MB until I am certain that the issues are solved. Time will tell.

Since the 3rd EZL failure, the following has been done.

1. New plugs, MB.
2. New leads, Beru.
3. New coil, MB.
4. Complete cleanup of all areas including distributor cap and rotor - only 9 months old.
5. Complete cleanup and reinstall of all earth straps, including the main engine strap underneath.
6. New (Bosch reconditioned) starter motor.
7. New (Bosch reconditioned) alternator.

Of course, I have no idea yet if all this has solved the problem. I shall not have confidence until a year (?) has passed. Even then 100% confidence is unlikely.

Just as before, the car now starts, drives and stops like a new car. Since its overhaul at PCS in 2017 it has never been better. Apart from this costly EZL issue.

Do I notice any differences after this latest set of "improvements"?

Yes, it now starts, even when hot, like a new car. Before, when hot, it would sometimes fire and then not keep running unless I kept the starter motor turning a little longer. That was hardly a problem as it was just a matter of remembering to hold the key in the start position for an extra half second.

However, it now seems to spring immediately into life and settle into an even idle under all circumstances. I shall be doing a more typical run today and shall be able to confirm this with greater confidence.

More as it happens.

And, as always, comments welcomed.

All the best.

RayH

Non-resistor plugs are no longer in production I've heard.

Take a Multi meter and measure the resistance between the top terminal and the center electrode.

If it has ressistance then your best bet is to find new old stock Bosch F8DC plugs on ebay.

My 300SE needed plugs and I found NOS plugs on ebay for cheap.

The plugs I installed are genuine MB, made in France. I think they are Beru.

NGK supplies a suitable non-resistor, I've got the reference somewhere for those interested. Oddly, these EZL failures all happened on the NGK plugs. I can't believe there's a correlation.

And then there's Champion C11YCC,, as stated by MB.

I've used MB, Beru, Bosch F8DC4 and NGK and never noticed any difference.

My last diagnosis will be measurements of the cable between the EZL and the coil. I've already verified this briefly but I'll do it now more aggressively by measuring the resistance whilst moving the cable to see if there's any intermittence.

And so it goes on.

R

R

yes the model of the plug can tell you/us if it's a resistor one or not.

https://www.ngk.com/learning-center/article/174/ngk-numbering-systems

Ray, I always run Bosch F8DC4 plugs in our 124 vehicles per the advice of an experienced MB-trained tech at our local MB dealer 20 years ago. It's critical to keep an eye on the condition of the distributor cap & rotor. Check for evidence of moisture inside the cap. Replace as-required. As mentioned the thermal paste under the EZL is important too.

Thanks and, yes, all that noted.

And to christuna, NGK today only lists 5K ohm resistor plugs. That's a change.

Ah, but I did find the reference for the NGKs I had installed until recently: BP5EFS. Apparently available here:
https://www.jdm-sparkplugs.com/shop/standard/bp5efs/

R

The best way to make sure you have non-resistor plugs is to just remove one of them and measure.

These are what are now installed: A0031596803.

R

I'd follow what Christuna has noted.

Our local dealership supplies MB plugs alleged suitable but they are no longer resistor types

Next. Beru Leads a'int what they used to be.

Check the connections at the fuel pump for corrosion. In fact check every electrical connection you can find. Even go to the trouble of changing all your fuses. Any aluminum ones change them out.

Good luck with that car. It's a shame a rare EZL can render it down.

Ive heard the 24's were ezl killers but I haven't had that proof myself. My Siemens one failed abruptly last year and I was able to track down a bosch unit from a sl for $300. Replaced it and its been good. Interestingly enough, my alternator was intermittently dying for a week before my EZL failed, I suspect low voltage precipitated the failure.



The idea that lower voltage is causing higher current across the ignition transistor doesn't hold water to me, current decreases as voltage goes down. Less "pressure" to push the electrons across the coil, less overall power being dissipated. I'm thinking it might have been electrical noise from my failing alternator beating on the electronics in the unit but I don't know. My replacement unit has not failed yet after a year of DD.





I have one more EZL that works and still have my old siemens one for dissection/repair. I was thinking of giving the EZL a more stable life if another one fails. Move the harnesses and mount the EZL under the dash with a fan on the back of it. This will keep it from experiencing high temperature deltas literally every time you drive, especially in winter. It will also isolate the EZL away from the strut tower (i read one guy with an sl500 had his die after a pothole). I would also add a 500uF cap across power and ground at the unit to absorb noise. To top it off I thought of running the EZL's output to an aftermarket MSD ignition to take the work load off the EZL. At that point it may not even generate heat if its only being used to generate a signal. Im also wondering if my failed unit still works, ie still getting a signal to the transistor but the transistor is blown. When I have a place and garage soon I plan to open up my siemens one and poke around with a scope. Hope this posts gives you some ideas..At min replace your coil, they rarely go open circuit but their always weak and if it bleeds to primary your gonna kill an ezl. Also scope the voltage supply.

Thanks Turbo.

Yes, you are thinking on very similar lines to me. The low voltage theory doesn't hold water to me.

Alternator spikes are one theory of mine, hence the alternator change.

My impression also is that the destruction takes place at start-up. I cannot be 100% sure but I feel I heard the engine fire before the EZL died and then nothing.

And I really do not support the idea of EZLs needing any further cooling than good heatsink paste to the bulkhead. I have never felt my EZL get any hotter than "tepid", even on a hot day. Certainly nothing like a hot as a hard working power amplifier driving some naughty B&W speakers.

And also on heat, these cars were supplied to Saudi where things get seriously hot. Did all the EZLs fail?

Like you, I am now hoping for the best. I do not know if my measures will bring about success or failure as the car still starts - and it did before, for a few months!!

Oh well.

RayH

When mine died I did not have any stuttering at all. Just cranked. As far as thermal stuff goes, I agree, it doesn't get that hot. What I'm concerned about is the cycling change in temperature leading to a breakdown of something in the ezl-be a solder joint, bond wire or solid state junction. Mine was dead when I went to start the car, i assume it died when the ezl cooled off, something in its circuitry just went open. But then that kills my dying alternator theory (and my alternator WAS dying, its been replaced right before the ezl died) because you'd expect it to die suddenly while running. I did try experiments to get it to work again but wasn't successful. I tried freezing it and starting the car as well as getting it hot but never even had a stumble. I need to open up that one I have and see if I can find if any parts of the board are still working to get some insight into why they die.



I'm also wondering...Are Siemens ones more likely to fail? both my working one and spare are bosches.

More food for thought.

My impression is that mine have died on startup - did I detect a bit of firing before death? Can't be sure.

I have NEVER had any running issues before death. This car has always been a prompt starter and a smooth runner. Even at 400+ K Kms, it performs like a new car until sudden death.

This problem arose after I replaced plugs, wires and coil. And the genuine MB cap, rotor and shield were all only a year or two old. Did I screw up something? I've maintained the ignition system in this thing for 20+ years so it's unlikely but possible. But what? Are these things really so fragile? Difficult to believe.

The ones that have failed for me are: 2 x Bosch A0105459532 and 1 x Siemens A0125452132.

The one that's working fine right now (or was yesterday in 35C heat!!!) is a Siemens A0105459632. So, I cannot say that Siemens or Bosch are more or less reliable.

More as it happens.

RayH

IS THIS A CLUE?

To recap; 3 EZLs blown in the past year despite almost new HT components, including coil.

I had the impression that death was at startup as I was vaguely conscious of a brief "fire" before death. We concluded that, possibly, some electrical surge was blowing these EZLs.

So, the latest measures included checking and cleaning all accessible earth/ground connections. And then a new (rebuilt by Bosch in Spain) starter motor and alternator have been installed.

Of course, I know not if I've solved it until the car does not fail to start for some time; a year, two years?

But, I have noticed one change.

Before, when closing the electric windows (front ones on a coupé - significant current), the revs would drop slightly and then recover.

After our measures and the new starter and alternator, when shutting the windows, absolute stability. No revs drop. Nothing.

I can't get too optimistic yet as the car was always performing like new - better by far than when I took delivery when it was 6 years old with 130k Kms (80k miles) on the clock.

What do we all think about that?

As always, best to all and keep those comments coming in.

RayH

If it were me I'd take one of the old units apart and look for the specific issue that killed it. It's also odd to me it wants non-resistor plugs since those make noise and electronics generally don't like that. Some think one or the other affects the ign due to current draw but that's ignorant. I'd put resistor plugs in but up to you. I'd also be wary of the coil because new does not mean good. I think I'd rather have an old coil that has proven it works than a new one.
If the coil shorts internally it can cause excessive current draw, which may only appear when hot btw. If your transistor(s) in your module have blown I'd just install some external ones.
Back when I was a kid I got tired of points altering my dwell and timing as they burned (and the cost of new points) so I put a pair transistors between the points and coil, problem solved. Transistors make heat so if moved out of the box then your other components will be cooler.
Or just lose the box and put in an aftermarket setup or home made setup. I see your box has a vac line, so if this is how it controls vac advance, and you still want vac adv, then it just got more complicated. Not impossible, just more complicated. I mention these options if that module is expensive and/or hard to find.

25 August 2020

Not exactly an update but a status report.

After 3 EZL burns we've:

> Checked and cleaned all earth connections.
> Installed a new alternator (90 amp).
> Installed a new starter motor.

Has anything changed? No, the car is running like new but it was before the first EZL failures.

To recap, I said that my impression was that the EZL death was on start up. That was just an impression; there is no evidence of this.

EZL death may be happening on shut down. Does this give us any other clue? Not that I can see.

>>> One small difference is that, if the car is idling and one raises the electric windows, the rev counter doesn't move. Before installing the new parts, the revs would drop noticeably and recover.

Any clue here?

To my mind it must just be the grater capacity of the new alternator.

As always, any and all comments welcomed.

Best to all.

RayH

A thought came to me today: Relays can pump a high voltage spike into the cars system when they're turned off. A relay is just a mechanical switch but it uses a coil to create a magnetic field to actuate said switch. When you turn it off it's similar to how the ing coil works; it generates a high voltage spike. Note I said similar, not just like. This is not good for delicate electronics and while I've never had an issue, it can be one. This may explain why your ign box dies on shutdown because you just killed power to some relay(s) that pumped a voltage spike into the system.
So, if you have relays that weren't in there when the car was new, like maybe to control an elec fan or who knows what, it/they may be the cause. It may be that when the ign is on the system as a whole (battery included) can absorb the spike so no harm. If say you hooked said relay to the ignition power circuit so it only works when that's on, now when you turn the key off you just excluded the battery and everything else leaving the ign box alone in a circuit making a voltage spike. A spike looking for a place to go in an isolated system is like a drunk in a bar looking for a fight and everyone clears the room except a 98lb weakling (ign box), which gets punched right in the face. Corny analogy but it was entertaining for me.
Not saying this is it, but certainly a possibility and seems very reasonable to me. So if you have said relays you may want to put diodes across the coil pins of the relays(s). I suggest a Schottky diode because they're faster and will work better than a silicone diode at catching spikes. Just be sure it's rated for a couple hundred volts which I think most are? Then solder it backwards across the coil pins. If soldered fwd you'll just smoke it and/or blow a fuse. The point is the coils voltage spike is reverse polarity so when it fires off the diode is right there acting as a short.
Since we're on the subject, it's possible an oem relay is causing it too. Maybe the spike is getting to the ign when normally it doesn't. I suppose if an ign switch has more than one contact inside it could break the relay circuit a microsecond before the ign? Or maybe whatever oem relay(s) are on a circuit that has a single diode they share but either the diode died or the circuit was moved to that shared by the ign box, or the ign box circuit moved to the relay circuit. Like maybe one or the other circuit stopped working so someone moved it to another spot. Just guessing, but a thought.

Another thought is to simply make or buy a filter for the power to the ign box so it's safe no matter what kind of weird crap is going on elsewhere. Ironically, the filter uses a coil. Basically fight fire with fire. Other weird crap could be something like the coil in the starter is kicking back which would cause it to die the moment you let off the starter which you described. As in maybe the circuit for the starter is connected to the ign, or is somehow bleeding into it. A long shot theory here but if say the spikes only place to go is in the ign switch, which is normally cut off when you release the key. With wear it makes copper and carbon dust, and the key likely has grease for said contacts. Copper and carbon in grease make it conductive enough that a spike just may blaze right through it so the spike that had nowhere to go, now does. Long shot but who knows. So do you try to find whatever gremlin that may be anywhere, or just put a filter on the thing? Or at the very least put a diode on the leads to the ign.

And as mentioned earlier, I'd use external transistors to actuate the ign coil. Option A; have the internal transistor(s) power the external one(s). If you check a now bad ign box and the output transistor(s) are not working the then you could use the pos (or neg) that drives them to instead drive the new external one(s) and save the box. I'd use two transistors because it's easier on the transistor since a coil is a heavy load, at least the coils I've used. Plus if one fails for whatever random reason you're still good to go. I'd assume the factory used two for the same reason?

What you mentioned about the power windows and rpm is a battery thing, so my guess is the new alt is simply charging the batt properly. When the batt is weak it relies more on the alt which is why you see a drop in rpm. If the batt is good it powers the windows with much less voltage drop, it's the voltage drop that triggers the alt to kick in, and how by how much, so the less power the batt had, either old and weak or just low, the more the alt generates and the more it generates the more of a load on the engine.

I'm not a fan of modifying standard parts. The car's original and I intend to keep it that way.

So, my quest is to find out the cause of these failures. With the new alternator and starter motor all is well but I shall not know until the current EZL doesn't fail. Ridiculous, really, as it's difficult to make a judgement on something that hasn't happened!

Other restoration work continues and all is, for the moment, well.

Watch this space.

Thanks for your continued interest.

RayH

m104 motor EZL----6 cyl (300) 24 valve

Old JC has done little as saviour of my EZLs.

Is the solution for me to go to church more often?

R

hey, going to church is always a good plan! God fixes my cars all the time but my w124 6 cyls have not been able to get an appointment for some reason......reminds me of the old joke where the guy is asking God "why me?" and this voice comes down from the heavens "well....there's just something about you the pisses me off!"

God is very busy now trying to keep safe and healthy all of the COVID patients and the people and animals suffering from the fires in the west coast. God always helps but sometimes in ways we don’t understand.

Amen amen