After fire from Wasted Spark Ignition

[barryrv10]

I have an Electroair EIS ignition which uses wasted spark coils on an IO-540 and it has been great for 300hrs. When starting today I got what I think was an after fire (ignition on the exhaust stroke) just prior to a normal start. I can see this happening if conditions are just right; like the old days when we would turn the ignition off then back on and get a "backfire"

Since this is a first for me, has anyone else with wasted spark ignitions had any similar problems like this when starting. I did not have a kick back, just a loud firecracker like bang then a normal start. Thanks Barry

[vlittle]

Originally Posted by barryrv10

I have an Electroair EIS ignition which uses wasted spark coils on an IO-540 and it has been great for 300hrs. When starting today I got what I think was an after fire (ignition on the exhaust stroke) just prior to a normal start. I can see this happening if conditions are just right; like the old days when we would turn the ignition off then back on and get a "backfire"

Since this is a first for me, has anyone else with wasted spark ignitions had any similar problems like this when starting. I did not have a kick back, just a loud firecracker like bang then a normal start. Thanks Barry

The EIS fires cylinders in pairs. A fouled plug in one cylinder can affect the spark in the other cylinder. If it fails to ignite, the unburnt charge may ignite during the exhaust stroke or in the exhaust. Check the plugs. If they check out, remove all of the plug wires from the coil pack and crank the engine. You should see sparks between the coil turrets. You may need a partner to observe this.

All of the coils should spark the same. If they don't, you have a bad coil. It's a GM Part, available anywhere.

[rv6ejguy]

Been flying and driving waste spark EI systems (SDS) for about 20 years and never had this happen but this is with EFI also. Might be possible with a dripping wet carb to hose enough fuel into cylinders that it doesn't fire. The fuel then goes into the exhaust and maybe ignites on the next stroke. Alternately there is a possibility of interference (maybe from starter current) messing with the microprocessor and screwing up the timing. Funny it would start to do this after 300 trouble free hours. A bad plug wire also generates tremendous noise potential which could glitch the micro again.

With any waste spark system using the GM D555 coils, it's a bad idea to check spark between the towers. They will generate over 45,000 volts and this will try to find a path- often through the coil windings internally which can damage the coil.

Wrap some bare wire around one tower and leave a 1/4 gap to the adjacent tower if you must test for spark.