Thanks to all for your comments. And to Pico for their products and forums.
Some quick responses:
David Paterson- Interesting! You clearly have a pretty good understanding of the function of the electrolytic capacitor, which I suspect gives you a certain advantage of many of us! Would you like to share with us: a) How you spotted the 3 failed electrolytic capacitors; b) what caused their failure? This isn’t
>>Yes, I have a background in electronics. Electrolytics are common failure points in electronics. I think a typical failure mode in this application is temperature cycling which degrades the can’s seal, allowing the corrosive electrolyte to leak out. Corrosion of the cap’s leads or the circuit board are easy to spot.
http://en.wikipedia.org/wiki/Electrolytic_capacitor
James- In the photo of the ecm, can the failed parts be identified?
>>One cap is in this picture, the large blue can. Note the corrosion where the left lead is soldered to the board.
Will- What is a snubber?
>>Coils store energy during operation. When the circuit is opened a snubber provides a path for the energy to dissipate, protecting the switch or controlling circuit from a voltage spike (which can cause arcing at a switch).
http://en.wikipedia.org/wiki/Flyback_diode
—How do you know that a capacitor was bad?
>>All 3 showed signs of leakage, one measured low capacitance on a DVM. I changed all 3.
—You did not mention if you checked the MAF sensor for contamination.
>>An internet search suggested Ford MAF sensors are subject to contamination, resulting in degraded idle. “Goodâ€Â, I thought, “this will be an easy fix with the magic MAF sensor spray from the local parts storeâ€Â. The sensor wires didn’t look too bad, but I blasted them with the spray and hoped for the best. No change. Ford has the maintenance cycle built in- cooks the wires to burn off contamination.
James- Nice work, but did the Pico really expose the problems or was it the last resort to go to the computer.
Just a thought. still, nice call
>>Couple of things. At first I didn’t think I could get out the ECM without removing the AC dryer (and opening the system). So I kept looking for another cause. When it was down to something either inside the tranny or inside the ECM, I chose to make another attack on the ECM. It was my lucky day when I discovered I could pull the ECM out (behind the interior glove box) without making changes on the engine side of the firewall. I briefly considered (a few nanoseconds) troubleshooting the ECM with the caps in place, but I didn’t have a schematic nor any easy way to operate the ECM on the bench. The scope would have been necessary on that quest.
If I had known how to remove the ECM early on I would have solved the issue much earlier. Without the scope and not knowing how to extract the ECM, I might have submitted to changing out numerous other components, all to no avail. The scope was instrumental (duh) in getting the problem down to 2 possibilities.
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