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  #1  
Old 09-20-2003, 09:50 PM
Wadester
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Unhappy Surprise, I did something really stupid.....

Hi guys,
My Mercedes is an '84 500SEL. The occasional things that pop up with my car are bad enough but when I do something that actually CAUSES the problem....well...I'm embarrassed. I was working on identifying what is probably a fuel pump relay problem when I did the dastardly deed. I unplugged the fuel pump relay while the engine was turning over trying to start (yes, really long arms). So now the problem is not just an intermittant short in a relay, now I'm not getting any spark from the coil at all! Could I have actually shorted out the coil somehow when I removed the relay???? Is there some other kind of fuse or fusible link I don't know about?? Is there a way to test the coil? All fuses are still good. What was I thinking???

By the way, this forum has saved my bacon more times than I can remember.
Thanks in advance,
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  #2  
Old 09-20-2003, 10:08 PM
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Join Date: Mar 2000
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Pure coincidence.

The ignition controllers are a weak link in those MBs but its more likely the ign controller was the reason why the fuel pump relay wasn't working, if that is the case.
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Steve Brotherton
Continental Imports
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Bosch Master, ASE Master, L1
33 years MB technician
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  #3  
Old 09-20-2003, 10:21 PM
Wadester
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Thanks Steve. and the ignition controller is where????
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  #4  
Old 09-20-2003, 10:29 PM
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At the end of the green wire from the distributor.
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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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  #5  
Old 09-21-2003, 08:08 PM
Wadester
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Could you please lie to me a tell me that something cheaper is broken? ha ha ha not really that funny.
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  #6  
Old 09-21-2003, 09:15 PM
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You know.... it is what it is.

The distributor contains an armature and winding arrangement that rotates causing an induced voltage wave. This wave is read by the controller who uses its syncronicty to time the openning and closing of the coil primary circuit.

So if you are lacking spark, you are missing the openning and closing of the coil primary. If the signal is at the controller there isn't much else.
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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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  #7  
Old 09-22-2003, 02:15 PM
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A quick way to identify what system is the culprit for a "Crank no start" condition on KA-Jetronic systems is to listen for the frequency valve. If you hear the frequency valve buzzing while cranking, or when you first turn the key to position 2, the fuel pump relay is working. This quickly indicates, or points to a "no spark" condition.

The ignition module failure blues.

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  #8  
Old 09-27-2003, 09:26 PM
Wadester
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Okay, I'm assuming the green wire coming off the distributor that "feeds" a signal to the ignition control module SHOULD have some voltage coming through it while the engine is turning over - right? Because there isn't any voltage that I can detect with my multimeter. So now the inevitable question - what now?

Thanks a million for your feedback up to this point guys!
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  #9  
Old 09-28-2003, 01:17 PM
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The only way you will see voltgage from the dist is using a very LOW A/C scale. Unplug the green wire from the Ignition control unit. Conect one meter lead to the center connector in the wire, and the other lead to the outer metal shell of the connector. Crank the engine and you will problably see less than 1 volt A/C. If you see anything on the meter, the pickup coil in the dist is problably good. If it turns out that the Ignition moduel is bad, get an MSD 6AL Ign moduel from a speed shop. That is what I did and saved myself much money. It works great, has a tach output that is compatable with your 500SEL, mileage increased , Power increased (not much, but some), works with the MB coil,etc.
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  #10  
Old 09-28-2003, 11:35 PM
Wadester
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Wow, Thanks a million for the heads up on the MSD ignition, I'll definitely check it out!
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