MSD Adventures

For nearly 15 years my ’83 SC had been completely reliable.  It never let me down or left me doubting the wisdom of shunning membership in the AAA.  That is until a fine autumn afternoon when its Achilles heel became evident.

After a short blast up Route 8 I turned onto State Route 59 and headed towards Silver Lake.  At the first intersection I shoved in the clutch as I came to a full stop at a red light.  The engine promptly died without warning.  Repeated attempts to get it to fire were futile.  Plenty of cranking power was available from my battery, and the engine spun freely, but the engine would not come back to life.

With the aid of a friendly motorist I pushed the SC out of the intersection and into the parking lot of a conveniently located gas station (not one with any semblance of service, only fuel and Fritos).  A check in the engine compartment revealed nothing obvious or simple, so a call was placed to my original destination, friend Rick’s house.  After several well considered road-side attempts to diagnose the problem, and much head scratching, we gave up and winched it onto Rick’s Trailex.  It was the first trailer ride for the SC since its last track adventure many years ago.

The final diagnosis was failure of the CD Box; the Bosch device that was so high tech in the early 80’s and is now a curiosity of transistors and antique automotive electronics. 

The route to a conclusive diagnosis was rather long and involved, but could have been short and simple had I asked Jeff  “Sideways”  Bernstein who pointed out that if there is no whine from the CD ignition after you turn on the key, the box is a goner.  Instead my efforts to figure this out entailed a trip to Steinel’s to borrow a known good Bosch box that when temporarily installed let the SC run without complaint.  Culprit confirmed.

Anyone has gone down this road will tell you that the Bosch units are breathtakingly expensive to replace.  And the common cure is to install an MSD unit. I undertook this fix, a path made simpler by the fact that Rick had traveled it before.  I had the benefit of his wiring and mounting experience, invaluable to the amateur wrench turner.

Where our experiences diverged, nothing being simple in matters automotive, was with the adapter MSD sells for use with tachometers that do not care for the square sine wave that the MSD unit delivers for the tachometer  to interpret.  On Rick’s SC it has worked for along time without fail.  On my SC the tachometer worked for about 25 miles or so, then became erratic and finally died altogether.

A conversation with a technician at North Hollywood Speedometer, a well-known source for VDO gauge repair that I have used before, provided an answer to the mystery as to why Rick’s tach would work and mine would not.

The technician explained that the tach adapter is just a capacitor and that the quality of its signal can vary depending on the production run from which it comes.  MSD’s sources are apparently varied, or at least not consistent, so what works in one installation may not be duplicated in another.

 It may have also had something to do with the vintage of my tach, which was stamped with a 1979 build date, whereas the car was built in October of 1982.  In any event, NHS’s tech was not surprised that a seemingly identical installation in a vehicle of the same type and model yielded different results.

After a trip across the country courtesy of UPS and the installation of a new circuit board by the good folks at North Hollywood Speedometer, my tach arrived and was installed.

After a simple installation I took the SC out on the street to see how things worked.  They did, but only partially. An abrupt cut-out of the engine at 3500 RPM’s on this first test drive lead me to utter the common question of marginally talented mechanics:  “What the hell?”  

After another round of head scratching and the picking of Rick’s memory I found the source of what was to be the ‘last problem’ in this project.  The stock set up includes a rev limiter connected to the tach.  This must be disconnected (see your wiring diagram) and covered or taped, else the beast will think 3500 RPM’s is 6300 RPM’s and will try and throw you through the windshield when it abruptly cuts out as you accelerate with any enthusiasm. 

The MSD unit delivers a more consistent and better spark at high RPM’s than the old Bosch unit.  Coupled with the very cool “soft” rev limiter, which can be adjusted by installing different modules that dictate the RPM limit, it is a slick set up indeed.