Starting difficulties IO-360 Superior

[BillOrcutt]

Anyone having starting problems, cold or hot, whereby the engine fires just as you release the ignition switch or starter button? My setup is Aerosport IO-360, 180 HP, Bendix, Slick mags, GRT Horizon EFIS/EIS. I've replaced the ignition switch, left mag, and traced ignition wiring ad nauseum, but can't find the cause of my frequent lengthy cranking, that only fires when releasing the switch back to "both." Had the problem 2 years since new, in my -7A, and just learned of another -8 with same problem, on the field. (not a hot-start procedural issue) Possible cranking "speed" issue? Thanks!

[Webb]

Just a guess but it sounds like the mags are grounding out when the starter is cranking. Release the start switch and no more ground.

Perhaps one of the Van Heads out there can tell you how to test it with a volt/ohm meter.

[asav8tor]

I assume your mags are wired for the right to be grounded and the left to not be grounded when the starter is engaged. Is that correct?

If yes, then,

For whatever reason the the left is not firing when the starter is engaged. In fact it might not be firing when the starter is released in which case the engine is running on the right mag only when the starter is released.

You mentioned that you traced the wiring, replaced the left mag, etc. If you have a shielded wire going to the left mag check the wire shielding at either end or anywhere along the way is not shorted to the center conductor.

Starting at the left p-lead stud/nut on the mag, the question to ask yourself is the problem on the mag side or the wiring side?

This is really not a great way to trouble shoot because it creates an unsafe condition with a hot mag but you could disconnect the p-lead from the left mag and crank it. Should start while cranking. In this case you will have confirmed you have a wiring problem. If it doesn't start while cranking you have a mag problem.

[Jamie]

I agree with the above.

This should be an easy problem to diagnose (easier said than done, right? ).

I would disconnect the mag wires and try to start it. If it fires that time in the start position, you KNOW it's a wiring problem. If it doesn't, you KNOW it's a mag problem.

Next I would disconnect the starter contactor wires, then put a multimeter on the mag wires. Check all five positions on the key switch, OFF, R, L, BOTH and START. With regard to the mag wires, they should be identical in the BOTH and START position if you have dual impulse-coupled mags. You mentioned that you replaced the left mag? Do you have the little jumper installed on your keyswitch for disabling a mag if you only have one impulse-coupled mag? If you have two impulse-coupled mags of course this jumper should not be there. You should be starting on both mags. I have the same same setup on my XP-360 w/ slick mags. Prime for three seconds in winter, 5 seconds in summer and BAM...that thing fires up with no hesitation whatsoever...always on the first or second blade.

Right now I'm wondering if you're every really running on both mags. It wouldn't be unheard of. One of our local guys flew his entire Phase I on one mag due to a wiring problem. Do you notice an RPM difference when you switch between the two mags?

With the engine idling, I would also briefly switch the key switch to off to see if it actually tries to kill the engine.

This problem is gonna bother me all day.

[allbee]

or you can throw the ign. switch and install individual switches for the mags. just a thought.

[Jamie]

Originally Posted by allbee

or you can throw the ign. switch and install individual switches for the mags. just a thought.

I knew that someone was going to suggest this. I think before he does that and ends up having the same exact problem he should actually know what the problem is. There are certain advantages of using individual toggles over key switches, but this is not one of them.

[RV8iator]

Originally Posted by Jamie

With the engine idling, I would also briefly switch the key switch to off to see if it actually tries to kill the engine.

Off topic here, but every time I taxi up and get ready to shut down I quickly switch both mags off to make sure the engine really will quit. Unless it breaks while cranking I know both my mags will shut down on every flight.

[allbee]

Originally Posted by Jamie

I knew that someone was going to suggest this. I think before he does that and ends up having the same exact problem he should actually know what the problem is. There are certain advantages of using individual toggles over key switches, but this is not one of them.

I agree, but if he does remove the wires from the mag and it starts good, he can either, make things easy and install switches and a starter button. Or he can pull his hair out and figure what was done wrong with the key switch. I have this set up in my flying airplane and I loooove the individual switches. I put in in my 7 panel. Now if it ends up being outside the electrical, fine, he moves on to the next thing. I know my kitfox will start like this and it's all in the fuel carb system. What I do is put full off on the throttle as I'm cranking it and slowely put in the throttle until it starts. If I put the throttle on some and hit the start, it has troubles, not saying is what is going on here, but anything is possible.

[Mike S]

Originally Posted by RV8iator

Off topic here, but every time I taxi up and get ready to shut down I quickly switch both mags off to make sure the engine really will quit. Unless it breaks while cranking I know both my mags will shut down on every flight.

Yep, old timer taught me that trick long time ago.

And, considering my starting procedure was to prime, then pull the prop through a couple of turns, sure was nice knowing the mags were in fact "Cold"

[Jamie]

Originally Posted by allbee

Or he can pull his hair out and figure what was done wrong with the key switch.

My point is that checking the wiring with a multimeter at the mags is exactly the same as checking the wiring with separate switches. Key switches are extremely easy to troubleshoot.