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silver 1992 w140 500 se
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Discussion Starter #1
I have a 1992 500 se and I have a low voltage (~2.5v) at tickover on the LV side of the ignition coils, increasing rpm increases voltage. I have checked the wires from the ezl to the ignition coils and they have good insulation and contact and the ezl is getting good voltage.

The only code the ezl has shown is 17 and 18 (only 18 once)

17 Crankshaft position sensor faulty
18 Magnets for crankshaft position sensor (CKP) not recognized.

I have checked the resistance of the crankshaft position sensor and it is within limits.

Could the crankshaft position sensor cause a low coil voltage and how do I get it out as searching the forum it seems a lot easier on other w140s?

I can follow the wire but I cannot see the sensor to get a socket on it.
 

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Being a 92 maybe your wiring harness Is bad.

Beyond that, check vacuum lines, check for the resistance of the cam solenoid. Someone mentioned recently that low vacuum to the map sensor can cause improper manifold pressure and throw these codes.

Sent from my SGH-T989 using AutoGuide.Com Free App
 

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silver 1992 w140 500 se
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35 Posts
Discussion Starter #3 (Edited)
upper wiring harness good, lower unknown. I've got a maf not map but will double check vacuum lines. Only just noticed I can check crank and cam sensors with a mutlimeter on ac volts so will do that also. If sensors work I am suspecting ezl.

Will keep updated.
 

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1998 S600 LWB 2011 GLK 350 4matic 2013 Sprinter 2500
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I changed my left side sensor a few weeks back. You'll need a ratchet extension with a wobble or a universal swivel.
 

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silver 1992 w140 500 se
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35 Posts
Discussion Starter #5
Looks to be the ezl as all the sensors and wiring check out, my cranckshaft sensor was was 5 VAC at tick over so well above limits though haven't got an oscilloscope on it to check waveform.

Need to buy a new ignition control module, they are pricey.
 

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600SEL
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How did you measure primary coil voltage? You really need an oscilloscope to make a proper diagnostic. Here is a scope picture from my car (600SEL) for your reference.
 

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silver 1992 w140 500 se
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35 Posts
Discussion Starter #7
Measured ignition coil voltage with a multimeter across it, made a test extension for the sensors and measured voltage with multimeter. I would imagine that as long as the ignition control module gets enough signal to spark it should output full voltage at all rpms.
 

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silver 1992 w140 500 se
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Discussion Starter #9 (Edited)
I thought that was back emf and the actual voltage provided by the ezl. I didn't think the ezl had anything to boast the car's normal voltage. I've got these numbers from the service manual

Voltages at idle
Battery voltage V 13.0 - 14.5
Ignition coil Circuit 15 V 13.0 - 14.5
Ignition coil Circuit 1 V 12.5 - 14
Primary ignition voltage V 200 - 350
Secondary ignition voltage kV 8 - 20

Now I'm confused. What I do know is I have a weak spark at idle (pulling off the spark plug lead).

PS, thanks for your help guys

As the power to the ezl is good and the wires from the ezl to the ignition coils are good must it not be the ezl which is at fault (coil resistances are in order)? Which are circuits 15, 1 and primary and is the only way to measure them with a multimeter?
 

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600SEL
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Multimeter is not going to help you. You need to use a scope to see primary voltage, and if it looks like on the picture I've attached, everything is good.
What other symptoms other than weak spark do you have?
 

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silver 1992 w140 500 se
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Discussion Starter #11
Fair enough. Just discover another symptom my ezl is 014 545 45 32 which is meant for the 500. It also had plastic on the bottom between the unit and the car, I presume it should be removed prior to fitting to aid heat transfer.

When I start the car it is powerful but it gets worse and worse. Restarting it can bring back the power, it is also running rich which you can tell by the smell. I think the spark has been getting progressively work as previously I lost the spark previously and changed the rotors and distributors and that got the spark back but i think the ezl has been getting worse all the time. I checked the coil resistance and continuity and they were within limits
 

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silver 1992 w140 500 se
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Discussion Starter #12
Still waiting on part from US. However just took off both distributor caps as I saw a crack at a corner and they were both arced over. They are less than a year old and I must have covered about 5000 miles. They are plastic and Beru not Bosch.

I have the old Bosch one and an old Beru that I replaced last year and the old porcelain of the Bosch is fine but the Beru is arced over. I replaced a working Bosch and now obviously faulty Beru, should have stuck to Bosch. I hope I have the receipt to take it back, Beru is not so good.
 
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