Types of GM ECMs

[Ludis Langens]

bruce plecan <nacelp at bright.net> wrote:
> All the C3 types use a 2732 style prom, and 2 connectors.

(I'm ignoring any carb ECMs and the old TBI ECMs with throughhole
resistors/capacitors.  There doesn't seem to be any sense in going back
that far in history.)

No on 2732, yes on 2 connectors.

The 83-86 2.5 L4 TBI & 84-86 1.8 L4 TBI use an ECM with a single circuit
board, no resistor pack, a TMS2532 EPROM, and two edge connectors.

It looks like the 84 2.0 L4 TBI and maybe 84 1.8 L4 turbo have a
daughterboard ECM with a resistor pack, N82S181 PROM, and two of the
dual row pin connectors.

The more recent C3's all seem to have daughterboards, resistor packs,
2732 EPROMs, and the two dual row pin connectors.

(I haven't actually seen a '747 and assume it is of this last style.)

> All the P4 use a memcal/calpak, use 27128/27256 proms, 
> and 3 connectors.

The 1227748 (used on various L4 TBIs 1987-??) is certainly a P4 but uses
a (bare) 27128, no resistor pack, and has two edge connectors.

And then there's the underhood P4 with four connectors.  I haven't seen
one of these either.

> Are there other GM EFI series?.

Cadillac?  Saturn?

> Is the prom holder/memcal.
> connector an accurate way of id ing them?..

Here's what I've observed so far:
  Surface mount (SMD) resistors and caps, throughhole DIPs ==> C3
  SMD resistors, caps, and ICs ==> P4

               unsigned long BinToBCD(unsigned long i) {unsigned long t;
Ludis Langens     return i ? (t = BinToBCD(i >> 1), (t << 1) + (i & 1) + 
ludis at cruzers.com            (t + 858993459 >> 2 & 572662306) * 3) : 0;}