‘85 250sx no spark

[lndy650]

Yup measure using ground.

[MikeD70]

I went down to my shed and looked in my notes this is what i have for testing the wires at the 6 pin connector off the CDI see if this helps at all.
Blue/Yellow- pulse generator= 290 to 360 ohms
green/red- neutral switch off= 2 ohms on= infinity
black/white- kill and key switch off= 2 ohms on= infinity
green- ground= .1 ohms
black/yellow- ign. coil= .3 ohms
black/red- ac voltage= 250-400 ohms


edit: forgot you have a manual so you probly have all that info... try unplugging the kill switch to rule out a bad switch

Black/yellow - 329.3
Green/red - 3.5 in neutral, Meg ohms in gear
Black/white - ok
Green - .3 to frame
Black/yellow - .4
Black/red - 315.7


Thanks for all your suggestions.

[lndy650]

i would check make sure your ground wires are connected to the frame and aren't broken anywhere. Its probably the coil you can get them pretty cheap on ebay. Wish i could help you in person i hate trying to help fix things over the internet.
https://www.ebay.com/itm/IGNITION-CO...tZwWUZ&vxp=mtr

[Rob Canadian]

Have you tried a new plug? Seems simple but never saw it posted up.

Did you disconnect the kill switch? I see you tested it. Contacts are always one of the first places to check. What looks good on a DVOM may not work well under load.

Also give the CDI a couple taps with a screwdriver. Yes they are solid state. (No moving parts) But heard it works.

[MikeD70]

i would check make sure your ground wires are connected to the frame and aren't broken anywhere. Its probably the coil you can get them pretty cheap on ebay. Wish i could help you in person i hate trying to help fix things over the internet.
https://www.ebay.com/itm/IGNITION-CO...tZwWUZ&vxp=mtr

I will check the grounds. Will most likely get a coil and try that. Thanks for the link for the coil.

[MikeD70]

Have you tried a new plug? Seems simple but never saw it posted up.

Did you disconnect the kill switch? I see you tested it. Contacts are always one of the first places to check. What looks good on a DVOM may not work well under load.

Also give the CDI a couple taps with a screwdriver. Yes they are solid state. (No moving parts) But heard it works.

Ues, disconnected the kill switch, no continuity between the green and black/white wires.
Tried a spare plug, but not a brand new one. Going to get a new one and try it.

[MikeD70]

Tried new plug , no spark.
Got new ignition coil and tried that, still no spark.
Is there any way to check/test the CDI unit?

[lndy650]

damn shes a tricky one. As far as i know theres no accurate way to test a cdi the only sure way is rule out everything else or replace it. i still think because when you tested the coil from the cdi plug it was out of spec that theres a small possibility there could be a pinched or damaged wire.
you said you tested the exciter coil right? one other thing is the pulse generator gap. to test this without pulling the side cover set your volt meter at the 2 volts setting (or the closest to that because the pulse gen only puts out around 1 volt) test between the 2 wires from the pulse gen and crank the engine. you should see a voltage fluctuation of around 1 volt.
if all of this checks out and you buy a cdi you should be able to find a cheap one on ebay but i would recommend an original i know its taking a chance on a used one but im skeptical of the aftermarket ones on there. maybe someone here has tried them and can vouch for them.

[MikeD70]

damn shes a tricky one. As far as i know theres no accurate way to test a cdi the only sure way is rule out everything else or replace it. i still think because when you tested the coil from the cdi plug it was out of spec that theres a small possibility there could be a pinched or damaged wire.
you said you tested the exciter coil right? one other thing is the pulse generator gap. to test this without pulling the side cover set your volt meter at the 2 volts setting (or the closest to that because the pulse gen only puts out around 1 volt) test between the 2 wires from the pulse gen and crank the engine. you should see a voltage fluctuation of around 1 volt.
if all of this checks out and you buy a cdi you should be able to find a cheap one on ebay but i would recommend an original i know its taking a chance on a used one but im skeptical of the aftermarket ones on there. maybe someone here has tried them and can vouch for them.

Checked resistance of exciter at CDI plug. It measured in the standard according to the service manual.
I will check the voltage measurement of the pulse generator.
Is it possible to check voltage at the ignition coil?

[gimmeamidget]

Can you check the wire going to the coil to see if there is pulsed voltage going to the coil. I use a tester light but voltmeter should show some level of volts on the wire feeding the coil. I suspect there is no voltage going to the coil to make the spark.

[gimmeamidget]

Just hook tester to the wire and crank over and see if light lights up.

[MikeD70]

Can you check the wire going to the coil to see if there is pulsed voltage going to the coil. I use a tester light but voltmeter should show some level of volts on the wire feeding the coil. I suspect there is no voltage going to the coil to make the spark.

There are 2 wires going to the ignition coil, check voltage across these 2 wire?

[gimmeamidget]

One should be ground and the other volts so yes you can measure voltage across them while turning over bike.

[lndy650]

if you bought a new coil and you still dont have spark then theres not going to be any voltage going to the coil. this is why if the exciter coil is good i think you should test the pulse generator. if the pulse gen checks out the cdi or a broken/grounded wire is about the only thing left to rule out.
what was the reading on the exciter coil?

if the exciter is good then you have voltage going into the cdi. the only possibility now is why the cdi isnt passing the voltage along to the coil.theres 2 likely causes. 1, either there is a kill wire grounding or a bad kill switch(which is why we unplugged the kill switch to rule it out) or 2, the pulse gen isnt sending the message to the cdi.

Now as for ruling out the kill switch and the key im not there in person so i cant say for sure but the wire coming off the cdi splits and goes to the kill switch and the key on/off you should be able to disconnect the wire from the cdi where it splits into two. its open circuit which means if the circuit isnt grounded it will run so if its unplugged you rule out the possibility of an issue past where you unplugged it.

let us know the exciter coil ohms and if the pulse gen is sending a pulse and we will go from there. im saying to use an ohm meter on the lowest setting because i dont think the voltage from a pulse gen will light up a test light(it may but 1-2 volts might not be enough and youll see the change on an actual meter while cranking)

[lndy650]

i scanned the page of my manual for the exciter coil test its probably the same as the online manual i just wanna make sure