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Re: Ignition computer woes

   I am in the middle of trying to resurrect my 83 TQC.
   The ignition computer hasn't worked for some time. 
   There is some small chance the time belt is off by 180 degrees.
   I had a broken arm and lost a water pump.  So I had the local
   shop do the belt as well. It never ran right afterwards.  They

At the risk of repeating some of what yoy already know...

There are three "timing" signals used by the ECU - flywheel, "TDC", and
"Master TDC" (my names; don't remember what the manual(s) call them).

The "Flywheel" signal is 135 pulses/revolution of the engine. This sig-
bal comes off of the flywheel ring gear.

The "TDC" pulse is once per revolution of the engine, at 60 degrees BTDC
for #1 cylinder. This signal also comes off of the flywheel, triggered by
the "index pin".

The "Master TDC" is once every other revolution of the engine, and syn-
chronizes the "TDC" with #1 cylinder intake/compression/firing stroke.
This signal comes off of the distributor.

So -- first thing, hook up a timing light to any ole plug wire -- if it
fires, the ECU is working (well, triggering the ignition, anyways).

If no spark signal, does "Master TDC" overlap "TDC"? If so, then you
have $erious problem$. If it doesn't (easy to see if you have a dual-
trace scope...), then your engine timing is all f*****d up. I'd start
with verifying #1 TDC, then timing belt to cam to distributor (and if
you're lucky, index marks on the flywheel...). I believe it is possible
(and in fact downright easy) to get the distributor off by a tooth or
two, which is sufficient to cause the whole system to fail. I think you
can't get the distributor off by 180.

Good luck.

I'd try for another UrQ and swap ECUs (what a pain...but a smaller pain
than just about any other option...)

   and all of the reference signals show up with a scope.  I traced
   the ICU firing circuit back through the ICU till I hit unknown
   chip pins.

Wouldn't happen to be that xxxx'ing HD46506 chip by any chance? If you
can find any data on that chip, there are several VERY INTERESTED par-
ties who would also like to know about it. Hitachi has been less than
cooperative with *my* efforts to extract information from them...maybe
you can find a bigger hammer inside JPL...and if you actually find a
source for them, *I* am *VERY* interested in acquiring one (since I've
got a dead ECU and I'm 99.95% certain it's that damnable 46506 chip)!!