1226519 ECM 160 baud ALDL output

[Louis Baiani]

I made an adapter to read the ALDL info from the 1226519 ECM (closed
loop carburator control - CLCC) for an 84 Century.

With the ignition off, the data output is perfectly fine.  Once the car
is started, the data is fine for a short time, then it becomes garbled,
as in out of sync...enough to change all the values for that update
interval.  Some times the data stays fine for a few mins, some times
after a few secs.  Most likely will screw up when accelerating.  Not
alternator noise, because I took off the belt and/or connector.  I have
tried to filter with different supplies/chokes/caps to try to rectify
the problem.

Just today I thought again on what it could be.  The distributor was
never isolated, so I unplugged the 4 terminal HEI connector to the
computer.  I have found that this cured the problem, and the data is
perfectly fine.  Could it be a bad HEI module? (internal amplifier?)
Had anyone heard of this?  Should I use a scope to look at the signal?

I would also like to find ALDL info on an 84 Vette, 5.0L (L83 engine).
Please help.


Louis



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