Ignition Problems. Help??

[J12345T]

Hi All,

The engine is running like a bag of bolts when selected to the R side ignition system. Engine runs fine on L and seems OK on Both.

The problem is somewhat intermittent in that a flight in the morning displayed the problems and I couldn't fly whilst the (trouble shooting) flight in the afternoon was fine. A couple of weeks later same problem.

Aircraft is now with the maintenance provider looking for the problem/ solution. So far we've removed the cowls, checked the plugs, swapped the plugs, checked the coil harnesses, checked the coil wiring resistance, checked the timing sensors. Only issue found was that those crappy spade terminals on the coils were a bit lose. They were 'tightened' but the problem remains.

I should also say there is no engine monitor of any description fitted (yes I know).

We're going to change out the spade terminals for something more aviation appropriate but that is a long shot.

Can anyone tell me which coil controls which spark plugs by any chance as they're not marked at all...

Any other suggestions much appreciated.

Cheers,

James.

[Daveembry]

165FD5F9-BFC0-4EBD-8609-E3B3CCF70A28.jpg

That’s too bad you don’t have any sensors??? You don’t have EGT or CHT probes? If you did, look at each cylinder EGT (or CHT) when you go to the R ignition. The cylinder with no egt or low egt will show up immediately. If it’s running OK on BOTH, then sounds like a coil, plug, spark plug wire or mini-sensor (or box but unlikely).

I don’t think it’s fuel related (like injector clog) because it would be the same regardless of which box you select.

Here is a link to a forum post I did explaining the ignition system problem I had once http://forum.cubcrafters.com/showthr...ll=1#post23176

4. Ignition system and mini-sensor. This was a pretty interesting situation. Back in the post when installing the G3X wiring and the wiring harness in general, I tested almost every wire going “somewhere” light lights, trim motor, etc. but as mentioned before.......not the trim sensor and I didn’t ever test the ignition system other than to test the wiring per the instructions on the operation of the switch, backup battery systems, etc. but I didn’t think of .......or know of a way to check to see that the mini-sensors worked...........and I wished I had..........and I will in the future.

Here’s what happened:

On the first engine run-up the engine fired right up and ran fine. I did a quick ignition check........on BOTH......ran fine. On LEFT.......ran fine. On RIGHT..........bam.........really bad miss and huge drop in rpm’s.

I switched to LEFT and looked at EGT’s and all showing green but when I switched to RIGHT......... cylinders 3 & 4 EGT’s dropped off to nothing. Here’s the procedure I used to work out the problem.

Understanding the ignition system, here is how it works. The RIGHT ignition box has 2 cables going to 2 coils at the bottom side of the engine and this box fires the BOTTOM spark plugs in the engine. The LEFT box goes to the 2 upper coils and fires the TOP spark plugs.

So on the 2 bottom coils that are controlled by the RIGHT box, the pilot right side coil controls bottom cylinders 3 & 4, which are the ones I had a problem with so I first suspected a coil problem so I swapped that coil out with the coil on the bottom, left side (that controls cylinders 1 & 2) and the problem did NOT move to cylinders 1 & 2 but stayed with 3 & 4........so this eliminated that it was a coil problem.

When I experience a problem, it’s seems it’s usually the simplest thing that causes it so I always look at the simplest things first before going to the hardest. In this case I'll test..... the coil, spark plugs, spark plug wires, ignition wires, mini-sensors and lastly........the ignition box.

Coil eliminated so i next checked the spark plugs (fat chance that 2 plugs were fouled at the same time ....right?)and they looked fine but I went ahead and put 2 new ones in anyway.

Next I did a continuity check on the spark plug wires going to these 2 cylinders (fat chance that 2 spark plug wires were bad at the same time.....right?). All good.

Next I removed the right, forward interior panel to expose the ignition boxes and I had previously labeled each box as RIGHT and LEFT by writing this directly on the boxes with a sharpie. The left side box was the LEFT side box so I removed the right side RIGHT ignition box ignition wires (BNC connectors and on the forward side of the box) and did a continuity check with the positive side of the connector at the coil (blue connnector attached to the center wire of the cable) and the center of the BNC connector and the negative (yellow connector) with the outside of the BNC connector. I really thought I might find the problem here where I had installed the connectors but it was all good.

Next I double checked the mini-sensors I installed at the flywheel to be sure the gap was correct. The tolerance is .030-.060 from the flywheel being sure it stays parallel to the flywheel across the mini-sensor. They tell me that the closer to the minimum gap the better, so I used .032. All good.

Next....... crap.......guess it’s the box and it doesn’t look like fun removing that bracket. Mitch and CC was great and overnighted me another box and instead of actually removing the existing boxes, I just attached the connectors to the new box temporarily to test it. I didn’t bother removing and installing the yellow manifold pressure lines from the existing box to the new box because it wouldn’t affect the engine running.........it only affects the engine timing. NOPE.....not the box!!!! NOW WHAT?

OK....emails out to Klaus who owns Lightspeed. It was amazing.....it was a Saturday and i didn't expect to hear from him at all.....much less on a Saturday.....but within an hour or so he replied and said..... “our boxes and mini-sensors never fail” and he suggested running the tests listed in the Lightspeed manual that comes with the system (and from CC). I looked them up and pulled the INPUT cable from the back of the box and checked the pins listed to see if power was coming into the box from the aircraft wiring harness........... ALL GOOD!

OK....NOW WHAT?

Has to be a mini-sensor right? But Klaus says they never fail. Only problem is I know a guy who did have one bad so I knew they could be bad. If you recall, there are 2 mini-sensors installed 180 degrees apart from each other up behind the flywheel.........1 for each for the LEFT and RIGHT ignition boxes. The sensor on the RIGHT side of the engine is for the RIGHT box (and my problem area). On the aft side of the flywheel there is a plate that is installed that has magnets in it. These magnets are picked up by the min-sensors as the engine rotates and this signal passes from the sensors to the ignition box which decides when to send a signal to the coils to fire.....which then goes through the spark plug wires to the spark plugs ......and the engine fires. This timing of the firing is changed by the ignition boxes and the changes are based on a multitude of data.

Digging into it more, I discover that each “mini-sensor” unit is actually comprised of 2 sensors in the housing.......1 that is for the cylinder 3&4 coil and the other for cylinder 1 & 2 coil. So my 1 & 2 side of the sensor is working but the 3 & 4 side is not???



(This mini-sensor is really a housing that contains 2 separate sensors....each with it's own wire going to the connector)

Once again Cubcrafts comes through and overnights me a new sensor to try (even though they never fail........).I’ve got the new sensor and see that the cable is long enough that I can install it on the right side of the engine and just run the cable on the outside of the plane to the box inside to just test it before actually going though the hassle of getting it thought the firewall clamshell, etc.

So I remove the existing connector from the right sensor where it goes into the ignition box. I’m inspecting the wires going into the connector and see that there are 2 wires coming from the sensor into the connector, no doubt 1 from each side of the mini-sensor so 1 is for that 3 & 4 coil and the other for the 1 & 2. Hmmmmmm.......what if......



(These 2 wires are coming from the mini-sensor to the 2 pins that are side by side.)

Yep.....with my magnifying glass, I look very closely at the solder connections Lightspeed has made where the wires attach to the connector.....the pins are side by side and looking closely, I see a bit of solder has bridged the 2 pins and I’m sure that shouldn’t be. A soldering iron to melt the solder and a small piece of sandpaper between the pins and it’s all back together and working great! What a relief but it has taken me almost a week to get this one sorted out.

SO......... in keeping with my #3 item on the problem solving list above on how to deal with problems..........how can I test this in the future when installing the engine/wiring? Believe me........I DID NOT WANT TO HAVE TO CHANGE OUT AN IGNITION BOX after having looked up there and seeing how hard it was going to be to access the bolts/nuts/clamps. I will also change the way I install the ignition boxes in the future to make it easier if I ever have to (and will discuss that later below).

So from now on, I will test the mini-sensors/ignition boxes, etc. Looking at the Lightspeed manual, there is a test you can do that will show if a signal is passing from the sensors to the box when a magnet passes by it. i think this can be done while wiring the units and before installing the boot cowl. Essentially, you remove the input connector from the box that is coming from the sensor. The manual shows which pins to attach a meter to and when you pass a magnet (maybe a magnetic pickup tool?) by the sensor, you will see voltage show up. CC has the power wires, etc. they have installed into this connector that you have to connect into the wiring harness, so be sure when you test that those wires are connected to the wiring harness and that you have master switch on and battery power of course.

Another test of the system once you have the engine installed (prop can be on or off)......either remove all the spark plugs (especially if no prop on and you want to turn the engine over by hand using the flywheel) or remove the spark plug wires from the spark plugs. Also remove the spark plug wires from the coils. With the master switch ON and the ignition switch on BOTH, turn the flywheel around quickly and you should see the 4 coils “snap” or fire/spark each time the flywheel magnets pass the sensors. All 4 should work.

Hi All,

The engine is running like a bag of bolts when selected to the R side ignition system. Engine runs fine on L and seems OK on Both.

The problem is somewhat intermittent in that a flight in the morning displayed the problems and I couldn't fly whilst the (trouble shooting) flight in the afternoon was fine. A couple of weeks later same problem.

Aircraft is now with the maintenance provider looking for the problem/ solution. So far we've removed the cowls, checked the plugs, swapped the plugs, checked the coil harnesses, checked the coil wiring resistance, checked the timing sensors. Only issue found was that those crappy spade terminals on the coils were a bit lose. They were 'tightened' but the problem remains.

I should also say there is no engine monitor of any description fitted (yes I know).

We're going to change out the spade terminals for something more aviation appropriate but that is a long shot.

Can anyone tell me which coil controls which spark plugs by any chance as they're not marked at all...

Any other suggestions much appreciated.

Cheers,

James.

[Dan L]

I wonder if it could be in your key switch? Or a bad breaker from the battery?

[Dan L]

If you have more than 500 hours on this O-340 I'd suggest changing out the coil leads. I had a similar issue and that fixed it. They're about $20 each so not a big deal.

I also had a loose spade connector later that caused misses. It still baffles me that these little spades are being used for such an important task.

[Andy]

Any other suggestions much appreciated.

Have you followed the trouble shooting flow documented on page 39 of the Plasma CDI installation and operation manual?

[J12345T]

Hi All,

Thanks so much for your responses.

Dave; yes I have read and re-read your extremely detailed and helpful post. More info there than I found anywhere else so thanks again. I'll take a close look at the mini sensor plugs.

Dan; thank you yes, the engine has around 500 hrs on it but it is much older than the 3(?) years recommended so replacing the leads is something to do for sure. It is that hard of a job?

Andy; yes we've been though the troubleshooting guide but with no EGT/ CHT's its not easy to determine much.

Interestingly the picture of the EX Cub's coil installation is very different from what I'm looking at. The ones in this engine are located in a row under the front side of the oil pan. It would help if they were marked..

Anyone know if it would damage anything to do nothing else but swap the connector leads for the brain boxes? I'd like to know if the problem stays on the R side or migrates with the box..

Many thanks again.

James.

[Andy]

yes we've been though the troubleshooting guide but with no EGT/ CHT's its not easy to determine much.

No test in the referenced trouble shooting flow requires EGT or CHT instrumentation. What you do require is an ignition timing strobe light and a DVM or similar.

[Daveembry]

Here is the one I was referring to at supercub.org but it was doing it regardless of ignition switch position. But, there is lots of good info in the thread if interested:

https://www.supercub.org/forum/showt...n+cub+ignition





When I was troubleshooting mine, I was told I could swap the leads on the boxes to test. Also, go look on Supercub.org and Steve Pierce. I recall a long thread he did with a problem he had a hard time resolving but finally got it figured out on a Carbon Cub. I don’t recall the specifics but it may have been another engine problem disguised as an ignition problem as I recall?????

Be sure to check the timing ring mounted on the back of the flywheel ....that’s its not loose and that any of the magnets are loose or maybe missing? Be sure the min-sensors are tight and the correct distance from the timing ring and is parallel to it and not angled.....no damage to the wires around the mini-sensors, etc.

The egt’s on all cylinders are so nice to have. When I do run ups before takeoff, I always bring up the engine page in the window so when I switch between L and R ignitions, I can look at all 4 cylinders EGT’s when I switch. It will show you immediately if there is something going on in one half of a cylinder. In the BOTH positions, even if you have a problem with one side of a cylinder, the box will mask the problem and you can’t tell you have a problem except you will see a big variance in egt’s/CHT’s in the affected cylinders.

Good luck with it.

Hi All,

Thanks so much for your responses.

Dave; yes I have read and re-read your extremely detailed and helpful post. More info there than I found anywhere else so thanks again. I'll take a close look at the mini sensor plugs.

Dan; thank you yes, the engine has around 500 hrs on it but it is much older than the 3(?) years recommended so replacing the leads is something to do for sure. It is that hard of a job?

Andy; yes we've been though the troubleshooting guide but with no EGT/ CHT's its not easy to determine much.

Interestingly the picture of the EX Cub's coil installation is very different from what I'm looking at. The ones in this engine are located in a row under the front side of the oil pan. It would help if they were marked..

Anyone know if it would damage anything to do nothing else but swap the connector leads for the brain boxes? I'd like to know if the problem stays on the R side or migrates with the box..

Many thanks again.

James.

[JohnC]

I had the same symptoms a few years ago. All ground checks were fine. During cruise, I could feel a little roughness in the engine. Engine monitor confirmed, one side of the ignition system had two cylinders intermittently firing. I ran it down to one of the flag connectors on one of the coils had several broken wires. I replaced the connector and that solved the problem. I then potted all the connectors. Now the wires are secure and protected.

[mikemacon]

James -

The symptoms you describe appeared with my engine at 600 hrs. It turned out to be a burnt intake valve. Because the miss only occurred on one ignition, my mechanic and I chased the ignition system for several months with the help of Lightspeed and CubCrafters. After giving up, and changing out both ignition systems, the plane was flown to Yakima on the “good” ignition. Within a few miles of Yakima it momentarily failed on the “good” ignition. CubCrafters went through the ignition systems in their shop. They could not find an ignition problem and started looking elsewhere. They found a burnt intake valve in cylinder #1.
I had another fail with the same symptoms at 650 hrs. but I knew what was happening this time. We scoped the cylinders and found another burnt intake on #3.

Good luck.

I probably should have checked out Dave Embry’s post before I responded. The Supercub.org thread he directed you to has my info in post #69. And yes, in my case the failure initially was only on one ignition. Both times.