Intermittent engine start failures

[FWombat]

I'm trying to track down some intermittent starting problems -- hopefully some expert eyes can spot the problem!

Engine is a Honda K24.  About half the time, the engine fires up and idles smoothly within a few cranks.  The other half of the time the engine turns over but doesn't start, often with a nice loud backfire.  The backfire makes me think trigger sync problems but so far I haven't found anything interesting the logs.

I've captured a log with a some successful and failed startups.  I've also got scope captures of both successful and failed starts.  

Trigger Scope - successful start.llgx Trigger Scope - failed start.llgx Trigger Scope - failed start 2.llgx failed start in middle.llgx After dyno take 2 - new triggers.pclx

[Adamw]

It looks like you have trigger 2 wired to the intake cam, it needs to be the exhaust cam.  The Intake cam has 4 evenly spaced teeth so this gives no unique event that the ecu can synchronise to.  Right now you are syncing by luck of the draw.

The exhaust cam on the other hand has 5 teeth, so the ecu will see 3 teeth on one crank rev and 2 for the next crank rev so it knows what phase it is in.  

The intake cam sensor should be wired to digital input 1-4 it this engine has VVT.  

[FWombat]

You almost nailed it!  Turns out the wiring was good -- trigger 2 was correctly on the exhaust cam sensor.  The problem was that the trigger wheels were physically on the wrong cams.  Swapped the trigger wheels between the cams and now it starts like a champ.