‘85 250sx no spark

[MikeD70]

85 250sx not getting any spark at the plug. Downloaded the service manual and started doing ignition system checks.
Checked various continuity readings (ignition and run switch) between black/white and green wires at CDI plug, all checked good.
Measured resistance between (ignition coil) black/yellow and green wire at CDI plug, 0.4 ohms (standard ie 0.1-0.3). As suggested in manual, check resistance at coil terminals, measured 0.3 ohms (standard is 0.1-0.3)

Any ideas if it is normal to measure outside the acceptable range at the CDI plug , but measure inside the acceptable range when reading across the coil?
Since the value is at the upper range, should the coil be replaced?

Also checked measurements for alternator and pulse generator at CDI plug and measurements were all within range.

TIA for your input.

[gimmeamidget]

Pull the rubber boot off the wires on the back of the key switch and check the connections. I have seen a few where the solder fails and power is not routed through switch.

[lndy650]

am i right that what you are sayin is when you test the coil from the wires it reads .4 and unplugged it reads .3? if so what is your secondary coil resistance? it should say in the manual what it should be probably like 7.5-11k through the plug cap and 3.5-4.5 with the cap removed. those are general numbers check your manual for exact numbers. the secondary reading should be between the green wire and the spark plug wire with and without the cap

[lndy650]

Its rare but i have had no spark be as simple as a bad plug cap or wire.

[MikeD70]

Pull the rubber boot off the wires on the back of the key switch and check the connections. I have seen a few where the solder fails and power is not routed through switch.

I checked the switch, checked out ok.

[MikeD70]

am i right that what you are sayin is when you test the coil from the wires it reads .4 and unplugged it reads .3? if so what is your secondary coil resistance? it should say in the manual what it should be probably like 7.5-11k through the plug cap and 3.5-4.5 with the cap removed. those are general numbers check your manual for exact numbers. the secondary reading should be between the green wire and the spark plug wire with and without the cap


Correct, .4 measured at CDI plug, with wires connected to coil, .3 measured across the coil.
Measured the secondary, 24.7k with the spark plug cap, 4.0k with cap removed.

[MikeD70]

Its rare but i have had no spark be as simple as a bad plug cap or wire.

Any idea how to check if the plug cap is bad?

[lndy650]

testing with a lead on each side of the cap it should be around 5k ohms

[lndy650]

24.7k with the cap is really high

[MikeD70]

24.7k with the cap is really high

Measured just the spark plug cap and go a reading of 22k.

[lndy650]

Yup I would try a new cap. not gonna say thats it for sure but its very likely thats way high for a cap

[MikeD70]

Yup I would try a new cap. not gonna say thats it for sure but its very likely thats way high for a cap

Checked the cap on my 85 200x it measured 5.2k. Put it on the sx, still no spark.

[lndy650]

hmmm... my next guess would be the coil. its hard diagnosing something over the internet. ok so first check your green wire that goes between the cdi and coil and check where its grounded to the chassis. Next the black and white wire that runs from the cdi to your ignition key and kill switch is your kill wire if it contacts any part of the chassis you will lose spark make sure its not grounding out anywhere.

edit: Stupid question but your neutral light is coming on right?

[lndy650]

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

[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

My neutral light is on.
I do have a manual I downloaded from a link on this site.
However, I will check the points you mentioned.
Measure each pin to ground I’m guessing??

[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-COIL-FITS-HONDA-ATC250ES-ATC250R-ATC250SX-1985-1986-1987/281241788650?fits=Make%3AHonda&hash=item417b5120ea:g:s78AAOSwEotZwWUZ&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-COIL-FITS-HONDA-ATC250ES-ATC250R-ATC250SX-1985-1986-1987/281241788650?fits=Make%3AHonda&hash=item417b5120ea:g:s78AAOSwEotZwWUZ&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 sure249020

[MikeD70]

https://youtu.be/LUftRXfItHk

Video of meter connected to ignition coil wires while cranking.

[gimmeamidget]

That doesn't appear correct. I have only used a tester light but the light was lit the whole time but fluctuating between dim and bright. I would have expected to see the meter hover between low volts and 12v. It appeared you may have had 12v but very seldom.

[gimmeamidget]

Kind of looks like symptoms from a bad ground or could be bad cdi. I would double check all grounds and make sure connectors are good and ground ohms out at 0. Do you know anyone with same bike you could swap cdi with?

[Doug8765]

I think the crankshaft that runs the stator breaks by the stator it happens


Sent from my iPhone using Tapatalk Pro

[MikeD70]

https://youtu.be/3YDjyYc2ZKk
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)

Exciter coil ohms measured 317.3
Pulse generator ohms measured 330.9
Haven’t checked voltage on the pulse generator yet, will check as soon as I get a chance.

[MikeD70]

Kind of looks like symptoms from a bad ground or could be bad cdi. I would double check all grounds and make sure connectors are good and ground ohms out at 0. Do you know anyone with same bike you could swap cdi with?

Ill check all the grounds again. I only found grounds at the frame from the battery, a ground on the rear frame near the tool box (green wire) and where the starter grounds.

Unfortunately I don’t know anyone with the same bike to swap the CDI.

[gimmeamidget]

If you can pm me your name and address I can pull my Cdi off my 85 250sx....it's the single connector not the double connector type....and send it to ya to try if you could send it back after you try it. That way your not throwing money at it not knowing if that's the problem.

[MikeD70]

https://youtu.be/3YDjyYc2ZKk

Video of meter reading on pulse generator blue/yellow wire and green/white wire.

[MikeD70]

That would be awesome. I’ll pm you.

[lndy650]

ya looks like its gotta be the cdi the pulse gen is definitely good

[MikeD70]

I'm just wondering, the values given for the resistance measurement give one for ND and one for MITUBA (have no idea what this stands for), which value should I be comparing to?

[MikeD70]

I'm just wondering, the values given for the resistance measurement give one for ND and one for MITUBA (have no idea what this stands for), which value should I be comparing to?


UPDATE: I swapped out the CDI with one from another running bike, still no spark! :wondering:confused:

[lndy650]

ok so the exciter coil tested good, the pulse coil tested good, good wire and cap, new coil, and cdi off running 250sx. im thinking it has to be a bad wire somewhere. with this new coil what is the coil reading from the cdi plug is it still over spec at .4 or is it in spec now?

[MikeD70]

ok so the exciter coil tested good, the pulse coil tested good, good wire and cap, new coil, and cdi off running 250sx. im thinking it has to be a bad wire somewhere. with this new coil what is the coil reading from the cdi plug is it still over spec at .4 or is it in spec now?

I will have to double check the reading on the new coil. I got it on eBay, but it is an aftermarket one.

[lndy650]

i was thinkin it might be possible theres bad wiring if the reading is still high at the cdi plug but normal at the coil

[MikeD70]

i was thinkin it might be possible theres bad wiring if the reading is still high at the cdi plug but normal at the coil

New coil measured .06 at CDI plug, not sure if this should be in spec since it is an aftermarket coil and not an oem one.
Is it possible the exciter is not putting out correctly even though the resistance measured in spec. Can the voltage out be measured for the exciter, if so what value should I expect?

[lndy650]

im not sure how much voltage the exciter coil would produce at the rpms of the engine being cranked over but at high rpm i think its somewhere around 100.
ok so the exciter puts out ac voltage to the cdi so technically you could test for any ac voltage coming out of the exciter. if you get a reading then test the wire that sends that voltage to the coil and if theres no reading you know its the cdi and if there is then its the coil. anyway seeing the cdi is off a running bike we know that should be good.
I did have this arctic cat f1000 once that had a bad computer but replacing it resulted in a second of spark then nothing. turns out even though the ohms reading was ok the exciter coil was producing too much voltage and burned out the computer. i ended up having to buy another computer and a new stator which together at our dealer cost was almost a g note.

ill look more into the rated output of the exciter coil and you test it at crank rpm with your meter on ac volts and see what you come up with.
as far as the coil reading your right .06 might be ok for that coil. is the reading at the coil .06?

[gimmeamidget]

He posted a youtube video of him testing at the coil in AC volts and it appeared the voltage was only there part of the time but I am wondering if the meter cant read fast enough to keep up with the on/off volts. I always just used a cheap tester light and it flashed as I would expect a spark at the plug. I did see volts which I think should have been amped up at the coil and produce a spark....maybe not correct but some sort of spark.

[gimmeamidget]

I would try pulling off the cap on the OEM coil and cutting 1/4" off the wire and replacing the cap to ensure a good connection and rechecking resistance. I like OEM to cheap stuff.

[lndy650]

yes the video he did was the external coil and you wouldnt have constant voltage you would only have voltage when the cdi tells it to send a spark so ya its gonna look screwy on a meter especially set to auto-range. the test light is worth trying if he has one.(if not they are a couple bucks) Im pretty sure i already had him test the plug wire on the old coil and it was good but that is a good idea to cut the wire back a little and your idea to use the old coil now that he has a cdi from a running atc is also a good idea couldn't hurt to try.
im asking him to test the voltage out of the exciter coil(internal stator coil) because i think we should try starting from the source of the ignition and work our way up.