[BUFFDRIVER]

I can't make this crap up. So after my 4 month ordeal with my 6 speed trans I finally get it out for a cruise with my daughter and I broke down. The distributor cap broke (torque made it hit the firewall) and tore the rotor all to hell. Fine, I throw another one on and make my way home and it starts to run like crap. I pull over, mess with the cap, get it to start again and make it home. I go to start it and nothing. Long story short after replacing the cap, rotor, coil, module, and a whole new distributor I got nothing. Finally trouble shoot it to the factory tach wire going to the cap. Ohmed it out and it reads 0.3. Is this normal? If I hook it up the car won't start. Why will the tach wire shut the car off if it's grounded? Did I fry my tach? How do I test it? I did install a DIY tach filter and everything did work for over 100 miles. This car is going to give me an ulser.

[Everett#2390]

I would suspect the filter 'bit the dirt'. The filter blocks the DC voltage but passes the AC component, the tach pulses, to the tach input coil and you are reading the primary winding of the coil circuit.
Time for an aftermarket tach.........

[Eric Kammerer]

Yup. When I was trying to troubleshoot if my OE tach was completely dead or just needed a signal filter, I made an adjustable one as described in the thread, to make sure I made one with the right components. When I turned the knob trying to find the setting needed to make the tach move, I found I could shut off the engine with the knob. So I gave up on the filter idea and set the tach out for rebuild (which it needed anyway, because it was completely dead). But I had never experienced such a small circuit killing the whole ignition like that.

[BUFFDRIVER]

I'm wondering if when the rotor let go the metal could have shorted something out under the cap.

[BUFFDRIVER]

GOOD NEWS! It was the filter. The tach works fine without it.

[go2fast]

We used to use the tach line for kill switches at the Chevy dealer I worked at many years ago.

[Steptoe]

We used to use the tach line for kill switches at the Chevy dealer I worked at many years ago.

That is a bit of useful information....
Thoughts on that Everett any issues that could arise?

[Steiner]

Probably isn't an issue unless ignition power is left on for awhile with the kill switch engaged. Otherwise it's like leaving the key on in a points system with the points closed although the points will about always give it up first.

[Everett#2390]

As Steiner suggested, not an issue, if used momentarily.
If ign switch left on and wire still grounded, contacts on point set will 'weld' themselves together.

[Steptoe]

With GM HEI not sure if u guys know this but leave the key on and the module switches off by itself...u cant burn out the coil etc.
And from above...dont understand this

The distributor cap broke (torque made it hit the firewall) and tore the rotor all to hell.

How can a dizzy hit the firewall when engine movement is lateral???
Even ripping apart a engine mount and having a wide cap GM HEI it cant hit the firewall.

[Steiner]

Yes, that's what a I was referring to and just comparing it to leaving points system turned on. Kill switch should only be an issue on a points system with key left on since it would power the coil to ground. No issue with the points themselves unless they were also closed and still probably not an issue as the kill switch would be parallel with the points and most likely be best path to ground.

With an HEI you'd still have the issue of coil heating up after awhile if using a simple kill switch because you'd still be powering the coil with a ground connected to the negative terminal which is not the same state as when just the key is turned on.

Bottom line is that it's not good for any dc coil to be left with power on the positive and straight ground on the negative for a long time. I reckon you could add an rc circuit or just a resistor to it to protect the coil like the condensor but for a simple kill switch there's no reason to since who leaves their key on and then just walks away from the car? OK, me when I used to listen to the radio in my dad's truck but that's about it.

[go2fast]

Originally Posted by Everett#2390

As Steiner suggested, not an issue, if used momentarily.
If ign switch left on and wire still grounded, contacts on point set will 'weld' themselves together.

I'm sorry, but this makes no sense. The points ground the coil. So putting a switch on the negative of the coil (to ground) bypasses the points entirely. The coil and resistor wire will draw a little current, but that's about it. Besides, I thought we were talking about an HEI?

[Steiner]

Originally Posted by go2fast

I'm sorry, but this makes no sense. The points ground the coil. So putting a switch on the negative of the coil (to ground) bypasses the points entirely. The coil and resistor wire will draw a little current, but that's about it. Besides, I thought we were talking about an HEI?

You're right. See above. I just mentioned the points as a comparison to what it's like just grounding the igition system...as in you can damage something if left for awhile. I think Everett was just making a quick response that came out wrong.

[Everett#2390]

Steiner's right, I reread this AM, and it doesn't read correctly.
I honestly don't know what I was thinking................