Tach Kills Engine, When Tach is connected to coil, engine quites after running for 4 minutes? Options

[struckn]

This has me really confussed. I have Pertronixs in the dizzy and a MSD Blaster 2 Coil, Carb conversion from FI, '74 four. It runs great as long as the tach is disconnected at the coil. If I plug the tach into the negative coil terminal the engine will start, run normally and the tach works perfect at all RPM's. But after running only a few minutes the engine shuts down and will not restart unless I disconnect the tach wire from the coil. Any suggestions would be really appreciated, thanks.

Doug

[underthetire]

Do you have the ballast resistor on the msd coil?

[struckn]

Do you have the ballast resistor on the msd coil?

No, doesn't have a Ballast Resister, fed from a Pertronix in the Distributor.

[underthetire]

Better double check then, the pertronics units I think need it to keep from overheating. The stock coils have it built in. Should be something on their website to measure the coil resistance to determin if it's needed or not.

[struckn]

Better double check then, the pertronics units I think need it to keep from overheating. The stock coils have it built in. Should be something on their website to measure the coil resistance to determin if it's needed or not.

Thanks,
I Ordered from Advance Auto a MSD .08 ohm Ballast Resistor. Should pick it up Tuesday and give it a try weather permitting. The MDS Blaster 2 Coil does not have an internal Ballast. It was on the car when I got it along with a MDS 5 Box and the Pertronix under the Dizzy Cap. So, According to what I've research the Ballast resistor isn't require if using the MSD 5 Unit, but I've disconnected the MSD 5 Unit and beleive it's defective.

Car runs better with just the Pertronixs and the MSD Blaster Coil.

I check the Pertronics instructions and it say if the coil is 1.5 Ohm use the resistor for normal applications, but not for racing. If the coil is 3.0 Ohms for normal applications remove the resistor. The MSD 2 Blaster coil is less then 1.5 Ohms so it won't hurt to try installing the Ballast Resistor to see if the engine runs OK,

Then when ready I'll plug the tach back in to coil negative pole and see what happens.

[underthetire]

You can get them at radio shack btw, just a ceramic resistor. May or may not be whats causing the tach problem, but worth a shot. My thinking was the tach was putting just enough extra draw on the pertronics, causing it to overheat. I may be way off base though. Could simply be the tach or wire shorting out.

[struckn]

You can get them at radio shack btw, just a ceramic resistor. May or may not be whats causing the tach problem, but worth a shot. My thinking was the tach was putting just enough extra draw on the pertronics, causing it to overheat. I may be way off base though. Could simply be the tach or wire shorting out.

I was thinking the draw from the tech might have alot to do with it too, or some how was breaking the signal from the Pertronix to the coil. Don't think I've hurt the Pertronics yet.

I keep reminding myself problems like this are part of the fun in this Hobby. Old cars are supposed to need fixing and figuring out the puzzles they throw at us makes it interesting to say the least. I also have a "68 AMX and a '69 C1O Pickup. Went threw this sort of thing with both and got them to the point that there's really not much more to do to them other then wax drive show maintain. I'm really happy with the 914. The 914's were always high on my Bucket List and finally got a nice one to make into a great one in time.

[struckn]

Problem solved! Talked to Pertronix Tech and bought a 3 OHM Pertronix Flame Trower Coil. Installed and everything including the Tach is working perfically. The MSD 5 is removed and the 1.4 OHM MSD Blaster 2 Coil is replaced.