[Gmecm] $6B, $8B, $A8 for 1228707 or 1228708 to control Cadillac Northstar

[William Lucke]

This question also applies to:
$5C for 1227749
$CE for 16156450
$E8 for 16173278

I've worked with a guy (who may be subscribed to this list) to adapt $A1
in a 7730 (originally '91 3.1 DIS) to run a '93-'99 Cadillac Northstar
with 8 cylinder DIS.

There are a number of ways in which the $A1 is not appropriate to this task:
-VE tables go to ~4500 RPM while the Northstar revs to 6700
-Primitive BLM layout only has "idle" and "off-idle" BLM cells
-RPM/25 datastream location can only report 6375 RPM
-Others I'm probably forgetting right now.

To overcome the last, he implemented an RPM/35 variable and dropped it
into the datastream in the location occupied by EGR position. This allows
RPM reporting up to 8925.

The Quad 4 was GM's roughest and tumbliest engine of the late '80's and
early '90's, being roughly equivalent in state of tune to the 195 HP 2.3
litre S14 used in BMW's E30 M3 from '87 to '91ish.
The code masks and ECM's listed above and in the subject line were used
with Q4's, according to Tunercat.

What's the ending RPM for the VE tables in these masks?
What's the BLM structure? (IE, 16 cell like $8D or 2 cell like $A1 or
somewhere in between?)

What sort of extra I/O do the 8707 and 8708 have?
How does the triggering of the Q4 ECM work? Does it read the crank sensor
signal directly, or is there an ignition module which reads the crank
sensor and outputs a 0-5V signal as with the V6 engines?
I @$$ume the 8707 only has a single ignition output and the ignition
module takes care of ignition distribution.

Starting with a code mask that has VE tables that already go to a pretty
high RPM would help out a lot with tuning a Northstar, as would a 16 (or
more) cell BLM structure.

Thanks!