MSD analog relibility; any ideas?????

Bill Dedman said

My tach is an el-cheapo Summit unit that uses the signal that is picked up on the negative side of the coil.

The "techs" at MSD told me that this 5462 sends 100+ volts to that "minus" coil terminal. I know I heard them right... two of them told me that; something about minimizing "rise time" in the coil.

That doesn't concern me.

This tach has always worked well.

I'm wondering whether the 100+ volts might have a shock for it that it won't survive... so, I haven't hooked it up... yet.

Do you have any thoughts on that?

If you do, I'd appreciate your opinion.

Click to expand...

Bill,

Another MSD support tech smoking Crack!

Notice the instructions tell you to get power for the BTM from the + side of the coil ?

If the unit was outputting 100+ volts it would be fed back into the rest of the cars electrical system and burn out the car's electrical system. It's only the capacitive discharge systems (6A, 7A, etc) that use a high voltage output into the coil to cause a spark on the rising edge of the pulse.

Based on the way the unit is connected it is operating as an inductive system just like the mopar ecu. Current is flowing through the coil out the orange wire of the BTM to ground through the BTM. The BTM will disrupt the current flow by opening the ground path causing the magnetic filed in the coil to collapse inducing a potential on the secondary windings of the coil.

The circuitry in the BTM is looking at the rate at which it receives pulses from the magnetic pick up and will adjust the point it opens the ground path to cause the timing to be retarded.

FWIW, I was having trouble getting the 6A unit I have to trigger directly off the magnetic pick-up. A couple of calls to the MSD tech line was of no help but; I did sign up for there message board and there was lots of useful help there including a MSD tech that does know his stuff.