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1991 420SEL
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Discussion Starter #1 (Edited)
I have a 1991 W126 420SEL. From one crank to the next it wouldn't start.

I've been working on some other things recently but I'm not sure if they might be related or not. So, they may be worth mentioning or might be useless information.

It has a new battery. New high amp ebaY alternator. New plugs and wires.

Recently changed the fuel filter and gave it a lot more power. Had a couple difficult starts but only after sitting a few days and then noticed a fuel leak at the filter. Tightened it up a little more and fixed the leak. The hard starts quit immediately and for at least three more starts. Then had two more hard starts. The last hard start, I cranked it, moved it in the driveway to work on power window / welcome lights. Finished and it was just dead, hasn't started again. There were no blown related fuses. Searched for any blown fuse first thing and I did replace the dome light fuse but not sure when that happened and it's not on the same circuit I was messing with or related to ignition, as far as I know. Is any of this related? I have no idea but it's worth mentioning.

My first thought was that it isn't getting gas so I jumpered the 7-8 pen to manually turn on the fuel pump. Fuel pump worked but did not hear it running when I turned on the key, I replaced the fuel pump control box behind the firewall. Mostly because it was a cheap and easy place to start. Didn't make it start and still didn't hear the pump start when I turn on the key so I'm assuming that's normal. Also put the jumper in to force the pump on and tried to start but would not start. I don't think I have a fuel problem.

Moving on, I checked for spark and have none, at all, anywhere. No spark from wire to plug. No spark from coil to distributor. Coil does have power going to it when key is on. Rotary inside distributor does spin. Noticed the plastic was cracked a little but "shouldn't" keep it from working.

Pulled the ignition coil and took it to AutoZone to get it tested. Guy put a simple meter on it and pulled up some specks on the computer, tested the primary and secondary and said both testes are within range so, I'm assuming it's good. Note: he didn't test it with a fancy computer testing device as I was expecting after watching some youtube videos.

Granted this is the first time I've had a no spark issue ever but I have tried to do my homework on how to troubleshoot it. Here's where I'm stuck; if the coil is getting power and tests good then that says it isn't getting a signal telling it to do its thing. If the rotary is spinning inside the distributor that says its getting the signal to do it's thing, right? Seems like it should work and yet it doesn't so my lack of experience is causing me to miss something somewhere.

I'm dead stuck so any suggestions would be helpful. Feel free to mention "obvious stuff" because I don't actually know what I'm doing.
 

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1991 560 SEC 1994 E500 2014 E350 Cab
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7,029 Posts
maybe I missed it, are you getting your pumps to turn on at all now? Your new battery could be dead. Or at least not enough to turn on the pumps. Check that red wire on the positive cable and be sure its in tact as it provides 12v to fuel pump. It can also break with age when changing assembly back there. Trace your steps on that alternator, be sure you didnt damage a small wire on the reinstall, it is also brittle and I have seen others break them 10-12 inches up. All fixable but what makes new battery dead is a non charging or bad ground system. Or dead cells and lights on with jumpered fuel pump..
 

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17 Subaru Outback :)
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Check that red wire on the positive cable and be sure its in tact as it provides 12v to fuel pump.
I have seen this 'red wire' mentioned a few times. Are you referring to a wire that hooks up to the 12v post on the battery?
 

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'82 Euro 500SEL, '85 Euro 500SEC AMG WB Cabriolet,'86 Euro 500SEC RUF
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9,487 Posts
Yes, but only on Gen II cars.
 

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1991 420SEL
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85 Posts
Discussion Starter #6
I don't currently have a battery or alternator problem, as far as I know, that's all new and has been issue free for months. I could go turn the key and crank the car right now for the next ten minutes without it slowing down if I wanted to, it just wouldn't start because there is no spark.

I also don't believe I have a fuel pump issue, I've heard the pump motor run and gas squirting when turned on manually. Relay box aside, I know the pump works.

This car was in storage for several years. Previous owner didn't do any maintenance to speak of. I got it and replaced several parts this winter and put it on the road this spring. It has used 1.5 tanks of gas sense I have owned the car. I haven't driven it much. Fuel filer was changed when the light came on, just before the last fill up last month, that was half a tank ago.

Problem is, no spark. The coil tests like it should work and yet it doesn't. I've replaced one part at random so far and don't wish to continue down that costly and futile path. I have no experience with a no spark issue and need more troubleshooting info to determine exactly what part needs replaced to get the correct part.
 

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1991 560 SEC 1994 E500 2014 E350 Cab
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7,029 Posts
Well if battery, starter coil and charging system are good, then EZL or ECM. I am by far not an expert, and have no experience with 420, just my 560. Concepts are the same but your EZL is your ignition brain, left fender. You are not getting what you need when you turn on car so those brains for the ignition are on the fender well, and under the right side carpet, near the door hinges area. But search for this on the forum, and get a know good spare. You have a good ally in TN by the name of Grumpy560, he may have some spares to sell or loan....or extensive wisdom to share. Good to have a local fanatic to turn to for this stuff too.
 

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1991 420SEL
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85 Posts
Discussion Starter #9
Ahh, EZL and ECM, parts I didn't know existed. I knew their had to be something else somewhere in the ignition system but had no idea what. I'll start doing some research on these parts right away...
 

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1991 560 SEC 1994 E500 2014 E350 Cab
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1991 420SEL
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Discussion Starter #11
Couldn't really find how to test either of these but research said that the EZL is a common failure item. All things being equal I had a 50/50 shot of it being the EZL and got a used one on ebaY for $40. Changed it out in about 5 minutes. Turned over a couple times and cranked right up. Thanks guys! Also my Check Engine light is now out. First time sense I got the car.

Note: This 91 420SEL had a Bosch 0227400693 EZL thats hard to find and everything I looked at said that the 0035459132 EZL was basicly the same thing and it was easy to find. Only differences I could see is that the vacuum line plugged in at a different location, not a problem and the back was coated with white heat sink compound, bonus. I couldn't find any new and I figure used is used so I bought the cheapest for $40 instead of around $1000 for the exact same part in the exact same used condition. I'll probably do what others have done and keep an eye out for a cheap spare to put in my, whats been referred to as a "get me home box".
 

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300sel W109, 280S 70 , 220s 62. 230 66. Lancia Flavia 63.Pininfarina
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EZL failures in all 126 models or specifically 420?
 

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Like many of the electronics controls in our old cars, they do tend to fail at some point. There are places that refurbish them.
 

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'82 Euro 500SEL, '85 Euro 500SEC AMG WB Cabriolet,'86 Euro 500SEC RUF
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I try to grab all the EZL's I find in the bone yards. never hurts to have spares, and some to help others with sometimes too.

I coined the term ""Get Me Home" box.
 

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1990 merc 560 sec, 1984 merc 500 sec ,1983 Mercedes 380 SEC ; 2007 Discovery III
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438 Posts
Hi Green T,

can you send me the info on who refurbishes the EZL.

I am sitting with three EZL of the 8 pin type which do not work.

would appreciate the assistance.

if anyone has a spare one for the 1990 560 sec, would like to buy it.

C
 

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1991 420SEL
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Discussion Starter #19 (Edited)
I was hoping this thread was just a memory... Well, quit again. ordered another, didn't start, ordered another didn't start, have another ordered because I was going for a spare. :confused: I don't know what else would cause it to die and not start back exactly the same way. More specifically, theres seems to be 1-3 hard starts, as if to warn me its about to go and then its just dead and wont start. Last time it was a hard start then died while idling and wouldn't restart. First time its done that, could be something else unrelated. Suggestions?
 
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