[nathansonic18]

Hi everyone! Had my Formula 3 running pretty good while ago, but a couple of days ago, it wouldn't start. Checked the sparkplugs and they seemed to have spark and it popped like it was trying but didn't start.

So I figured I'd take a look at the CDI box. When I got it out, it didn't look like any wires were damaged.

So I wanted to ask if there was any way to test the CDI box or the stator


Any ideas on what's going on would be appreciated, thanks!

 

[TheBearAk]

I'm confused. In your subject line you said you have no spark and then in the text you say you do??

No real way to test CDI. You can test the stator using an ohm meter.

 

[nathansonic18]

I'm confused. In your subject line you said you have no spark and then in the text you say you do??

No real way to test CDI. You can test the stator using an ohm meter.

Sorry, I should've said there was very very faint spark at first, like i could hardly see it. Now there's no spark at all.

 

[TheBearAk]

I think I'd test the voltage at the stator, should put out between 30 and 45 volts AC. Then test the voltage coming out of the CDI, should be about the same 30-45 volts AC. Then test the voltage at the spark plug cap. Should be around 20,000 to 35,000 volts.

To test. Just put the test leads on the wires and pull the recoil a few times while watching the voltage. note the highest voltage.

But if that scares ya, then just taking an ohm meter to the stator and the coil might give some clues.

 

[nathansonic18]

I think I'd test the voltage at the stator, should put out between 30 and 45 volts AC. Then test the voltage coming out of the CDI, should be about the same 30-45 volts AC. Then test the voltage at the spark plug cap. Should be around 20,000 to 35,000 volts.

To test. Just put the test leads on the wires and pull the recoil a few times while watching the voltage. note the highest voltage.

But if that scares ya, then just taking an ohm meter to the stator and the coil might give some clues.

Alright, thanks. I'll give it a try.

 

[nathansonic18]

So I tested the stator and the highest voltage I got was 64 volts. I tested for voltage from the CDI box to the ignition coils, and I didn't get any voltage.

 

[TheBearAk]

Sounds like a bad CDI, but check connections, specifically the trigger coil

 

[nathansonic18]

Ok, and do I have to reprogram the dess? I've heard that it needs to be reprogramed if you replace the CDI box, otherwise it won't go above 2500 rpms.

 

[nathansonic18]

Also, I remembered that this happened before, but after I let it sit for a while the spark came back

 

[TheBearAk]

It has a DESS? Interesting. That is another can-o-worms. As the CDI is actually an MPEM

 

[nathanshadow18]

I got a new CDI box, and the first couple times I pulled it, I didn’t get any spark. But after a while, I got a little spark for a couple pulls then it would go away