On 09/20/2013 09:23 PM, wrote:
> On Wednesday, September 18, 2013 11:47:23 PM UTC-4, jim beam wrote:
>
>>> Where is this located?
>>
>> crank, cam or distributor.
>
>
> I have a factory service manual, so far haven't found a mention of a
> TDC (top dead center) sensor. I don't think it's on the cam or crank
> since I don't recall ever seeing anything like a sensor on either -
> I'm guessing it's most likely on the distributor.

on an old distributor, each of the lobes was timed for each ignition
point, and that's what you're looking for here. depending on the type
of distributor it'll have a reluctor or other sensor with at least one
"pulse" generator for each of the four firing positions. [on your
4-banger.]


>
>
>> have you tested the icm yet?
>
>
> What's happened since I first posted this - while getting
> familiarized with the wiring to the ICM, I was nosing around, grabbed
> and jiggled the harness connector to the coil. Now the car fires up
> instantly every time and runs smooth as silk as before this issue
> developed. I can't say for a fact that's what did it but that's the
> only manipulation I did and it's been running without issue since.
> Maybe corrosion on the connector reached a critical point and was
> impeding spark?

more than likely. ignition electronics, with certain exceptions* that
are plagued by what become well known failures, are generally very
reliable. with the above caveat, it's much more likely that a problem
is a connection than it is for the electronics to actually fail.


>
> It's unclear from the previous input what I'm supposed to do to test
> the pulse from the ICM. Am I supposed to be able to use the inductive
> timing light to get a pulse from one of the ICM wires?

timing lights only get triggered by a high voltage spike like coil
output, not the low voltage that would be coil input/icm output. to
test the icm, you need to identify the individual leads mentioned
previously, and use a voltage indicator of some kind, like an led.



* a classic is the honda icm or "ignitor". the ones that shipped in the
late 80's civics have a very high, near 100%, failure rate and there was
a recall. the replacement units also failed, but less frequently.
reason is, not only are they mounted in an already hot location, they
had a convoluted and poorly conducted path for its heat sink. run too
hot for too long, semiconductors fail, and that's what happens. later
models used the same ignitor, but had it directly screwed to the
distributor wall for heat sinking which was much more effective. toyota
of course, did things like mount their unit well away from heat on the
inner fender next to the ignition coil.


--
fact check required