Starting problems - Mercedes-Benz Forum
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post #1 of 13 (permalink) Old 05-16-2019, 07:21 AM Thread Starter
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Starting problems

Hey guys,

Need some diagnostic expert advice. A while back had trouble starting my 380SL. Cranked but wouldn't start. Changed the ICM and it started right up. Drove it for a day and then it died and wouldn't start again. Put another ICM on and changed the green ignition wire, old one had bad ground wire to the distributor. Drove it yesterday for several hours and then was going to put it up in my garage and drove about two blocks and it died and wouldn't start again. Got it to my garage and put another ICM on and it started right up. What could be making the ICMs fail in the way they are? What wiring etc should I be checking and how?

Thanks,

Mike
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post #2 of 13 (permalink) Old 05-16-2019, 03:22 PM
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The first thing I would do is put one of the "failed" ignition modules back in and see if the car starts. If it doesn't, put a timing light on a plug wire, crank the starter, and see if you're getting spark.

I personally think you have a flakey fuel pump relay. If you get in a no-start situation, have someone crank the starter while you put your hand on the fuel pump to see if it's running.

Good luck,

CT

Chuck Taylor
Falls Church VA
1998 SL500
1959 220S
1970 280SL
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post #3 of 13 (permalink) Old 05-17-2019, 09:14 AM Thread Starter
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Hi. Thanks for the reply. I put the old ICM back on no start. Getting spark. What could be "blowing" the ICM? I will check the fuel pump today.

Mike
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post #4 of 13 (permalink) Old 05-17-2019, 11:24 AM
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Originally Posted by mikeford60 View Post
Hi. Thanks for the reply. I put the old ICM back on no start. Getting spark. What could be "blowing" the ICM? I will check the fuel pump today.

Mike
If you're getting spark then it sounds like your ICM is working. Of course getting spark at the right time is just as important as getting spark.

Which icm's are you using? Original or the new solid state versions?

I once mocked up my ignition system on the bench and posted a video of it working by my spinning the distributor by hand. It's how I discovered that my ignition was working but my green wire was intermittent.

Spark, compression, fuel... all in their proper time. That's all you need for the engine to run. If you have spark, and we can assume compression... then what you're missing is fuel.

I'll look for the video.

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post #5 of 13 (permalink) Old 05-17-2019, 12:29 PM
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We have a couple of those fuel pump relays if you need one.
https://www.autohausaz.com/catalog/c...lay?s=d&page=1

And an Ignition Pickup Connector Wire:
https://www.autohausaz.com/catalog/c...rts?s=d&page=3

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post #6 of 13 (permalink) Old 05-17-2019, 12:58 PM Thread Starter
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Thanks Do you have the ignition control connector-the grey wire with black connector to the icm Part number 1075404008?
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post #7 of 13 (permalink) Old 05-17-2019, 01:02 PM Thread Starter
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Hi. Thanks for the reply. Using a programma rebuilt bosch unit. Second one. I put on the newest ICM and it started. I put the previous one on and it wouldnt start. Put the first one back on and it wouldnt start until i jiggled and moved the wires. Im thinking there is a short somewhere in the wiring from coil back that is making the ICM cut out? Not sure though.
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post #8 of 13 (permalink) Old 05-17-2019, 01:30 PM
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post #9 of 13 (permalink) Old 05-17-2019, 01:36 PM Thread Starter
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no but i have one on order.
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post #10 of 13 (permalink) Old 05-17-2019, 04:04 PM
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Originally Posted by AutohausAZ View Post
We have a couple of those fuel pump relays if you need one.

And an Ignition Pickup Connector Wire:
The ignition pickup wire you are selling is a URO part. The URO ignition pickup wire (a.k.a. green wire) has a known problem with the distributor side connector. URO is aware of the problem and promised to notify us when it was fixed but I've never heard from them on the subject again.

I would avoid using the URO green wire if at all possible. If you must use it... you need to tighten down on the grip of the connector on the distributor end of the green wire. Apparently the molded connectors on the end of the green wire are too big which causes them to make intermittent contact inside the distributor. I fixed mine by inserting a jewelers screwdriver between the plastic mold and the metal of the connector and then twisting the screwdriver causing the connector to squeeze closed a little more. That appears to have been an acceptable workaround to the fact that URO used the wrong size connector.

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