Testing ford duraspark dizzys...

[wayne petty]

a bit of theory and hands on this time....

ford duraspark dizzys have been used starting about 1975 through 84-85 or so... with remote mounted modules...

there are 3 wires coming out....    

black ....    this is ground for the ign module..  and is connected to the breaker plate hold down screw that also holds down the grommet..

without this wire and the body of the dizzy properly grounded the ign module will not have any ground...   no ground ... no spark....

you can test these units with the dist removed... if you use a ground from the block to the housing...   spin the shaft... watch the coil arc....


the orange and purple wires are connected to the pick up coil windings...

use a digital ohm/volt meter on them.... set it to 2,000 ohms scale... usually shown as    2Kohm...   it should read 600 to 800 ohms...

while the meter is still connected... flip the knob over to 20 volt a/c scale...   spin the dizzy shaft..   with your hand you should be able to generate over 1 volt A/C  ,    if it does not generate this much signal voltage it will not turn on the power transistor in the module and charge the primary in the coil...      no charge/saturation    no discharge... no spark...

i had one in my hand today as i was installing a duraspark on the fairlane project...      it read 640 ohms...  but could only create 0.62 volts A/C...

this was a reman dizzy from the parts store....    i wanted to install a new reluctor but nobody has them local..  it was brand new anyway(reman)... so off to the store that had that one in stock...  took my meter... hooked it up the replacement... got almost 5 volts a/c out of it.... fired right up....    magic...

oh... and the reluctor....   it is a chunk of sintered material...

it retains a small amount of magnetic field for a short time...

if the reluctor has been washed.... dipped...  sandblasted... dropped... cracked...   it may not retain enough magnetic field to create proper signal voltage in the pickup coil....     no start...    everything checks out perfect..  still no start...     ford and dodge are victims of bad reluctors causing no starts... or extreamly hard to start cars....

gm on the small cap dizzys has a slightly differnt problem... the reluctor is stamped steel and riveted to the dizzy shaft...  there is a ceramic ring magnet in this riveted sandwich...   when the magnet cracks do to heat cycleing..   hammering... dropping of the unit...   it will create extra pulses out of phase that the ignition module does not know what to do with...  makes for a hard to find misfire....

[phat46]

I'll have to remember this, i have one of those on my truck. mine is fired by a chevy ign. module though. Apparently the Ford mod. was bad, I wired in the Chevy one and it fired right up!

[wayne petty]

when you said that... i just remembered...  i put a chevy module on a toyota truck when that module blew out...


i have also used them on ford apps...  only one thing... you have a 50-50 chance of getting the wiring from the pickup coil right...    if when installing one...  for everybody who reads this....     if the wires from the pickup coil are backward    it will fire the coil between the cap terminals...  out of phase...  runs really bad...   swap the wires before doing anything else...   in case it does not run well ....

[junkyardjeff]

My experiences with the duraspark ignitions are if it will start when cold and then shuts off when everything warms up its usually the module and then if it will not restart when hot and then will restart when the motor cools down its usually the pick up coil in the distributor.  Jeff

[wayne petty]

i post this to help people understand what the reluctor does in the igniton system...  the book shows  the resistance test... they do not show the a/c voltage output tests...    

without this tidbit of information...  one can chase his tail all day on a dead car....  

with it...  30 seconds after you do a resistance test on the pickup coil  and you know if the dizzy is good...

you can even test it at the module connector..

if you have resistance at the pick up coil connections...  just flip the range setting over to 20 volt a/c

[UGLY OLDS]

BOY.. :!:  That Wayne guy is a pretty smart feller ...Helpful too...

I had the reluctor "ceramic magnet issue" he described above on a Suburban..The truck ran great but would not idle..INTERESTING scope pattern..Showed multiple cylinder firings...NOBODY could explain it .... :oops:

Might be a good idea to copy & keep these posts in a "fix-it" file... I Am..

THANKS WAYNE  :!:  :!:  :b-d:

Keep 'em coming  :!:  );b(


Bob.....

[Crosley.In.AZ]

Wayne...... interesting stuff.

I finally  had time today , so I hooked up the v-ohm meter to the dizzy for my 200cid Ford motor.

easy spinning produced 1.3 to 2.0 volts on the meter.

thanks.

[Crosley.In.AZ]

I just did the same test on a HEI large cap dizzy... same results , about 2 volts on the ac setting.