82c54 based computer "tachometer"

[Jonathan R. Lusky]

sdbartho at cca.rockwell.com writes:
>A few weeks ago,the local public access channel had a "learn-at-home" mechanics
> course that was being broadcast from a couple of tech schools down south.
> Anyway,they were working on the crank sensor on a 3.8buick when they went into
> a discussion on this very subject. Seems a lot of servicemen were forgetting
> to put the shielding back on the crank/cam sense wires, and it was causing
> random intermittent problems. The instructor then fired the car up without the
> shielding, and showed the crank waveform on the scope. Full of spikes! The 
> engine was also running like crap. Shield back on, everything was fine. A lot
> of the problems had to do with proximity to the coil packs. 

I got hit by the same thing in a Formula-SAE car last year.  We were
using a crank sensor from a quad-4.  Engine ran great on the dyno, 
dropped it in the car and it would only run intermittantly...
itermitant spark.  Checked all of our wiring, ran new wires to the MSD
just in case, still intermittant.  Checked the output of the crank
pickup with a scope, and it wasn't really pretty, but we had no idea
what it should look like.  Decided to check another crank sensor, and in
the process of removing it we had to pull the coil which was mounted to
the side of the car directly above the sensor.  Left the coil out while
we cranked, and bingo: beuatiful wave on the scope--so we figured it
must have been a bad sensor :).  Finally realized the problem when the
car went back to its old tricks after putting the engine back together
(and after sending our ECU back to the manufacturer to have them test it
and spending 4 hours bench abusing (testing) our MSD).


-- 
Jonathan R. Lusky  --  lusky at knuth.mtsu.edu
 "Turbos are nice but I'd rather be blown!"
   89 Jeep Wrangler - 258 / For Sale: $8000 obo
       80 Toyota Celica - 20R / 5spd