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DME Repaired w/pics

Old 11-24-2010, 12:56 AM
  #46  
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Outstanding, glad I could help! Haven't seen your around here lately, hope all is well.
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Old 11-24-2010, 12:57 AM
  #47  
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Your multi-year old post is about to help a beautiful survivor 86 951 out here on the east coast, too
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Old 11-24-2010, 01:04 AM
  #48  
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This issue was the most daunting and most frustrating I've faced in my 6+ years of owning this car. Intermittent electrical issues just suck, period. That's why I went to the effort I did to document the fix so others could avoid the same issue and to pay back some "Rennlist points" I owed from all the help I've received here.

Motor on.
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Old 05-21-2011, 06:33 PM
  #49  
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Consider this the thread that keeps on giving ...

My son's '87 924S uses a 944 DME. His car has intermittently been dying for weeks and I've replaced spark plug wires, coil wire, cap/rotor, tested and cleaned crank/speed sensors, grounds, etc to no avail. When I was driving it recently, it died again and I reached under the dash and smacked the DME (not under the seat as in 944) and the car came back to life. I wasn't about to resolder the entire DME, so I found your post and resoldered the points you specified even though I couldn't see any cracks. It's been two weeks now and the car is finally running like a charm again. THANK YOU!!!
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Old 05-21-2011, 08:31 PM
  #50  
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Originally Posted by VWaddict View Post
I've been a professional service engineer for almost 30 years, and while it IS preferable to remove all old solder, it's by no means essential.

The important thing is that the solder joints are not dull and crystalline-looking (which is usually caused by the pieces moving as the solder cools through it's "eutectic region" -the transitional stage as it cools from a liquid to a solid.) when you've finished.

Basically, if the joint looks shiny and isn't 'balled-up' away from the circuit board or away from the component lead -i.e. it's clinging nicely to both- then it's a good joint. -If the old joint 'hisses and pops' a lot as you melt the old solder, it was porous and has moisture in it. -You should remove it, but as long as it boils off, you'll probably get another 10-20 years out of it once you add the new solder.

More info with pictures is here: http://dragon.herts.ac.uk/~eleqdml/t...eral/soldering

As regards not overheating the transistor, -yes that's true but that transistor can take a fair amoun of heat (it gets hot during regular use, hence it's being mounted to a heatsink) and it also has long leads, but still it's best to be mindful of not keeping the iron on the joint for more than ten seconds between cooling periods.

As a rule, these types of 'crack-line' joint failures occur at places where there's a lot of un-relieved stress or flex on the leads. Often a dab of "hot-snot" plastic glue-gun goo to strengthen or reinforce the mass of the component or heatsink at the corner where it meets the circuit board will help prevent re-occurence.

Keith
I'm with you . I was a bench tech until most consumer electronics became disposable . I found that flux-core solder will easily blend with existing solder , and as a matter of fact I usually have to add fresh solder to get the old stuff to melt before I hit the connection with the "sucker" .
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Old 05-22-2011, 01:21 PM
  #51  
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Originally Posted by pmooradian View Post
Consider this the thread that keeps on giving ...

My son's '87 924S uses a 944 DME. His car has intermittently been dying for weeks and I've replaced spark plug wires, coil wire, cap/rotor, tested and cleaned crank/speed sensors, grounds, etc to no avail. When I was driving it recently, it died again and I reached under the dash and smacked the DME (not under the seat as in 944) and the car came back to life. I wasn't about to resolder the entire DME, so I found your post and resoldered the points you specified even though I couldn't see any cracks. It's been two weeks now and the car is finally running like a charm again. THANK YOU!!!
Most excellent, very glad to hear this worked for you. It's been ~5 years since I originally posted this and my car is still running strong.
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Old 05-17-2012, 01:22 PM
  #52  
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Well, I opened the DME tuesday 5-15-12 night and made the repair, the transistor had a second solder joint at the 90 degree bend which looked suspect which was repaired also, The same tip metioned earlier it was not until I added a little solder did it seem to flow. Well I drove it wed. night after work seemed to idle better than before also. Had no issues, Drove to work to day no issues. I can now only hope that in five years I can say the same...LOL thanks for the reply and thanks for your help...
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Old 05-17-2012, 03:36 PM
  #53  
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Mine's still good 5 years later.
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Old 05-17-2012, 08:23 PM
  #54  
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Excellent news! Very glad it (fingers crossed) worked for you. It'll take you about a month before you actually believe it, lol.

Cheers!
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Old 05-18-2012, 03:20 PM
  #55  
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Good write-up. I will be storing this in the back of my brain for later use.
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Old 07-19-2012, 07:21 PM
  #56  
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Just an update for anyone else with issue after soldering the ECU car had no issues for about a week. Then again no start, no tach movement...I went through a check list of every thing I done new sensors LR wireing harness ECU solder. And then it hit me, when I replace the motor I just moved the sensor bracket from blown motor to Ebay motor. And never checked the gap. since it started up I always assumed it must be close..Oh it was off way off. the gap was set to the .08mm and has been rock soild ever since. Thank to all the input..
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Old 03-23-2018, 06:09 PM
  #57  
Laust Pedersen
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Default 951 Dying Randomly

One morning 2 months ago the engine just stopped running without any warning just half a mile from home. The engine showed no life at all during multiple starting attempts and everything else seemed to work including tachometer bounce. After the starting attempts, there was a strong smell of sulfur from the exhaust, which I attributed to the new converter and fuel not getting ignited ů towed home.

The next day I tested for spark with a 5th plug (being visible during starting attempts) on the 4th sparkplug wire. Nothing for the first 4 seconds, then sparks and the engine started on 3 cylinders.
So all appeared good until another morning 3 days later where the engine died again, fortunately near a gas station where I could just cruise into a parking spot, then open the hood, yank on the low voltage ignition wires and for good measure a slap on the passenger foot board, behind which the electronics and too many wires reside. Low and behold, the car started and lasted long enough to get home.

A few days later (at home) the car wouldnĺt respond to multiple start attempts, which is a good thing for fault finding. On the first root cause fault finding attempt I focused on the coil, which measured out to have no open posts (i.e. probably good).
Next I focused on the stuff behind the passenger foot board, cleaned, sprayed and reinstalled the big connectors without any improvements. Then focused on the DME and gave that a slap and miraculously the car would now start.
Fortunately I had a spare DME, which I swapped in after transferring the EEPROM and once more the car would start, so I made the swap more permanent by including my custom fan cooled DME back plate and closed up the area.

The car has continued to start flawlessly since, but it would be nice to once more have a functional spare DME, so I searched on the forum for "DME repair" and found this thread. Sure enough my bad DME had exactly the same symptoms and problem as describe here. So after re-soldering the three transistor connections, I should now once more have a fully functional backup DME.

So thanks Greg for this write-up.

Laust
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Old 03-23-2018, 06:59 PM
  #58  
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Fantastic, glad it helped you out Laust. Funny, I was just thinking nice things about you yesterday as I was admiring your vacuum port in my car.

Well done sir!
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Old 12-05-2018, 04:15 PM
  #59  
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I'd like to add my own success story... after misdiagnosing a broken fuel pump for an intermittent stall, I stumbled on this thread and did my own little soldering.

My DME's same joints pre- and after- soldering:







Plus, I noticed similar lines on most of the joints attaching the pin ends:





I re-soldered these too. On my second day driving to work, the issues haven't recurred. Great thread! Thanks

Last edited by Dan Martinic; 12-05-2018 at 04:16 PM. Reason: Spelling
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Old 12-05-2018, 05:21 PM
  #60  
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Good work Dan and thanks for adding the additional pics.

It's been 12+ years(!) since I did this repair and it's still running strong.

Greg
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