TR6 distributor--ignition question

[charleyf]

I am writing for a friend who has a TR6. When he bought this car it had a NonTR distributor ( possibly a Jaguar)and there are no visible numbers on the distributor. The car has a MSD unit on it. Just recently he started having problems with the ignition that eventually resulted in a complete ignition failure. He bought a new MSD unit for it and the car runs fine with that. However, he was looking at a backup situation where he could run the car without the MSD. What we found was that the spark was very weak. Upon trying to start the car, we would get a couple of good sparks on a exposed plug and then the spark was very weak or none at all. The car would not run without the MSD unit hooked up even though everything was hooked up as per a normal points car.
Could there be something in that distributor that needs the added power of the MSD to be able to run the ignition system with enough power to fire the plugs? I should add that he put a new coil on during the process of trying to chase down the problem. The only other modification visible is an electronic tach because the distributor does not have a tach drive on it.
Charley

 

[NutmegCT]

Charley - try replacing the ignition condenser.

Tom

 

[charleyf]

The condenser was also changed during the fault finding process.
Charley

 

[TR3driver]

I'd be looking at how much juice actually gets to the coil with the points connected and closed. Also, check the spark right at the top of the coil, as well as the "end to end" resistance of each plug wire (from terminal inside the cap to terminal at the spark plug).

When I ran a MSD 6A on my TR3A, the higher spark current both burned up plugs quickly, and eventually burned out the resistor inside the distributor cap. It also would keep running even with a failed cap and wires (separate incidents), as long as the plugs were still the easiest path to ground. Obviously, the points are much more limited in output voltage, so the spark with points may not be able to jump some impediment that the spark with the MSD was jumping. With the MSD, the spark would literally jump from the center terminal to a side terminal on the coil, if it didn't find somewhere else first!

I also went to colder plugs with the MSD, and had to go back to hotter for points (and the Crane that replaced the failed MSD). Depending on how you are checking the spark, the cold plugs may have gotten glazed and be bleeding off spark voltage.

 

[trrdster2000]

Charley, try getting your spark from the positive terminal on the battery to you positive on the coil. You may have a ballast resistor that's putting out low voltage after starting cycle has been completed.

Wayne

 

[charleyf]

Thanks for the ideas. We will try these and see if we can figure out what is going on.
Charley