How the 4A-GE ECU works

[JMR_AW11]

Red Wrote:Where have you folks been hiding.<G>

A thought on why there are two boards joined by a ribbon cable: Back then, some of the Japanese electronics companies, including the big ones, sent work home to cottage workers. They might send home 100 people, each with six baskets of parts, and expect to get back 600 alternators the next morning for that famous "just in time" zero-inventory production. In a situation like that, for small parts runs, I could see separate circuit boards going home in the basket to be hand-soldered to the ribbon cable during ECU assembly. Odds are it was this or a similar mundane production reason.

Much of the electrical system (ignition and charging both) on these cars was semi-primitive for the time they were built, about 10-15 years behind many GM domestic products. Like using a cap and rotor, instead of a reluctor assembly, and an alternator with wide (loose) regulation. And using the same exact type of wire for both the alternator output, and battery voltage sense leads. Wasted on one, too thin on the other.

Not sure I agree that the Denso ECUs are primitive.
I believe they went to great lengths to make these ECUs as custom and reliable as possible.

A casual glance at a 1985 4A-GE ECU might make you think these ECUs are primitive as they use old fashioned through hole components (no surface mount).

But if you look closer you will see some big tall black plastic custom ICs with labels like "ND HC120"

These hybrid ICs are made by Denso themselves and if you take one apart with a scalpel you will find they contain a little ceramic circuit board with thick film technology with SMD as well.

This is very advanced technology for the early 1980s.

No waywould Denso allow their ECUs to be assembled by semi skilled workers. These ECUs will have been built under strict quality control to ensure reliability. They are extremely well engineered for long term service. Take a good look at the quality of the soldering on these ECUs. It is very good indeed and I would guess it was done by a machine.

Here we are over 20 years later and these ECUs are still performing well despite having been exposed to the shock and vibration from the car chassis for maybe 150,000 miles.

Here's an image of a Denso hybrid IC using film and SMD technology.

This kind of explains why these ECUs were so expensive if bought as a replacement from Toyota.