1987 Buick Grand National ECM pin identification

[Nowuffo]

Greetings,

I have an 87 Buick GN, ECM# 1227148 that I am trying to find information on the two connectors inside the casing.

The connectors are labeled CONN C1 and CONN c2 at the lower right of the attachment.

The connectors are used by some aftermarketvendors and can speed up transmission of data from 1.5 to 8 times a second...yet there doesn't seem to be any data for what the pins actually do...and which ones.

Any similar GM ECM's with these connectors and/or dat to go with?


Stymied and curious about what they do.

Any ideas?

[Holden202T]

those two connectors are the plugs that connect the engine wiring loom to the ECM ?

in the top of the diagram all the connections with labels a/b/c/d are to those two connectors .....

I believe they are just in the diagram to show you which pin goes where on the plugs ?

[Nowuffo]

The ECM harness connections are separate from the two connections I am curious about.

I have attached a pic with the ECM harness connector boxed in yellow, with the two "shady" connectors boxed in green.

Thanks for the reply

[Holden202T]

i don't believe the connectors in the green box are the right ones, look at the connectors on the diagram, too many pins in the smaller connector to be that smaller connector in the green box.

I am not sure what the green box ones are, some sort of factory programming port maybe ... our Australian 808 computer has them too, never been used for anything that I know of though.

[VL400]

Exactly what Holden202T said. The connectors C1 and C2 are what you have circled in yellow. In your wiring diagram it has the letters A and B below C2 and C and D below C1. So C2 has the pins A1 to A12 and B1 to B12. C1 has pins C1 to C16 and D1 to D16.

The green connector circled is likely a breakout of the data bus and a few other things. It wont be in any GM wiring diagrams as it was only used in the factory and/or during development. Some aftermarket tuning and logging options use them (they appear on a number of different Delco ECUs), but you would need to reverse engineer them if there is nothing online showing the pinout and then develop hardware to suit.

[Nowuffo]

Thanks for the replies.

I see the logic now in the number of pins vs. the actual connector.

Time to hook up the scope.

[timekiller]

I was just searching for some info and came across this. Felt compelled to perhaps help because I think I know the answer. Maybe yourself or someone else could still benefit from my knowledge of this space.

Many ECM's have one or both of those connectors. The 1228079 ECM in the 1987 and 1988 Monte Carlo SS has the 40 pin connector, not the 12 pin one.

My 40 pin connector is about 95% similar to this one:

Notable differences between that schematic and the 1228079 are IRQ1 is on 38 and not 4, and the schematic does not show that 35 and 36 are both +5V, at least they are on the 1228079.

You don't need a scope to validate it, just a multimeter with a continuity test. Just put one lead of your multimeter on the pin of the connector, and the other on the matching pin number on the CPU - the chip marked 16021633 in that schematic, and on your ECM board. That's how I validated mine, and found where IRQ1 actually was on mine vs. that schematic. Before you test anything, you're going to need to scrape away the plastic-y coating on the board where those pins are, and a little on the CPU pins, or you won't get a connection to your meter leads.

I'm currently building a project that does essentially what you are asking. But I'd have to warn you, the approach I'm taking is quite involved. I'm not sure there is an easier way to go about it that would actually work though. It involves converting the old 1K or 4K PROM to a 64K EPROM, redirecting the chip select from the ROM to the PROM for the program code, and adding an interrupt routine to the code to copy the data over to a dual port SRAM chip where it can be read by another device. If you are still curious, you can poke around the forums on montecarloss.com to find my posts to date. I have yet to write up the final part where the 40-pin port is used to get the data out, the only bits I've written so far are the parts about converting to a larger EPROM and redirecting the chip select so that the code can be modified.

http://www.montecarloss.com/community/u ... er=1028577

In order to consider modifying the code, you need to find a disassembly for your ECM's code, then massage it until you get it to assemble through ASM11. It looks like your source is available here:

http://gearhead-efi.com/gearhead-efi/mo ... ks/31T.zip

but it's quite far away from being assemble-able. It would take at least a day to massage that file to get it back to where you could throw it through an assembler and get a binary that could be burned to a 64K PROM.

Anyway, I do hope that helps, if nothing else to demystify things a bit.

Greetings,

I have an 87 Buick GN, ECM# 1227148 that I am trying to find information on the two connectors inside the casing.

The connectors are labeled CONN C1 and CONN c2 at the lower right of the attachment.

The connectors are used by some aftermarketvendors and can speed up transmission of data from 1.5 to 8 times a second...yet there doesn't seem to be any data for what the pins actually do...and which ones.

Any similar GM ECM's with these connectors and/or dat to go with?


Stymied and curious about what they do.

Any ideas?

[timekiller]

Just to complete my response above:

I wrote up a thread on montecarloss.com describing the use of the 40-pin ECM connector by an Arduino microcontroller using a Dual Port SRAM as a memory buffer. Link here:

http://www.montecarloss.com/community/u ... ost1031177