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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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Yes, excessive system voltage will cause the power dissipation in the EZL switching transistor to increase. I would perform the voltage check both at both idle and with the engine rev'ed (say, about 3,000 RPM). The alternator's output capability increases with shaft speed, so a duff VR may be more of an issue at speed. The one thing this test may not catch is an intermittent VR.

I would also make sure the battery is in good nick. Excessive internal battery resistance will allow the system voltage to vary more than it should.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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Trying to catch up here, but I was still waiting on feedback from the OP re. voltage readings as posted in #5
 

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300 CE 24V Sportline
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Discussion Starter #23 (Edited)
I'm thinking on the lines of voltage spikes, regulator etc. New regulator installed after 2nd failure. 3rd EZL dead.

Voltage readings have already been verified as OK but I'm unable - no 'scope - to read transients. Shall talk to a local garage chap on Friday.

To recap, these 3 EZL failures occurred after I'd decided that new plugs and leads were a good idea. Why did I do this?

I did it because we all agree that 1st class ignition components are vital with these cars.

My recurrent thought ...

Each failure is on start up. NEVER when driving. It never stops. It just doesn't start. I never know now if, for example, after 2000 kms of perfect performance, it's going to start. After spending a fortune getting this car just right, this is grim!

More than that, I have the impression that, each time, it fires on start up and then stalls. Then nothing. Dead EZL. New one installed this morning, perfect start. BUT FOR HOW LONG???

I'm tempted to change the alternator.

I'll put in a new OVP for peace of mind.

Once done, only time will tell.

What I want is a 'scope display of transients that could be killing these EZLs. Only when these are eliminated will confidence be restored.

Is this making sense?

R
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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I'm thinking on the lines of voltage spikes, regulator etc. New regulator installed after 2nd failure. 3rd EZL dead.

Voltage readings have already been verified as OK but I'm unable - no 'scope - to read transients. Shall talk to a local garage chap on Friday.

To recap, these 3 EZL failures occurred after I'd decided that new plugs and leads were a good idea. Why did I do this?

I did it because we all agree that 1st class ignition components are vital with these cars.

My recurrent thought ...

Each failure is on start up. NEVER when driving. It never stops. It just doesn't start. I never know now if, for example, after 2000 kms of perfect performance, it's going to start. After spending a fortune getting this car just right, this is grim!

More than that, I have the impression that, each time, it fires on start up and then stalls. Then nothing. Dead EZL. New one installed this morning, perfect start. BUT FOR HOW LONG???

I'm tempted to change the alternator.

I'll put in a new OVP for peace of mind.

Once done, only time will tell.

What I want is a 'scope display of transients that could be killing these EZLs. Only when these are eliminated will confidence be restored.

Is this making sense?

R
This fact (only dies upon power-up) tells us that "most likely" something in the power supply section of the EZL is being damaged/fried during start-up. This is when the power supplies are charging up caps etc and the current surges are the highest.

Why is yours more vulnerable than other million EZL's out there? I would certainly look further into your 12V system for spikes, peak voltages, etc.
The culprit most likely is in your alternator/regulator/etc.

Before you throw away a fried EZL perhaps you can open it up and have a look at it to see if there are burnt out components. And what part is burnt out. AFAIK the EZL could be potted and make this a messy project.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Yeah, pulling out potting is a PIA. I'm more in the camp that his particular alt is spiking on start up. Without scoping it, I don't know how you could tell....and it probably doesn't happen on each start up.

Put in a new alt of 100 amp or better.......I always thought the factory one to be a bit anemic for accessories. These big Group 48/49 batteries need to be slaved to a better alt.

Kevin
 

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300 CE 24V Sportline
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Discussion Starter #26
Thanks all. I'm thinking on the lines of alternator replacement. After all, it's lasted 30 years so I can't complain.

R
 

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Discussion Starter #27
Have you run a voltage test across your battery at idle with no load and then with all your accessories on? And if so, what were the voltages? Flooby could weigh in, but I'm thinking an overcharging alt could play hell with an EZL.

Kevin
Alternator regulator (Hella) was replaced not long before the last EZL failure.

Yes, the alternator is my current favourite.

When you say "overcharging", do you mean that it's pumping out more than around 14 volts? My thinking is that, if the internal diode bridge is faulty, it could be sending spikes, despite the new regulator - possible?.

R
 

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Discussion Starter #28
Any ideas for 100 amp alternator that's a plug and play fit top my 300CE-24?

I shall buy best quality so I imagine that will be Bosch, Hella. Any other 1st class makes?

And yes, my feeling is that something's throwing a vicious spike at start up and I feel that I've heard a single "fire" of the engine just before the EZL dies. I can't swear to that.

R
 

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Couple of questions: What is the time to failure on the EZLs? In other words, how long has each one been in place before it failed. If possible, how many miles?

Maybe the thought of protecting EZLs was not deemed necessary 30 years ago but it sure is an issue here. Can anyone with electronics experience come up with a protection circuit suggestion? If its possible it would be a whole lot better than swapping out components hoping to come up with the magic combination.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Any ideas for 100 amp alternator that's a plug and play fit top my 300CE-24?

I shall buy best quality so I imagine that will be Bosch, Hella. Any other 1st class makes?

And yes, my feeling is that something's throwing a vicious spike at start up and I feel that I've heard a single "fire" of the engine just before the EZL dies. I can't swear to that.

R
I really think your alt is spiking on start up but probably not all the time. Yes, more than 14 volts. I looked into new alts sometime back and found this one. It's been yrs though so you might want to revisit fitment....but I think it was a direct bolt in. If you can even find a new Bosch(most all are re-manufactured), it's going to be crazy expensive. Clark passed this one as OK:Amazon.com: Valeo 439095 Alternator: Automotive

Shopping around, I found it as low as $188. Living in France, not sure what's available to you.

Kevin
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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Forget this scope business. Just break out the trusty multimeter and measure voltage at the battery terminals with the car at idle and at startup. Any value above 14.5V is danger zone, and anything above 16V is impending Chernobyl syndrome on your electrical system.

I worked on a Alabama trashcan a.k.a. ML class a while back that had a alternator go rogue. As a result, the battery exploded and destroyed the tray and and a whole bunch of other stuff with it.

FWIW, the alternator on the Alabama trashcan was putting out 18Volt.
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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Forget this scope business. Just break out the trusty multimeter and measure voltage at the battery terminals with the car at idle and at startup. Any value above 14.5V is danger zone, and anything above 16V is impending Chernobyl syndrome on your electrical system.

I worked on a Alabama trashcan a.k.a. ML class a while back that had a alternator go rogue. As a result, the battery exploded and destroyed the tray and and a whole bunch of other stuff with it.

FWIW, the alternator on the Alabama trashcan was putting out 18Volt.
I agree, although for complete characterization of the VR function, one needs to also measure the the system voltage at a higher engine speed (I have suggested 3K RPM but anything over 1,500 should do). While 99% of the time, failure of these VRs is due to worn brushes, a leaky/shorted field switching transistor or a bad internal Zenor diode can cause the system voltage to rise or fluctuate with engine speed. It's easy enough to take the additional measurement.
 

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Discussion Starter #33
I really think your alt is spiking on start up but probably not all the time. Yes, more than 14 volts. I looked into new alts sometime back and found this one. It's been yrs though so you might want to revisit fitment....but I think it was a direct bolt in. If you can even find a new Bosch(most all are re-manufactured), it's going to be crazy expensive. Clark passed this one as OK:Amazon.com: Valeo 439095 Alternator: Automotive

Shopping around, I found it as low as $188. Living in France, not sure what's available to you.

Kevin
I've just ordered Bosch alternator from here:

Apparently new and genuine Bosch and not reconditioned. If all that's true, it's a great deal. Or have I been conned by a wretched Brit - like me?

Now we await with interest.

I shall ask my local garage man to check as many earth and other connections during installation.

R
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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Couple of questions: What is the time to failure on the EZLs? In other words, how long has each one been in place before it failed. If possible, how many miles?

Maybe the thought of protecting EZLs was not deemed necessary 30 years ago but it sure is an issue here. Can anyone with electronics experience come up with a protection circuit suggestion? If its possible it would be a whole lot better than swapping out components hoping to come up with the magic combination.
Interestingly, on these earlier cars, the old style 50 watt Zener diode type OVPs actually provide some "backwards" protection to the entire electrical system against system voltage spikes of short duration. This is because, when a properly functioning OVP is "on" (e.g., the car is running), that 50 watt Zener is effectively placed in parallel with the battery/alternator so it will clamp any system voltage spike to the 22.5 volt value of the Zener. Loads on the back side of the OVP (like the EZL) will not, however, be protected against longer spikes/increases in system voltage because once the OVP fuse blows (as will happen with a long term spike/over-voltage condition), the Zener is effectively disconnected from the rest of the system and the backwards protection will be lost.

I'm sure the engineers at MB were fully aware of this and felt that this level of protection was sufficient for the EZL. So, in short, if your OVP is new and the fuse isn't blowing, voltage spikes are not your issue.
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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I'm surprised that your OVP is not protecting the EZL. You said you replaced the OVP already. Perhaps even the OVP has it's limitations too.
And then your battery is also a filter here. Hopefully that is not an issue (itself and it's connections).

Unless you are an electronics engineer/savvy these intermittent over-voltages or spikes would be difficult to diagnose.

This is why I suggested perhaps opening up the damaged EZL to see if there are obvious signs. I would do that but as I said, it would be messy.
Unfortunately we do not have a circuit diagram of the EZL either.
 

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Discussion Starter #36 (Edited)
I'm surprised that your OVP is not protecting the EZL. You said you replaced the OVP already. Perhaps even the OVP has it's limitations too.
And then your battery is also a filter here. Hopefully that is not an issue (itself and it's connections).

Unless you are an electronics engineer/savvy these intermittent over-voltages or spikes would be difficult to diagnose.

This is why I suggested perhaps opening up the damaged EZL to see if there are obvious signs. I would do that but as I said, it would be messy.
Unfortunately we do not have a circuit diagram of the EZL either.
I am surprised too. I shall look at the OVP again and ensure that the latest, genuine MB one is in place.

As for opening up the EZL, no, not me, it looks like misery and, apparently, it's potted in epoxy and practically impenetrable. My son may give it a try but I cannot, as we Brits say, "... I can't be arsed"

R
 

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Maybe there is an under voltage problem?
Battery faulty since you say you have repaired the alternator already, and not blown the ovp fuse.
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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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. That contact connects to battery in the run and start positions and perhaps an intermittent connection (sometimes referred to as "contact bounce") is causing current (not voltage) surges at the EZL which are causing it to fail at start up. The OVP provides no protection against current surges, only voltage surges.

Have you tried the jiggly key test to see if maybe the contact is not solid? Just a thought . . . .
 

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Discussion Starter #39
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. That contact connects to battery in the run and start positions and perhaps an intermittent connection (sometimes referred to as "contact bounce") is causing current (not voltage) surges at the EZL which are causing it to fail at start up. The OVP provides no protection against current surges, only voltage surges.

Have you tried the jiggly key test to see if maybe the contact is not solid? Just a thought . . . .
Thanks for that and, yes, already considered and a brand new MB switch/lock assembly was installed before failure 3.

All the best.

R
 

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1990 300SL-24V, 1993 BMW 530i-V8 manual, 1999 SLK230 Sport
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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.
 
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