9912ULS Ignition Module Issue, maybe

Hi Scott

There is no ohm check for the modules.  You can only check the ohms for the triggers and charge coils.  The "P" leads are energized when the engine runs, your shut off is to ground these to the aircraft and in turn that goes back to the engine.  The system is a normally hot system in that the only way it will stop giving power to the spark plugs is to ground the P leads.  Check you have ground from the engine to your airframe and that each switch is grounding.  If this is a standard 912 system just switch modules from A to B and try it again.  If the problem follows the module it may be a module problem but if it stays on the same one you have some other wiring issue.  Check the heavy maintenance manual for the complete wire diagram. 

As a note.  ACS switches can give you problems, be sure that the switch itself is not dirty on the movement from A to B and both.  Sometimes the wafers on the switch get contaminated. Do a good check of the switch before you spend a ton of money on a new module. 

Cheers

Scott

Perhaps this will help....see ACS info on servicing the switch. 

Cheers

It is not uncommon for the kill circuit in the modules to go faulty. I've had 2 with this failure mode myself. The input to this section of the circuit consists of an inductor in series with a resistor before it then splits into another resistor network and a transistor. The input resistance is dominated by 1.8 ohm resistor in series with a 270 ohm which in turn is in series with a 22 ohm and the inductor. The total resistance looking in with respect to ground should probably be about 300 ohms.

I've just measured a couple of the 4-pin modules that I have here, one of which exhibits the same fault as yours. They both measure about 295 ohms between the kill input and ground. I am not sure that any of this helps your situation. If you are measuring completely different resistances on the 2 modules then you definitely have a problem with one of them.

Over here in the UK many owners have now changed over to the Ignitech modules as they seem more reliable and are significantly cheaper. They also offer the benefit of using 12V power to power the module during starting, after this they use the Rotax charging coils.

I’ve seen the Ignitech site and wondered how well their stuff works.  I’m certainly not opposed to trying their modules out but I’m not exactly sure how to adapt it to my engine.  Meaning, if it isnt plug-n-play I would need a good wiring conversion diagram.  Before I commit to any solution I need to get my modules tested first.

There is good support from Ignitech and the modules come with an adapter harness so that it just plugs in. The only modification is if you want to take advantage of the 12V supply during cranking. Many of the owners who have installed them in UK fit them on the cockpit side of the firewall to keep their temperature down. This will certainly improve reliability and prevent any electrolytic caps from aging. The new harness is long enough to allow this modification if wanted.

If the fault moves with the module when swapping them over then it is almost certainly faulty

There are some pictures here.

Here is the approval information from the UK Light Aircraft Association and the BMAA.