Ignition Gremlin

[Av8r3400]

As I alluded in the "Milestone" thread, I have been chasing an ignition problem in the Mangy Fox ever since the first start. Because of this, the flight testing has been put on hold.

Here is a description of the problem:

On doing the run-up to 4000 rpm, testing one ignition (A) will drop about 50 rpm. Perfect.

Testing the other ignition (B) gives ~500 rpm drop and the EGTs (located on cylinders 3 & 4) quickly climb through 1500º! Not so perfect.

I have done all the usual stuff.

• Cleaned all grounds
• Checked firing order
• Cut the tips off the plug wires and inspected boots
• New Plugs Gapped to .027"
• Removed modules and checked wiring
• Removed, cleaned, rebuilt, synchronized carburetors
• Then I did it all again...

I spent time today speaking with tech support with CPS, LEAF and Lockwood. The guys at Lockwood cam up with the theory (and they have seen this before) that one of the modules is malfunctioning and could be firing one side 180º off. This would cause the problem I'm seeing.

Each module fires a coil every 180º of crank rotation and each coil fires a pair of plugs (1 & 2 top, 3 & 4 bottom, etc.). If the module is malfunctioning and firing both coils at the same point, then one pair of plugs will ignite the fuel on the way out the exhaust valve, causing the EGTs to skyrocket.

[Av8r3400]

I sent the modules off to Lockwood today to have them tested. (Lockwood is the only place in the US with the testing machine for them)

I have mixed feelings on this. If the module is bad, it will cost me $1200 for new one. If the modules are good then I've got absolutely no clue what's wrong. (But I'll still have money in my account) That's either a win-win or a lose-lose, I'm not sure...



I've heard that kidneys are selling for about $1500 these days.

[HighWing]

"Checked firing Order". Not sure what this means. Would this check have detected the 120 degree off Lockwood is suspecting? The first thing that came to my mind is the possibility that the 1 - 3 or the 2 - 4 lower plug wires might have been switched. Do you have the yellow tags on the ignition wires?

[WWhunter]

Not sure if this makes much differnce, but I thought the plug gap was supposed to be set around 0.021". I need to go check my Zipper plugs I guess.

I just seem to recall there was a 'tighter' gap with one of the piston sets. I do recall the 95 HP Extra-Performance pistons suggested a smaller gap than factory.

[Av8r3400]

When I say check the firing order, I mean the routing of the plug wires to the proper coil. That also means checking that the coils were wired properly to the correct ignition module wires and the plugs were hooked to the proper coils. Thus eliminating the possibility of 1/3 and 2/4 wire mix ups.

Rotax calls for .028" gap on plugs.

[WWhunter]

Yes sir, it was the plugs on the 912 XtraPerformance pistons I originally had in the motor that needed a smaller gap.
www.craftworks.biz/pistonsite/6318.htm

[Av8r3400]

It's a Good news - Bad news situation today.

Good news is that the modules checked out fine down at Lockwood.

Bad news is now I have no idea what the problem is…

[gregsgt]

The EGT climb doesn't make sense to me. Dropping a mag should make the mixture more rich and EGT's climb when the mixture gets lean...

I think it sounds like a wiring problem in the ignition somewhere. Maybe a bad switch or something.

[Slyfox]

this is my thoughts. when you get your modules back, switch sides, see if it changes to the other side, if not, electrical wiring

[Dave S]

Larry,

Don't know if this would help any; but, on single ignition engines timing can drastically affect RPM. If everything else is equal (thottle the same) advanced timing will result in a higher RPM......retarded timing will result in a lower RPM...retarded timing taken to the extreme (short of killing the engine) can also result in a big RPM reduction with the charge burning partially on the way out of the engine which would possibly raise the EGT.

When you mentioned 50 and 500.....the 50 almost seems like less of a drop than a person would normally get on Rotax. If considering timing....is there any chance that the side which drops off 500 and raises the EGT is running on a severely retarded timing setting?

I don't have a clue how timing is controlled on a Rotax. Don't recall if you have the soft start (which I believe retards the timing to prevent kickback) and I don't have any idea if there is any possibility of the soft start affecting the running mode.

Again, not saying that I know anything about what the problem is; but, thought I wanted to share this possibility in case it might play into the issue.

Wish you luck in solving this.

Dave S