Another 740T problem, Arg

After years of faithful service my '87 740T has left me stranded for the
first time, thankfully only a mile from my house so I was able to walk
home. I was driving through a parking lot and the tachometer needle
suddenly wigged out and was flipping all over the place for a moment
then the engine simply shut off. Now it turns over fine but doesn't even
try to start. I can hear the fuel pump running for a fraction of a
second after I stop cranking but the tach needle now just sits at zero
and doesn't budge. My first guess is the hall effect sensor in the
distributor but before I spend $50 on a new one I'd like some confirmation.

Also does anyone have experience with the aftermarket hall sensors FCP
Groton sells? The OEM Bosch sensor is nearly twice the cost.

 

I'd o some more testing first, but that's exactly the way the '87 EZK
control units would fail back in '87. They had a very high failure rate
for a few production weeks. If you drop the box down from its bracket by
the steering column and tap the tic-tac-toe pattern on the case in the
center square with the plastic end of a #2 Phillips screw driver while
an assistant cranks the motor and watches the tach you may see the
needle jump erratically to confirm a bad joint/component that lives
right in the center of the PCB for the EZK box.

Bob

 

Thanks for the suggestion, I actually have a spare ignition box
somewhere, I should drag that out and plug it in. That would rock if it
were just a solder joint, I can fix that easily enough. Is there any
good way to test the hall sensor? I don't know what the pinout is.