DME Relay - Failure and Repair
07-21-2011, 12:25 PM
#17
Race Car
I had a weird experience last year. My DME went bad (seemed to be the original) while in my garage. No biggie, swapped it out and I was on my way. (Ironically two of my local buddies went out the same week - hot weather related?)
The weird part was that a few months later I blew another DME. I was doing some hard driving in the CO mountains and stopped at Independence Pass for a hike. I had time contraints as I needed to pick up my kids from camp in Aspen - 25 mles away. Finished the hike and came back to the car - no start. A crowd gathered (blushing). I pulled my DME and it had blown with melted plastic and black burn marks. Wow, it really went! Fortunately, I replaced the DME and was on my way.
I now carry 2! spares. But I was surprised that it somewhat "blew up". Must have really heated up the fuel pump? No issues since.
The weird part was that a few months later I blew another DME. I was doing some hard driving in the CO mountains and stopped at Independence Pass for a hike. I had time contraints as I needed to pick up my kids from camp in Aspen - 25 mles away. Finished the hike and came back to the car - no start. A crowd gathered (blushing). I pulled my DME and it had blown with melted plastic and black burn marks. Wow, it really went! Fortunately, I replaced the DME and was on my way.
I now carry 2! spares. But I was surprised that it somewhat "blew up". Must have really heated up the fuel pump? No issues since.
07-22-2011, 12:11 AM
#21
Rennlist Member
Thread Starter
Your DME relay and circuit board may have cold solder joints at other points.
I even had to use a solder sucker to remove some of the existing solder and redo some of the solder points with flux and fresh solder.
My original DME relay is not ever going to fail due to solder issues.
07-22-2011, 08:21 AM
#23
Rennlist Member
Nice job Alex! I can appreciate your troubleshooting and repair.
07-22-2011, 12:07 PM
#25
"Did you open it up to see what caused the failure?"
VIBRATIONS!!!!!!
Read here under 'Vibrations' for more info:
http://www.systemsc.com/problems.htm
VIBRATIONS!!!!!!
Read here under 'Vibrations' for more info:
http://www.systemsc.com/problems.htm
07-22-2011, 12:18 PM
#26
Rennlist Member
Thread Starter
Vibrations caused "melted plastic and black burn marks"?
I can see it causing a problem with a bad connection, but not the above.
In my case, it wasn't even "vibrations". It was the force applied to the casing of the relay to grip it for removal. It caused a cold solder joint to now fail and at best be intermittent.
I can see it causing a problem with a bad connection, but not the above.
In my case, it wasn't even "vibrations". It was the force applied to the casing of the relay to grip it for removal. It caused a cold solder joint to now fail and at best be intermittent.
07-22-2011, 12:29 PM
#27
"Vibrations caused "melted plastic and black burn marks"?"
Rarely if EVER occurs! Never seen one fail like that
in 20+ years working on many 3.2s/964s/993s
helping dealers and independents.
The majority of relay failures occur from cold solder
joints the result of vibrations, i.e. the wave soldering
method used in manufacturing doesn't allow for
adequate heat penetration of the relay metal for
the solder adhesion. In any other application,
e.g. home P.C., that soldering method would be
adequate but NOT in an automotive environment.
Rarely if EVER occurs! Never seen one fail like that
in 20+ years working on many 3.2s/964s/993s
helping dealers and independents.
The majority of relay failures occur from cold solder
joints the result of vibrations, i.e. the wave soldering
method used in manufacturing doesn't allow for
adequate heat penetration of the relay metal for
the solder adhesion. In any other application,
e.g. home P.C., that soldering method would be
adequate but NOT in an automotive environment.
11-05-2011, 04:12 AM
#28
Pro
Background:
According to the date code on the relay casing, this is the original relay that came with the car when it was manufactured back in 1995.
The relay performed flawlessly in the time I've owned this 993 and failed shortly after removing the relay from the fuse & relay board. The relay was removed in order to pre-lube the engine after a long winter layaway. This enables the starter to crank the engine over thereby building up oil pressure while disabling the fuel injection circuit.
Removing the relay from its socket in the fuse & relay board was enough to cause a break in an existing faulty connection on the printed circuit board.
....snip....
Solution:
The solder joints in the following photo were resoldered. The two solder joints within the yellow rectangle were the problem connections as the upper coil was intermittent when energized and only operated when pressing on the printed circuit board or side terminal (85b).
According to the date code on the relay casing, this is the original relay that came with the car when it was manufactured back in 1995.
The relay performed flawlessly in the time I've owned this 993 and failed shortly after removing the relay from the fuse & relay board. The relay was removed in order to pre-lube the engine after a long winter layaway. This enables the starter to crank the engine over thereby building up oil pressure while disabling the fuel injection circuit.
Removing the relay from its socket in the fuse & relay board was enough to cause a break in an existing faulty connection on the printed circuit board.
....snip....
Solution:
The solder joints in the following photo were resoldered. The two solder joints within the yellow rectangle were the problem connections as the upper coil was intermittent when energized and only operated when pressing on the printed circuit board or side terminal (85b).
I had exactly the same thing happen to me, original DME relay worked fine until I pulled it. Replaced it and fail... Re-soldered it and now use it as a spare. Even the same joints were bad!
11-05-2011, 08:36 AM
#30
Super Moderator
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Excellent write up.
Things like this have become more of an issue with the requirement for lead free soldering due to RoHS, started by the EU.
Lead free solder is more difficult to flow and requires higher temperatures and is prone to cold solder joint problems. It is a major PITA.
If possible, use the fashioned (lead) solder. Also using a flux dispensing pen can help with reflows.
Things like this have become more of an issue with the requirement for lead free soldering due to RoHS, started by the EU.
Lead free solder is more difficult to flow and requires higher temperatures and is prone to cold solder joint problems. It is a major PITA.
If possible, use the fashioned (lead) solder. Also using a flux dispensing pen can help with reflows.