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Quote:
Originally Posted by mysocal911 View Post
That's a very rare occurrence when a no spark ONLY condition is the problem.
Then I must be one unlucky dude because I had one with a failed component that created a no spark situation and the car wouldn't start.
Old 03-20-2017, 04:04 AM
  Pelican Parts Technical Article Directory    Reply With Quote #81 (permalink)
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TIP: I use a simple LED test light to test the speed/ref sensors. While cranking the speed sensor flickers the light very quickly while the ref flickers it much slower but still visible. No fancy meter or scope really needed to do a fast quick test.

The other test to do is try another DME from a known good car, it can easily help you quickly figure out if it's the DME or something else. For what it's worth I'm seeing a lot of ignition circuit failure issues in these DMEs, they are over 30 years old and have seen a lot of vibration. It's very possible this is a ignition circuit failure.
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1984 911 Carrera Cab M491 (Factory Wide Body)
1975 911S Targa (SOLD)
1964 356SC (SOLD)
1987 Ford Mustang LX 5.0 Convertible

Last edited by scarceller; 03-20-2017 at 03:27 PM..
Old 03-20-2017, 03:22 PM
  Pelican Parts Technical Article Directory    Reply With Quote #82 (permalink)
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Ingo,

I'll also add that re-soldering 30 year old solder is not a great idea. I always remove all the old solder then re-solder with new solder. Then scrub the area clean of all solder flux and finally re-coat the board with conformal coating for added protection. The repair really should be done carefully with the correct techniques, products and tools.

Quote:
Originally Posted by ischmitz View Post
Re-solder is only one of the reasons the spark output can fail in these DME. If you are handy with a soldering iron maybe you can try to fix it. However, the real test is to measure the signal inside the DME and understand why there is no spark output. If there is a bad component re-solder won't do a thing.

Ingo
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Sal
1984 911 Carrera Cab M491 (Factory Wide Body)
1975 911S Targa (SOLD)
1964 356SC (SOLD)
1987 Ford Mustang LX 5.0 Convertible
Old 03-20-2017, 03:27 PM
  Pelican Parts Technical Article Directory    Reply With Quote #83 (permalink)
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Hi Sal,
The OP brought his ECU to my house today. My car starts easily and runs fine. We swapped in his ECU and my car would crank, but not start. Later, when I put my own ECU back in my car, it started it immediately.
Just for curiosity, we opened his ECU to look for obvious defects and saw none. I told him that I have worked with you and suggested he consider sending his unit to you or Ingo or one of the other experts for evaluation.
I hope it works out for him soon.
Good luck,
Dave
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1984 Carrera 3.2
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Old 03-20-2017, 04:12 PM
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Quote:
Originally Posted by DaveMcKenz View Post
Hi Sal,
The OP brought his ECU to my house today. My car starts easily and runs fine. We swapped in his ECU and my car would crank, but not start. Later, when I put my own ECU back in my car, it started it immediately.
Just for curiosity, we opened his ECU to look for obvious defects and saw none. I told him that I have worked with you and suggested he consider sending his unit to you or Ingo or one of the other experts for evaluation.
I hope it works out for him soon.
Good luck,
Dave
1. Most of the time without a magnifier, bad solder connections can't easily be identified.
The OP should at least re-solder (clean & re-solder) the problematic ignition driver
connections since the ECM is open and retry the ECM.

2. If that doesn't solve the no start, then Pelican Parts also provides a rebuilding service.
Since this forum has helped the OP troubleshoot thru the 4+ pages of posts and neither
of the two mentioned provided any until the last pages, surely Pelican Parts should be
considered.
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Last edited by mysocal911; 03-20-2017 at 04:38 PM..
Old 03-20-2017, 04:35 PM
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Quote:
Originally Posted by scarceller View Post
For what it's worth I'm seeing a lot of ignition circuit failure issues in these DMEs, they are over 30 years old and have seen a lot of vibration. It's very possible this is a ignition circuit failure.
Yes, most definitely the driver circuit has a problem as shown here:



The rare, but occasional driver circuit failure occurs when the vehicle's battery is reverse jumped
for starting or the alternator was over charging (usually an intermittent occurrence).
In both cases, the power transistor is usually destroyed.
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Old 03-20-2017, 04:46 PM
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Quote:
Originally Posted by mysocal911 View Post
1. Most of the time without a magnifier, bad solder connections can't easily be identified.
The OP should at least re-solder (clean & re-solder) the problematic ignition driver
connections since the ECM is open and retry the ECM.

2. If that doesn't solve the no start, then Pelican Parts also provides a rebuilding service.
Since this forum has helped the OP troubleshoot thru the 4+ pages of posts and neither
of the two mentioned provided any until the last pages, surely Pelican Parts should be
considered.
Dave,
The Pelican rebuilding service costs $540, flat rate(?). The OP may not have soldering skills, yet all he might need done is a resolder of three connections. $540 seems kind of steep for that. If it was me, I would at least call around to see what are my options, such as a bill that includes an inspection fee and price for specific repairs needed. Loyalty to Pelican is great. But...
Dave
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Old 03-20-2017, 05:04 PM
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Quote:
Originally Posted by DaveMcKenz View Post
Dave,
The Pelican rebuilding service costs $540, flat rate(?). The OP may not have soldering skills, yet all he might need done is a resolder of three connections. $540 seems kind of steep for that. If it was me, I would at least call around to see what are my options, such as a bill that includes an inspection fee and price for specific repairs needed. Loyalty to Pelican is great. But...
Dave
Given your forum posts, you seem to be skilled enough to do some basic soldering, right?
With your guidance, you guys should easily be able to at least make an attempt at soldering.
Any questions, Google and youTube are your helpers.
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Old 03-20-2017, 05:18 PM
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Having met the OP today, I found him to be very competent, and he may well choose to try some resoldering himself. I also wouldn't be surprised that he sent it off for the work. If it were my ECU I might well try to do some of that work myself, but it is another thing for me to "give it a shot" with the unit of someone else.
We'll soon see what happens,
Thanks,
Dave
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Old 03-20-2017, 05:39 PM
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Many thanks to Dave M. for kindly letting me test my ECU in his (lovely '84) Carrera. And, once again, many thanks to everyone who posted on this thread, getting me this far and initiating me into the intricacies of Motronic troubleshooting.

On the advice of several people here, I asked Sal (scarceller) to take a look, and he's graciously agreed.

I was tempted to have a go at the soldering myself, but I thought it better to give it to someone who knows what they're doing (my soldering experience is confined to simple electrical (not electronic) connections, and my technique could use some improvement).

As for Pelican's rebuilding service, I do feel a loyalty to Pelican for making this site available. But I do buy all of my Porsche parts here (and some for my vintage bimmer as well), so I don't feel like I'm free-loading. And, yes, their flat fee is fairly steep if all it needs is touching up some cold solder joints.
Old 03-20-2017, 06:36 PM
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Quote:
Originally Posted by DaveMcKenz View Post
Having met the OP today, I found him to be very competent,


Quote:
Originally Posted by Hnichols View Post
Many thanks to Dave M. for kindly letting me test my ECU in his (lovely '84) Carrera. And, once again, many thanks to everyone who posted on this thread, getting me this far and initiating me into the intricacies of Motronic troubleshooting.

On the advice of several people here, I asked Sal (scarceller) to take a look, and he's graciously agreed.
Please remember to post the findings and pics of the damaged area for the benefit of this forum !
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Old 03-20-2017, 07:56 PM
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Quote:
Originally Posted by pmax View Post

Please remember to post the findings and pics of the damaged area for the benefit of this forum !
That would have been a good idea while the unit was open, i.e. a closeup picture of the three connections
of the ignition driver.
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Old 03-20-2017, 08:17 PM
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I'm pretty sure Sal will provide the findings.
Dave
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Old 03-21-2017, 03:56 AM
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