Major hair loss and frustration arising from an intermittent, persistent, and worsening problem with my Lightspeed ignition on my IO-550.  (Magneto on second  system.)  Any help or guesses would be greatly appreciated.

 

The Problem: bad missing on run up when running Lightspeed only.  Missing in No. 1 cylinder, when it occurred, which is irregular.

 

Here is where it gets weird: It only happens when the plenum and cowl are on.  Plenum off: no problem,  Plenum on, sometimes a problem.  Today no problem.  Put plenum and top cowl on: big problem, lots of missing on no. 1 cylinder (not number 2) as evidenced by rapidly rising EGT during the missing.

 

That would seem to suggest cooling air flow is wiggling something around.  If so, we have not found it yet.

 

What we have tried:

·         Switched ignition coil for 1-2, put in new.

·         Switched plug lines between 1-2

·         Switched spark plugs.

·         Substituted new high tension line for  cyl 1.  Seemed to help until we put the cowl back on.  Problem resumed.

·         Ran timing light (cowl off) on all spark plugs, got good clean signals, but then  there was no missing with the cowl off.  We may want to  try again with cowl on and run the  timing light wires out somehow.

·         Checked timing against spec, got good steady consistent signals from the timing light, but again, this was cowl and plenum off.

·         Rerouted all primary and secondary leads with separation from each other and from ground surfaces. ·         Checked all  possible places where wires might rub or  wiggle due to cooling air blast when cowl is on.  Secured all lines with lots of tie wraps to prevent wind driven wiggles.

·         Rerouted all suspicious secondary lines keeping them well clear of everything.

·         Tied all lines down to restrict possibility of wires flopping around under the cooling air blast when cowl is on.

 

Right now, the only really definitive data is:

·         Missing only occurs when cowl and plenum are on.

·         Missing is in cylinder  1, NOT 1 and 2 at the same time.   That suggests a secondary wire fault, but substitutions yielded no improvements. ·         All plugs are new (fewer than 5 hours) and appear clean and new

 

There is only one thing we have not tried (we think): My Lightspeed box is mounted on the front of the firewall, inside of a fibreglass box to which is routed a 1 inch SCAT line that directs cooling air from above the engine into the box and into the little cooling air port  that Klaus puts into his six cylinder ignition systems.  Theory: cowl on, lots of air flow, something is happening inside the box that somehow affects cyl 1 (but not two, which is a mental puzzle as there is only one primary line from the box to the coil for cyls 1-2).  We will try again tomorrow with the cooling air blast tube connected and then disconnected and see if we can find any change, and then it is time to dig into the box.

 

We are really grasping at straws here, and have a pile of straws several feet high that yielded no results.  Any suggestions or speculations welcome.  We may have to hire a mechanic with psychic powers.

 

Frustrated Fred