Ignition problem

[ozzie46]

Built Steve Hucks Lil Demon and am having issues with the hall effect sensor being ruined. I use a 12v batt and a dsage ectronic setup that I use on my 4 cyl. it works fine on the 4 cyl, but fries hall sensors on the Demon distributor. Could the small size of the Demon dizzy cause issues when using 12v?
the 4 cyl dizzy is almost 2in dia. the demon dizzy aprox 1in dia.
I got hall sensors From Roy Sholl.

Ron

 

[tornitore45]

Usually that happen when there is a piece of common GND between the spark loop and the Hall Sensor loop.
The GND to the Sensor should go to the Circuit Board GND pin and the chassis GND go back to the Circuit Board near the coil. None of the ignition current spike should run through the control circuit common called GND.
Anyway it help to have a small surface mount ceramic cap right on the sensor pins.

As a power supply designer I am an expert at keeping power current out of sensitive control circuit and yet I manage to destroy several sensors because..... I reversed the leads to the plug. I was grounding the tip and sparking the chassis. Did not realize the error until accidentally felt the chassis tingle.

 

[ozzie46]

Thanks Mauro, I'm confused because I have everything hooked up to the power supply box the same as for the 4 cyl engine and 4 cyl works fine and has done so for several years.
Although I do get a tingle if I touch the Demon V8 dizzy. Then the sensor fries, it seems, at that point.

An AHHA moment! It happens when I am trying to start the engine with a drill and I try moving the dizzy to find the sweet spot of timing. One hand on drill the other on the dizzy, could I be the ground frying the dizzy?

Ron

 

[tornitore45]

Diagnosing this kind of problem long distance is next to impossible. A good topological accurate schematic may help. By topological I mean that the connection sequence of components on the GND net truly represent the order an location of how it comes together.
Never heard the term "dizzy" but assume is the advance control lever.

Speculating. The drill should be double insulated unless you have a metal drill and driving the engine with a conductive connection. Basically your body offers an alternate path from chassis GND (the drill) and a metal point near the sensor. If any point of the sensor 3 wires harness has poor insulation to the chassis some current can jump from the "dizzy" to the harness and zap the sensor. Make sure the sensor and wires are covered with shrink tube and the GND wire in the harness goes back to ignition board, NOT to some metal GND.

 

[Tim Wescott]

As a power supply designer I am an expert at keeping power current out of sensitive control circuit and yet I manage to destroy several sensors because..... I reversed the leads to the plug. I was grounding the tip and sparking the chassis. Did not realize the error until accidentally felt the chassis tingle.

Oh, and you never smoke circuits at work through some dumb thumb error? You're better than me, then.

 

[tornitore45]

Tim, I never claimed to be immune from errors.
If you read and understood the post you quoted is clear that I affirmed the opposite.
I made many many dumb errors, too many to count or recall, some were pyrotechnically entertaining too.
I also made educational error from which one can learn a valid lesson if he is sufficiently humble and open minded to learn. Those type of error I do remember a few.

 

[mayhugh1]

An AHHA moment! It happens when I am trying to start the engine with a drill and I try moving the dizzy to find the sweet spot of timing. One hand on drill the other on the dizzy, could I be the ground frying the dizzy?

Ron,
Maybe what's happening is that you're rotating the distributor to a position where the spark isn't able to jump the extended tower gap plus the plug gap to reach ground. It's looking for any path and finds your hand, but when you pull away it then finds a path back through the ignition circuitry and eventually through the the Hall device. The solution might be to limit how far you rotate the distributor with either self or mechanical control or/and reduce the gap to the tower electrode with wider tower or rotor electrodes. - Terry

 

[ozzie46]

Thanks Mauro, dizzy = distributor, sorry.

Thanks Mayhugh1, that's something I will look into.

Ron

 

[cwelkie]

FWIW I'll second Terry's (Mayhugh1) suggestion. I managed to destroy 3 Hall Effect sensors before I realized that the mechanical advance was rotating the distributor body on my Cirrus "out of range" of the rotor/spark plug "post". Once I minimized the rotor to post gap and reset the rotational position of the rotor, all is well.
Charlie

 

[ozzie46]

Turns out the engine is pumping oil up the cyls. I used viton O-rings instead of cast iron. Never had an issue on my other engines that use them. I may have to remake cyl liners, so ignition is on hold for awhile.

Ron