I'm trying to learn more about the inner workings of GM's ECMs, and I noticed the 1227165 appears to only have one A/D converter versus the 1227730's two. Is this correct, and if so, why? Some of the inputs for the '730 seem redundant, such as TPS2, MAT2, MAT3, etc.

Judging from the presence of a separate A/D chip, it seems like the 68HC11 used doesn't have any internal converters. Why did GM opt to go this route?

Here are links to both schematics:

1227165

1227730

 

Seems everything in these ECMs are done by "chip select" operations due to the limited number of channels/ports on the processor itself. Best guess would be that it is easier to develop expanding/contracting designs as needed without having to have a large base unit in apps that didn't need all the I/O. Each channel is read in as needed by the chip and channel.
This thread from the Tuning guide has some real good info on the usage of the mux channels on the 730 to take advantage of the expansion A/D.
https://www.thirdgen.org/forums/diy-...ml#post2150901

EGR position and knock sensor inputs seem to be the reason the second set was needed. Just ran out of inputs it seems.

 

That thread on the '730 is actually what made me curious about the A/D .

What you said about changing designs makes sense, though. Thanks!

 

I thought a stock 730 ECM with $8D doesn't use the EGR ON switch input?

I think the main reason the 730 came about was it was more universal. The new ESC / PROM provided more protected / reliable ckts.

Overall, it was a MAJOR improvement over the 165. It allows the use of the EGR ON switch to be moved to the single bit ON/OFF inputs of device U13. All the unused A/D inputs allow for the current setup I am running.......3 IATs, 1 exhaust back pressure sensor, 3 toggle switches, WBO2 input, Exhaust temperature input....and outputs like wastegate control, second coolant fan control, water/alky pump control........all that with stock AIR stuff available. The only thing missing is a PWM output for an E-trans.

EDIT: I looked at what it would take to run 730 $8D code on a 165 ECM last Fall. The 165 ECM has enough hardware. It would probably take a couple of months to change the $8D code I/O addresses and routines to run on the 165 ECM. A bench setup would be required. If it was done that way, the MAF guys could swap to $8D when going with boost units with almost no trouble.

 

It doesn't but my searches have shown it was used at A3 on something for EGR position. Analog reading rather than an on/off. Don't see in my notes where I came across that though.

That's alot of extras you have running.
What did you do about the pull ups to make the inputs read correctly?
I'm thinking about scratching them off myself after building buffer amps to isolate them with no luck. My EGT just won't cooperate on any input with the pullup on it.
B3, F11 in particular have me wanting to do surgery.
Havn't tried B7, E10, F12 & F14 yet. Figuring more of the same.
E11 looks interesting.
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Hey,
Those are getting harder to find around here as it is. If the boost code ends up working and MAF code goes in then everyone would want one

 

None of the schematics I have show the EGR ON switch going to an ECM for the 730 stuff. Since the latest project is a 165 ECM harness to 730 ECM conversion and the wire was there I stuck it at pin D2 or D3. Never hurts to have extra stuff to play with.

Yeah, I got out of control with the extra sensors. This stuff is usually just a science project for me. All of the extra wiring was a PITA. Some of the pull-ups were tweaked and some of the tables were created using resistors in place of the sensors.....sometimes a little heat on a stock sensor to cal the table. I picked up some junk turbos and a couple of junk intercoolers so the extra IATs are for measuring effieciency. The exh. back. pressure is for measuring turbine A/R, exh. manifold, mufflers, and cam efficiency.
E11 scares me. Although, some sort of second NBO2 sensing comes to mind for it.

165 ECM are getting harder to find? I always had trouble with freeware ALDL tools and 8192 baud locking up. I have wondered if it is due to the 165 ECM code itself. It has been a long time since I looked at the $6E. Not sure if adding a MAP routine (it has the hardware for it) would be easier than the $8D conversion. I like the 730 so much better that I dropped the 165 ECM w/ $8D code idea. I think my efforts are better spent playing with the 427 ECM at some point. Although, not much coding has been going on lately.......most steel & alum. fab. stuff. Playing with the TIG can be a lot more fun than writing code.

 

The 730, was an engineering exercise at GM. It was an attempt to have the most universal ecm (within practical limits) possible. At the time of it's design it was ward winning.
The 165 was just the opposite, ie used only a 1/2 PCB, and was just enought to get the job done. It from day one had issues, most notibly, not having enough solder holding things together.
The interval between the two were millions of cars, and billions of miles.