johnflys1

My Feedback: (3)

My 3W 75 shut off in mid air. No spark to the plug. I sent the box back to Cactus and they say the box is good. They sent me a new shaft pick up and it still will not spark. The battery is hot and the switch has been by-passed. Have I missed anything? I still think the box is bad. Thanks John

JRozman-delete

My Feedback: (2)

This same thing happened to me with my 3w-75. The halls sensor went bad on mine. When I was trouble shooting I was assured it was not the halls sensor, "they never go bad" I was told.
Well it did. Sounds like that is a strong possibility.

Jess

w8ye

My Feedback: (16)

I understand that if the ground goes bad on some ignitions, (and The ground is through the plug cap or ground strap fastened around the plug), the spark will try to go back through the pick up. Then it's history.

Jim

Diablo-RCU

My Feedback: (1)

Call up Cactus and ask them about it. They likely tested your ignition when you sent it in.
The new ignitions use a Hall sensor, the old ignitions use a pickup coil and the prop needs to spin a few hundred rpm in order to make a spark. It is unlikely the ignition wouldn't have a good ground - it grounds through the metal plug cap and wire shielding.

johnflys1

My Feedback: (3)

Thanks for help guys. This ignition has the hall sensor. Will it spark without grounding the plug against the motor? John

Diablo-RCU

My Feedback: (1)

You should get spark without grounding the plug against the cylinder. The ground is from the plug hex to the metal plug cap then through the wire shield.

mglavin

My Feedback: (31)

In my experience it is very difficult to see the spark. If the ignition was checked out and validated you may have another problem as you well know.

Is the plug fowled?

Sounds like you may have replaced the pickup coil?

Is the cylinder obviously wet with fuel?

Have you verified the power is reaching the ignition module? I noted you deleted the switch, what about a bad wire connector or the like?

Have you cycled the battery with a load and verified the capacity? Even a battery which shows its "HOT" with a DVM may not be able to provide the required current to charge the ignition system.

johnflys1

My Feedback: (3)

Thanks for all the suggestions. I have by-passed the switch. I have tried two different proven batteries. The plug is new and has been looked at in my 3W50 and you can see it firing across the room. I still believe the box or the plug cable must have a problem. This ignition has the little red bulb and it comes on as soon as the prop is flipped, but no fire at the plug. Could it be a ground issue? Remember, it shut off in flight like you turned the ignition off. Have I missed anything else? John

0tter

My Feedback: (39)

Didnt the older style 3W ingnitions have grounding issues? I know a lot of guys with older 3w's use DA or some other type of spark box... Tell Bobby you want a new one (ignition) to test and see if that is the cause. Good Luck!

Diablo-RCU

My Feedback: (1)

The common problem with the older 3W ignitions was that the plug cap insulation would break down over time (and heat). The spark would jump to ground inside the plug cap and not between the plug electrodes.

I'd send the complete ignition, Hall sensor, ignition battery and switch to Cactus Aviation and let them diagnose the problem.