The only access is underneath where the transmission has tow plastic
screens that pop out easily.

Inside there. I can feel the holes and there is about 2mm clearance to the
aluminum case. I put a pry bar in and bent it back into better alignment
with the screwdrivers supporting it from bending closer than 2mm

After some “adjusting” I could then put my fingers in the hole and feel the
ring with the holes passing as I turn the crank with a wrench ( distributor
and battery disconnected)

I could also cut a piece of wood about 2mm thick to slip in the gap between
the tin and the case.. if I can get it closer it might work

The actual TDC sensor i did swap out with my old one for a test but I could
do that again and spend more time getting it a bit straighter.


I know a little about encoders on modern machinery. for example one that
I worked with had 3000 pulses then one zero position
the computer could sense if it had counted less than 3000 and if so it
would shut the machine down and the encoder disc looked like a CD that was
glass with fine lines in it.. the sensor works on a laser and light
receiver it’s optical.. the ones I worked on had to be cleaned
meticulously with pure alcohol
Later or more common ones are now better sealed and common for things
like backguages that move and CNC machine parts

This one in the car has some magnetism on its tip. Maybecits got a reed
switch inside..

I’ve had reed switches apart and they are like a contact with a magnet that
gets moved and makes contact and breaks contact. It’s quite small, and
sealed up in a vacuum tube like a light bulb. they are reliable because
the contacts don’t spark since they have no oxygen..

With the encoder and modern technology the computer does count the pulses
around the circle and it also uses the zero position line. In the case if
the Volvo the zero position line is the place with no holes for an inch or
so..
I suspect the Volvo also counts the holes it’s perhaps roughly 50 per
revolution and read by the TDC sensor.

I have an old encoder that I salvaged from a machine and I wondered if it
could be run off the crank at the front but I realized I’d be dealing with
trying to meld the two types of sensors and a different number of pulses.
maybe that’s possible if you are really smart but it would of course be
totally impractical for me.

What you said about it completing one revolution reading the wrong number
of pulses and giving up then unlatching and no longer trying to supply
spark or fuel injector pulses is I think what is happening
The codes should verify it and I need to get a bit of time to wrap my head
around getting the codes and checking the orange wire

The test lamp I had I just hooked across the coil it “fires” when I get
spark and it fires for only about 1 revolution I can see it on when it
fires

If the key is turned back to start, but not to off then I won’t see a glow
or hear any firing on any more attempts at starting

If I turn the key to off then it will light my lamp and it will fire for
that first revolution once again..

I don’t expect it will be different if I use the orange wire rather than
the coil wires but maybe that confirms that the fuel injection is also
reacting the same way

Phil






















I stuck 2 screwdrivers in between against the case so as not to