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.