Secondary Ignition Troubleshooting

[Brett]

I need to chase down a fault this week with my secondary ign. Was all strapped in for a hamburger lunch with 2 other planes and the secondary ign circuit breaker kept popping out after about 10 seconds. Won't pop when engine off, only running. Hungry pilots resulted in me only having time to check the wiring visually. Will have time during the week or next weekend to diagnose properly. Had to get a ride in another plane and leave mine in the hangar broken and lonely. Would be nice if it's just the circuit breaker and not a fault with the ign system.

Ironically I'm also needing to change out my second primary ign coil. My lower one died on the first early flights and had no spark, my top one now still operates fine but won't switch off. Hoping for some trouble free flying soon.

[gammaxy]

Does the circuit breaker pop at idle? Does it run long enough that you can turn off the primary and see if two cylinders aren't firing on secondary?

You might want to be sure your voltage regulator circuit is fine--I could imagine the fuse blowing if unregulated voltage from the alternator is ending up at the secondary ignition modules.

I'm doubtful that the problem could be one of the coils. Each one is ~3 ohms, so you'd need over 15 volts from the battery in order to blow a 10 amp fuse if they were constantly energized. I'd probably still measure them to be sure, but it would have to be a strange short inside to cause a problem and I'd expect the CB to pop immediately after the circuit is energized.

With your primary ignition, you might try eliminating the wiring/switch as a variable by directly connecting the P lead to ground at the module.

[Brett]

Yes the circuit breaker pops at idle after about 10 secs. With the engine not running its fine. The engine runs fine on either ign till the circuit breaker goes. However as the top primary coil won't shut down it's a false test as the primary could be running the top plugs on the cylinders that may be dogey on the secondary ign on the lower plugs if that makes sense.

Tonight was the only night this week I could look at the plane so I went out there only to remember I needed a second person to undo the bolts from the other side of the firewall to gain access to the secondary coils hex head bolts. Doh. I assume the wiring needs to be off the coils to check them properly with an ohm meter. Oh well so anyway I took the top primary ign coil off so when I get the new one tomorrow I can just fit it on the weekend. Least then the primary's will be good and then can concentrate on the secondary Ign. Still hoping it may just be the circuit breaker or something simple. Strange on this Aerovee I've had nothing but trouble with the ign system but on my old one the ign systems never gave me one second of problems. I'm sure I have just ran over a black cat is all.

[radfordc]

Could be a failed trigger module. I had that happen and it did blow the secondary fuze. The engine would start and run fine on the primary. In fact I flew all the way home from Crossville, TN on just the primary.

[Fastcapy]

I also had a bunch of issues with the ignition system on mine. In 50hrs I went through 2 magnetos, a trigger and a coil.

After the second (both were the top one) magneto failed in such a short time I talked with Briggs about the failures and they figured that the top one was getting too hot because there wasn't a lot of cooling airflow over it mounted behind the baffles. I put a blast tube on it and it has been fine for the last 50hrs.

The coil and trigger I have no clue on as to why they failed.

So it is easily possible to have failed components in that short of time.

[Dennis W.]

Would appreciate where to find details on how to check secondary ignition coils and ignition triggers....how to test, ohm readings, etc. My secondary failed today and fuse was not blown so assuming its a bad coil or trigger. Also if anyone has instructions on how to test alternator. Tac quit too plus voltage drained. All wiring looks good so assuming alternator quit. Bad day for electrical issues but did make it back to my home airport safe and sound.

[gammaxy]

Dennis,

That's a lot to go wrong in the same flight, I'd assume all problems are somehow related. In this case, I'd expect that whatever was involved in the alternator failure removed the secondary ignition from the circuit.

Is the entire secondary not working? Over time, I've had 3 bad coils, but I've never lost more than 2 cylinders on the secondary at a time. The first two prevented the plugs in two cylinders from firing. The final failure somehow only prevented one plug from firing. For checking the coils, measure the resistance between the 12v terminals on the top to see if it matches the labeled 3 ohms. Then measure the resistance between the high voltage terminals--it should be tens of thousands of ohms, but I forget the exact value. Then measure between the high voltage and low voltage terminals. I believe this should be an open circuit. One my most recent failure, it was around 1MOhm.

For testing the triggers, it's probably best to just attempt to use them as intended and see if they output 12v and drop to 0 whenever a magnet moves by. I did this on my workbench, but if you're careful it can probably be done on the airplane. I've never had a trigger failure so tend to be suspicious of the coils.

[Dennis W.]

Chris, thanks for the follow-up. Secondary went out first but only lost 2 cylinders. Did see some crazy voltage swings when it failed. I turned off the secondary and voltage quickly came back up. All seemed well for about 10 mins and then tach went to zero and voltage started dropping. I have an alternator cut-off switch so assumed alternator had quit and switched it off. By that time I had made it back to my home airport so focus was on emergency landing in case the engine quit. Back at the hangar I pulled the cowling and chased down the wiring but all looked OK. Thanks for the test info so will begin the process to see if I can find where the problems are. But I'm close to being at the point where I'm done with flying behind a VW. Too many maintenance issues, chasing hot #1 and #3 EGT's and CHT's, burnt valves, and constant valve adjustments. If feels like I fly 1 hour to then work on it for 5 hours.

[kmacht]

If the tach quit and the voltage was dropping it is most likely your voltage regulator that went bad. It is a common failure point on this engine due to the heat and vibration firewall forward. The tach pickup on an aerovee is almost always off one leg of the regulator. I would be willing to bet that the low voltage is also what was causing your secondary to quit. A search on the forum here will turn up a briggs and stratton regulator the same size and specs but with a larger heat sink and cooling fins. I seem to remember it being around $25 on amazon.

Keith
#554

[Dennis W.]

Keith, If the voltage regulator failed vs. the alternator, seems that the tach sense would still work since the pickup is on the input to the regulator (output of the alternator) vs. output of the regulator. I had a voltage regulator failure about a year or so ago and did not see a tach failure, just low to no voltage pickup. Now running a Harley Davidson regulator and it has been working great. But I agree that the regulator is a potential problem area due to heat and vibration