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Your diagnosis seems pretty thorough. Are the EZL modules factory or aftermarket. Besides voltage spikes and overheating excessive current draw could be causing module failure. I would be looking at your input voltage as low voltage due to excessive voltage drop in the +15 circuit will drive current up in the module. You could try a ballast resistor in series with the coil primary. obviously this is not a repair but a diagnostic aid. That would lower the switching current. If you had an oscilloscope looking at inputs to the module would help determine if spikes are the issue Or excessive noise from a failing alternator. If not place your DMM on A/C volts and look for any ripple. Should be less than .1 volt A/c
 

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Discussion Starter #42
Have you checked your wiring harness going to the EZL. Some Mercedes had the biodegradable wiring harness and once that starts chaffing internally you are in for a big surprise.
I shall be checking as much as possible in that area but my car is pre-bio build date - it doesn't have that degrading wiring.

All the best.

R
 

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Discussion Starter #43
Your diagnosis seems pretty thorough. Are the EZL modules factory or aftermarket. Besides voltage spikes and overheating excessive current draw could be causing module failure. I would be looking at your input voltage as low voltage due to excessive voltage drop in the +15 circuit will drive current up in the module. You could try a ballast resistor in series with the coil primary. obviously this is not a repair but a diagnostic aid. That would lower the switching current. If you had an oscilloscope looking at inputs to the module would help determine if spikes are the issue Or excessive noise from a failing alternator. If not place your DMM on A/C volts and look for any ripple. Should be less than .1 volt A/c
These modules are all factory originals as there are no aftermarket replacements. They were not repaired ones either. The 3 failures included my original 1991 factory-installed unit and 2 spares I bought as a safeguard. The final one, now installed, is "new" (dated 2003) from MB main dealer in Bochum, Germany.

Regarding further tests, I no longer have a 'scope to I cannot observe ripple. I could try the DMM on AC.

I am inclined not to use the car until the new alternator is installed - I want to avoid another 1200€ going to MB Bochum.

Once installed, I shall run the engine and measure AC and other DC voltages in the area of the EZL.

As said previously, we improved earth/ground connections from battery neg to chassis and I was able to confirm much more solid continuity between battery neg and earth points around the EZL, including the common earth point on Pin 1 of the new EZL that now measures 0.09 ohms to batery neg.

Again, as said, these failures occurred after installation of new spark plugs and new NGK leads. That was the only change aside from a cheap Chinese 12v USB charger but I cannot imagine how noise from that could destroy EZLs - maybe I'm wrong.

As always, thanks to all and KEEP THOSE IDEAS COMING!!!

R
 

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This suggestion comes under the category of long shot, hail Mary, but how is your ignition switch? You say the EZL only fails at start-up, so I'm thinking that maybe the switch contact that powers the Fuse 7 circuit is intermittent.
This is the big mystery with EZL failure. You rarely if ever hear of the car dying on the road and the EZL being bad. These adventures all start (no pun intended) with a car that was under cold start conditions. Maybe the EZL packs up on the previous shut down but the main point is they rarely fail while driving.
 

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Have you checked your wiring harness going to the EZL. Some Mercedes had the biodegradable wiring harness and once that starts chaffing internally you are in for a big surprise.
Not applicable to the OP's model.
 

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..That was the only change aside from a cheap Chinese 12v USB charger but I cannot imagine how noise from that could destroy EZLs - maybe I'm wrong.
...
It shouldn't but cheap and Chinese are 2 things that don't jive with MB's of this era.

Unplug it, or better yet get a quality charger that is Qualcomm certified & approved (see link). I use Aukey chargers for the cars and at home. They are on the list.

 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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This is the big mystery with EZL failure. You rarely if ever hear of the car dying on the road and the EZL being bad. These adventures all start (no pun intended) with a car that was under cold start conditions. Maybe the EZL packs up on the previous shut down but the main point is they rarely fail while driving.
Yes, that does seem to be the case, although a friend of mine had his EZL fail at 65 MPH on the highway. I think that in general, power up is the hardest part of normal operation on electronic devices so it makes sense that one might see the most failures then.
 

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These modules are all factory originals as there are no aftermarket replacements. They were not repaired ones either. The 3 failures included my original 1991 factory-installed unit and 2 spares I bought as a safeguard. The final one, now installed, is "new" (dated 2003) from MB main dealer in Bochum, Germany.

Regarding further tests, I no longer have a 'scope to I cannot observe ripple. I could try the DMM on AC.

I am inclined not to use the car until the new alternator is installed - I want to avoid another 1200€ going to MB Bochum.

Once installed, I shall run the engine and measure AC and other DC voltages in the area of the EZL.

As said previously, we improved earth/ground connections from battery neg to chassis and I was able to confirm much more solid continuity between battery neg and earth points around the EZL, including the common earth point on Pin 1 of the new EZL that now measures 0.09 ohms to batery neg.

Again, as said, these failures occurred after installation of new spark plugs and new NGK leads. That was the only change aside from a cheap Chinese 12v USB charger but I cannot imagine how noise from that could destroy EZLs - maybe I'm wrong.

As always, thanks to all and KEEP THOSE IDEAS COMING!!!

R
If the plugs were correct and the NGK leads ohm out like original equipment, they aren't the problem. But I would throw that charger as far as I could away from me rather than risking another EZL.
 

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Discussion Starter #49
But I would throw that charger as far as I could away from me rather than risking another EZL.
Yes, so would I. And I have; it's history.

Although I can't see how a 12v USB charger could take out 3 EZLs.

Do you say this for any reason?

R
 

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No I don't have any experience with that type of situation nor do I have enough understanding of electronics to support my fear. In fact, in a thread I started a few months ago, the overall opinion was that chargers don't cause damage. That doesn't change how I feel about them. If you want to charge a battery, disconnect it first.
 

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1990 Benz 300E 2.6 (mine) ; 1994 E320 Wagon (wife's) ; 1993 300CE Cabrio, needs some TLC
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It shouldn't but cheap and Chinese are 2 things that don't jive with MB's of this era.

Unplug it, or better yet get a quality charger that is Qualcomm certified & approved (see link). I use Aukey chargers for the cars and at home. They are on the list.

that advise is only valid if your phone or whatever uses QC ... my devices use USB-C PD, which is the official current USB spec, QC, especially QC 2.x, actually violates the USB spec.

for USB C devices, I've had very good luck with these chargers,

they fully charge my Pixel 3a phone and my Huawei MediaPad M5 tablet from nearly dead in record time. I also use their wallplug chargers with the same specs ('PowerIQ 3.0')
 

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No I don't have any experience with that type of situation nor do I have enough understanding of electronics to support my fear. In fact, in a thread I started a few months ago, the overall opinion was that chargers don't cause damage. That doesn't change how I feel about them. If you want to charge a battery, disconnect it first.
Could there be some confusion between USB chargers that take power from the car to power/charge external devices such as a phone versus battery chargers that put power back into the car electrical system? I'm confused.

I can't see how the former could cause an issue because the draw less current than the lighter they displaced, even the non-USB compliant ones whereas the latter could certainly do some damage if not properly designed/used.
 

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1990 Benz 300E 2.6 (mine) ; 1994 E320 Wagon (wife's) ; 1993 300CE Cabrio, needs some TLC
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ah, the cigar plug style of car battery charger wouldn't be of much use on a W124 as the cigar outlet is shut off when you turn off the engine.
 

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Discussion Starter #54
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
 

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Have you tried SL Parts in Holland (see link)? They're one of the largest classic era MB breakers and usually always have stuff like this in stock.



 

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Have you tried SL Parts in Holland (see link)? They're one of the largest classic era MB breakers and usually always have stuff like this in stock.



Thanks for that. Yes, I know these people and their prices for EZLs still reflect the 2000+€ price for a new one. MB in Germany now quotes 1100€ and in France 2300€!!

Thanks again.

R
 

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As you know Ray, EZLs for the M104.980 are not to be found for a pint and a sing song.

It really is the Achilles of all the cars that have this specific engine, sadly.

I really don't see the need to have a spare (let alone multiples) on hand until the moment you need it. A OVP on the other hand yes, as it will leave you stranded in the case of the HFM/Motronic driven M104 engines.
 

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Discussion Starter #58
As you know Ray, EZLs for the M104.980 are not to be found for a pint and a sing song.

It really is the Achilles of all the cars that have this specific engine, sadly.

I really don't see the need to have a spare (let alone multiples) on hand until the moment you need it. A OVP on the other hand yes, as it will leave you stranded in the case of the HFM/Motronic driven M104 engines.
Ha! The moment you need it is the time the effing thing refuses to start when you're 100s of kms from home.

I intend to carry a spare, plus the necessary tools, until such time that confidence returns.

You're right, this has turned out to be an Achilles heel with line, even after 21 years trouble free.

Life can be a bitch sometimes.

R
 

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I honestly think that the Jetronic cars (of all makes and generations) don't qualify for daily driver status anymore since several years when gasoline started being tainted with ethanol. At best, they're a 2nd car or better yet weekend toy.
 

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I honestly think that the Jetronic cars (of all makes and generations) don't qualify for daily driver status anymore since several years when gasoline started being tainted with ethanol. At best, they're a 2nd car or better yet weekend toy.
You and I need to disagree over the pints that your referred to earlier.

R
 
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