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I have a 2008 Sport Trac with a dying PCM whose symptoms overwhelmingly suggest that it has one or more bad electrolytic capacitors. It's likely to be an easy repair... assuming I can figure out how to get the case opened without damaging it.

I "get" the general theme... use heat to soften the glue/sealant, then pry it apart... but the devil's in the details... like, "the temperature that's hot enough to soften it, without melting or warping the plastic connector shrouds". I need ideas for how to go about getting it opened up without damaging it.

Also... when I'm all done... what do I need to buy so I can re-seal it up the same way? It obviously won't do me a lot of good to fix today's problem, only to have it die "for real, and for good" 3-9 months from now due to moisture getting inside.

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  • Welcome to Motor Vehicle Maintenance & Repair!
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 19, 2021 at 19:23

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Rubber mallet and pry tools. Hammer the first one in at back corner and then just slowly pry them open going all the way around it. I have special pry tools I made but you can get it done with flat heads screwdrivers. I used to use heat but its only helps a little so not worth the extra effort and care needed for the hot case. The only detail you really need to be concerned about is to not damage your connectors or the pcb with your tools. I also advise you to only remove the cover and to not try and remove the pcb completely. Its sealed to the case (heat sink) with silicone adhesive and can damage easily when trying to remove. All the electrolytic caps are on the top side. The bottom side is mostly just logic stuff, mcu and flash.

To seal units when done I use permatex 81173. Its Oxime silicone. Neutral curing and not conductive so its safe for the electronics if it happens to spill out on them.

Not going to lie, If your thinking its leaking caps, I've never seen one on this style fomoco ecu and I repair ecu's every day. Mostly ford and chrysler group stuff.

What issue's are you having that make you think its bad capacitors?

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  • I've gradually had increasing problems with the same few sensors, all of which have been replaced to no avail (camshaft position sensor, throttle position sensor), plus OBD2 reports errors with them and the ADCs. Sometimes, everything is fine. Other days, the truck just goes completely psychotic & either won't start, or runs badly & stalls within seconds of starting. A mechanic confirmed the ECU is the root problem, he's just letting me take a stab at recapping it in case it solves the problem & avoids the cost of a new one (and its programming).
    – Bitbang3r
    May 19, 2021 at 19:33
  • This is also consistent with the way electrolytic capacitors tend to fail. They rarely fail suddenly and outright... it's more like, one day they start becoming randomly flaky, and slowly get worse and worse over time. The truck is also 12.5 years old, which is prime-time for electrolytic capacitor failure... especially caps that were used in hot environments (like the engine compartment of a vehicle roasting under the hot Florida sun). Given the extreme cost to replace it (even with a used one, after adding programming costs), I figured it's worth a stab at the caps first.
    – Bitbang3r
    May 19, 2021 at 19:37
  • Its not going to be cap problems. Maybe a logic gate failing or some type of liquid/moisture that sneaked in. These type of things are not easy to diagnose and repair on the bench honestly unless the conditions can be replicated while your working on it. Definitely worth opening up and taking a look at tho. The Sport trac pcm's are a bit pricey.
    – narkeleptk
    May 19, 2021 at 19:39
  • Would a logic gate failure show up intermittently, though? I'd expect that to be a "blue smoke" type of failure (magic blue smoke escapes, and it never works again), as opposed to "randomly crazy, occasionally sane". The failure was pretty insidious... I went for more than a year with maybe a crazy moment or three every couple of months, then the problems just started to manifest more and more often. Even now, with my truck being completely dysfunctional for hours or days at a time, it took the mechanic 3 days to finally "catch" it having a bad day.
    – Bitbang3r
    May 19, 2021 at 19:47
  • Underscoring the subtle wackiness, he started it up a few times per day for two days, it worked fine. He drove it to lunch on day two, it worked fine. He drove it to lunch on day three... it ran fine there... then went completely psychotic when he tried driving back to the garage, to the point where he had to tow it. That's part of the reason I suffered with it in that dysfunctional state for so long. It's hard to diagnose something that keeps pretending it's not broken. ;-)
    – Bitbang3r
    May 19, 2021 at 19:52

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