"a whole circuit board should not actually cost more than a few $" Well, it depends how few dollars you are talking about. Even in significant volumes, a quality blank PCB with 2 or more copper layer by itself costs more than a few $. Add to that the number of individual parts, some of them priced at a few cents and others several $. Then you have the assembly time, the testing and qualification time, the amortization of the often pricy test equipment and of the development time. Then add a bit of profit and you'll soon find that tab can realistically exceed a $100 at the production level. With the additional shipping cost, dealer inventory management and mark-up,you can reasonably expect that the complete, operational PCB assembly will in turn cost you significantly" more than just a few $".
I think you may have that reversed. My recollection is that Ford decided to OEM Mazda small trucks instead of developing their own small truck. Instead, Ford put their development money into their popular F-150/F-250/F-350 medium size utility trucks.
ECMs were new technology in 1991 and the lesson of potting ECMs (presumably to reduce component lead flexing, to reduce moisture infiltration, to distribute heat better, to make it harder to change the microprocessor firmware, and to keep fingertip electrostatic generators away from the ECM circuitry) had yet to be learned. The electrolytic capacitors in my 1991 Mazda B2600i ECM were radial-lead parts and vibration might have contributed to the component failure I described.
I am most impressed that you were able to replace the failed caps. My experience with the Chrysler brand has been that things were encased un a urethane-type potting filled with sand. Very hard to remove and impossible to see through. But they may have changed things by now. The very hard, sand filled potting certainly did make both alteration and repair very challenging.
Another point here is that capacitors degrade fairly predictably over on time. Many electrolytics will overheat slightly and push their lids out to a slight dome. I have fixed many older machines just by looking for this.
A friend bought me a T shirt with the logo "I void warranties". If one has a good grasp of the principles on which systems work, the possibilities are almost endless. Engine injector pumps are supposed to require specialist servicing, but there is no magic about them. Just use a very clean bench, and a gentle touch.
Manufacturers should take far more responsibility for defects though, even far beyond warranty.
What a great story. How many consumers would end up changing a capacitor on the ECM? Even among engineers, I would think the percentage would be very small. The kicker is that the truck is still running well 12 years after the fix.
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