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ANSWER 92 940 Periodically Stumbles & Won't Drive Faster Than a Crawl! 900 1992

posted by  spook on  Sat Jan 25 22:34 CST 2014
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last visit: Fri Oct 24 08:06 CST 2014
[RELATED]

Dear semv940,

Hope you're well. A nephew has a '90 760 (with B230FT engine). He reported very similar symptoms. He traced them to the Engine Control Unit (ECU), which is mounted behind a plastic panel, on the door-side of the passenger footwell. More specifically, after he re-flowed the solder joints on the ECU circuit board, the problem went away.

Re-flowing the solder is tedious. You need only keep the tip of a 15- or 20-watt soldering iron on each connection for only 1-2 seconds. That's all required to cause the solder to liquefy. When that happens, the solder changes color, from a dull gray to a shiny silver.

Over time, solder joints fail - they develop micro-cracks - because of repeated heating and cooling cycles. These micro-cracks are far too small to be seen with an unaided eye.

It should not be necessary to add solder. Adding solder to very tightly-packed connections means risking joining things that should not be joined.

But taking the time to reflow the solder on the ECU circuit board seemed to cure his car's intermittent refusal to run at full power, until it was shut-down and re-started.

Hope this helps.

Yours faithfully,

Spook

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