318 has no spark

ok its a 318 with electronic ign box. has been running fine. then going to work it started missing then back fired a couple times ran ruff then died. it stopped firing. ok i have replaced the pickup in dist,new coil, new ign box. the dist was only about a month old as well as the box, wires and plugs. but stuff goes out so i got new ones to make sure. im getting power on the pos and neg sides on the coil with the key on. i put a test light on the neg side and cranked over but no flashing happend like no turning of dist. but of course its turning. what should i check. i even grounded the ign box right on the intake to make sure good ground. should i have power on the neg side at all times? any please help  

when i had that problem it was an issue with the actual box not grounding.  the car would just shut off sometimes. sounds like you've covered all your bases.  lemme think on it.  

how the ignition box works...

it controls the NEGative side of the coil..    

when it sees the small AC signal from the pick up coil  go over 1/2 volt Positive.. the power transistor inside the module connects the negative side of the coil to ground..  this completes the circuit and creates a magnetic field in the primary windings in the coil..    when the AC signal from the pick up coil drops to 0.  the power transistor switches off and releases the ground connection to the negative side of the coil..    this causes the magnetic field to collapse through the secondary and create a high voltage spark..      the  ac signal from the pick up coil continues to 1/2 volt negative..  then swings to 1/2 volt positive again as the reluctor tips start to line up again. turns on the transistor .   as soon as they line up.. the voltage drops to 0 and the coil fires again..

testing the module..  take it off.. take it to a parts store.. they have an automatic tester for ignition modules..


testing on the car...    with a digital volt meter..  unplug the pick up coil...   set the digital volt meter to 2K ohms..    measure the resistance of the pick up coil   usually around 980 ohms.. but anywhere between 500 and 1500 is expected..
before disconnecting.. flip the meter settings to 2 volts AC or 20 volts AC..  crank the engine.. or spin the distributer shaft.. see if you get really close to 1.0 volts.. i like to see just over 1.0 volts AC voltage...

if the pick up coil resistance measures out ok...   but does not create 1.0 volts AC it won't trigger the ignition module to turn on the power transistor to charge the primary windings (complete the circuit to ground) so there will be NO spark .
the reluctor can fail..  


you can..  with the distributer out.. spin the shaft with the pick up coil connected.. and the ignition coil will spark if the system works..    

Are you running a stock mopar electronic ignition coil???

did you buy your module from a place that has a lifetime warrantee on it???   Hopefully...




 

Ok I figured it out. I just did not have time to come back and post. The coil shorted out and fried my ign module. And at first I just put the New box on it without changing the coil so it fried it and I did not know. So long story short I used the New coil and got another new box and it started. So note to self. If your box goes bad replace the coil and the box before u try anything else. Thanks guys  

i hope that you come back and read this..


if you burned out the coil...    and now replaced it and the module..


i would really LIKE you to measure the voltage on the POSITIVE side of the coil.. when you turn the key on... while cranking then back to run...

voltage at the positive side of the coil...   between the coil POS + and GROUND on the engine block...

key OFF... 0.00

key ON but the engine NOT running..   somewhere around 9 or 10 volts...

ENGINE CRANKING....     the coil should have close to battery voltage.. about 12.5 volts...

released from cranking and the engine running..   8 to 10 volts...  engine running...


if something is screwed up.. and you have a stock mopar ignition system.. and the voltage stays high all the time..   you will burn out your coil in a few weeks to a few months..   as these types of coil were NOT designed to work with full battery voltage on them for more than a minute while cranking..  they are JUST NOT DESIGNED For it..    the coil is actually designed for 9 or 10 volts..   it will work at 12.5 for a short while.. . it will burn out the primary windings at 14.1 ...


TEST TEST TEST>. or end up on a tow truck...  swapping the same parts again and again and again...   did you buy your car to constantly swap parts.. or to drive and enjoy it when you turn the key... ????

i wish the THEORY on how it actually is supposed to work was easier to access.. i seem to have it all stored in my head...  

Thank. Ya I came back and read it. I will check that tomorrow and see what I have after I replace my front axles in the truck. Note to self don't buy the cheap u joints from advance auto parts. Buy the good ones. I was in 4 low pulling another truck and the u joints broke in half destroying my axles.. luckly I ordered them through the commercial acc. At work and they will be buying me New axles. The u joints were only less than a month old and they broke like glass .  

a quiet secret...

there are places like PTO sales.. and some rear end shops.. that sell  spicer wheel joints..   wheel joints are like U joints but designed for front drive axles..   but your shafts will probably come with new joints installed..


i figure that you have a W250... here are some articles you might enjoy from the dozen or so truck magazines on this site..


http://www.dieselpowermag.com/sch/02/w250/articles/index.html?SearchSource=Group


enjoy...