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Help! Ignition system failure


opticsguy

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This one has me stumped. I flew two weeks ago at night to get current. Shut down as usual and put it in the hangar. This was two weeks ago. This morning I go out to fly and it won't start. No spitting or backfires (it was 62F)...nothing. Ran the battery down, hooked up my Blazer and tried some more...nothing. It doesn't seem to be a fuel problem.

 

I took out a plug, grounded it, and looked for a spark. Nothing. Held my fingers over the plug and cranked the starter...nothing, no shock.

 

Other than the thunderstorm a couple of nights ago, nothing should have bothered my plane. Neither of the two mechanics that work on my engine have heard of anything like this happening.

 

We're out of ideas.

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Hi Optics,

 

Since you haven't done anything to the plane since you flew it last then any maint issue is out. The engine has to turn around 240 rpm to produce enough electricity to fire through the coils. If it only turns 200 it won't fire or have a spark and you wouldn't be able to tell the difference. 95% of the time this is the problem. Get a new or fresh battery and hook it up. Then try again.

 

If the engine is turning over fast enough then the stator is turning at the trigger coil pick ups. If it is turning fast enough it has to produce electricity and since it is a duplicate or redundant system then at least one would work even if the other is not.

So if it is turning fast enough it has to produce electricity going somewhere.

 

One last thing, if you flood the engine which is easier to do in this weather then it will turn as you describe and not fire until it has cleared out. You also must rule out the fuel starvation issue.

 

This will end up a simple fix so don't take any thing for granted. Something has been missed.

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Clearly, the simplest explanation is the most likely. I should mention that I squirted some fuel into one of the carb intakes and cranked it, and still nothing. This was with a fresh battery and the prop spinning like I had never seen it.

 

In the past my engine has started when the battery is on it's last legs. This behavior is very different from what I've seen in the past. This is making me re-think Oshkosh this year.

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How does the CT ignition switch work?

 

You can easily find the "P-leads" or equivalents at the multi-pin connector going into each ignition module and see if somehow they're each grounding through the switch. I can imagine a switch failure that could do this. Thinking of it, it might be easier to check at the switch - in the "BOTH" position, if you have one, neither lead coming out of the switch should be grounded.

 

I had to do this when I installed my SoftStart module - I have separate ignition toggle switches and I needed to see which switch grounded which module.

 

Just a thought...

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I had a similar starting problem on my plane after not flying for a couple weeks. The problem was traced to a broken wire between the top ignition module and the white plug. It was hard to spot and was found by feeling along the wire insulation. A solder repair was tried, but unfortunately it took a new module to solve the problem. My engine did not want to start on just one ignition circuit.

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My engine did not want to start on just one ignition circuit.

 

Interesting data point.

 

The ROTAX 912ULS2 in my Sky Arrow will start just fine on one ignition circuit. I had tried it in the past as a solution to hard starting and kickback, and while it didn't help, it didn't hurt, either. With the SoftStart module installed, starting on one ignition is SOP.

 

The key here is each ignition circuit is designed to be totally isolated from the other. No single failure should take them both out at the same time. Thinking logically, the only single-point failure I can think of is still the ignition switch - it should be the only place where a catastrophic failure could take out BOTH ignitions.

 

Or, as in the linked thread, a wire harness that somehow grounded out BOTH "P-leads"* at the same time - hard to picture, but possible, I guess.

 

 

*I believe "P-lead" is short for "PRIMARY-lead", and refers to wires that ground out the primary windings of a magneto. With the CDI of the ROTAX, it is not grounding a winding but an ignition module. Different animal, but I think "P-lead" will be clear enough, just as "choke" is.

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My number one vote is one of the wires on top, too. I have just seen that scenario too many times to not look there very closely first. I prefer to relocate the wires when I do firewall blankets or hose replacements out from under hoses and put then a little more on top of the hose so the hose doesn't sit there and chafe the wire against the air plenum.

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I checked the switch with an ohmmeter, and it seems to be OK. Nothing looks terribly wrong with the wiring, but I'll give it a closer look. The only other thing I since the last time I flew was to take the 496 out and update the software and re-install into the panel. I've had some wiring harness fraying issues in the past.

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Optics,

 

When I find a bad wire it is usually on top of the engine where it comes out of the ignition pin connector and branches out from there. I had one the other day they couldn't find and I told them to pull on each wire. Sure enough one was hanging on by a strand and came right out. Problem solved. look closely at each wire up there for any abrasion Check the two red wires that go into each ignition pin connector. You may still find a broken wire and it's camouflaged.

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The center panel that holds the ignition/starter switch in the cabin always comes in and out a lot. Every inspection, fuel filter replacement, and access to the tunnel. The switch tumbler rubs the instrument panel everytime the panel is removed and tugs at and chaffs the P lead wires going into it. I have seen a couple of cases where the P leads were broken, but at the switch instead of the ignition boxes. Give that a shot as well.

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I have seen a couple of cases where the P leads were broken, but at the switch instead of the ignition boxes. Give that a shot as well.

 

Broken P-leads would lead to ignition all the time on the module in question - not zero spark and no starting*.

 

The only thing that "defeats" an ignition module is to ground it.

 

Right?

 

 

*unless they were BOTH broken and BOTH grounded. Stranger things have happened, but kind of unlikely.

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OK. I disconnected the plugs to to the ignition modules and checked resistance in the wires. The red wires are grounded, and the white wires are open unless the ignition switch is at 1 or 2 or off. Nothing else seems frayed or loose.

 

My hangar may have been struck by lighting. Could that have an effect?

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Broken P-leads would lead to ignition all the time on the module in question - not zero spark and no starting*.

 

The only thing that "defeats" an ignition module is to ground it.

 

Right?

 

 

*unless they were BOTH broken and BOTH grounded. Stranger things have happened, but kind of unlikely.

 

Correct, I meant the wires on the tumbler where the P leads attach. There are about 8 wires or so on that tumbler that sometimes get broken causing havoc.

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You guys are awesome. When you figure this out, Optics, don't let it dampen your enthusiasm for OSH! Think of it. If you are at OSH and can't start, you have the largest collective brain on the planet, airplane-wise, to help you! WF

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OK. Today I dropped the bowl of the left carb. There was 1/4 tsp of water on the bottom of it, a dozen flakes of something, and water was dripping off the jets slowly as I watched. Clearly some water got into this side. I've been burning auto fuel for 5 years, never let it sit more than a few weeks, and have never had this problem. I should also mention that I have never seen any water when sumping the fuel pre-flight. I drained another quart of fuel and it was clean.

 

I had bought some fuel from a station east of Austin that made my Dynon read fuel flow strangely. I'll bet that was it.

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OK. Today I dropped the bowl of the left carb. There was 1/4 tsp of water on the bottom of it, a dozen flakes of something, and water was dripping off the jets slowly as I watched. Clearly some water got into this side. I've been burning auto fuel for 5 years, never let it sit more than a few weeks, and have never had this problem. I should also mention that I have never seen any water when sumping the fuel pre-flight. I drained another quart of fuel and it was clean.

 

I had bought some fuel from a station east of Austin that made my Dynon read fuel flow strangely. I'll bet that was it.

 

So, does your ct now start after this?

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If you ever visibly see standing water in 91 Oct with ethanol then you really need to drain all the fuel in the system. Normally the ethanol will absorb water and it burns right through the system and you may never know it. If you see any free water in a fuel system with 91 Oct with ethanol then that means you should consider all the fuel fully saturated. Drain it and start fresh.

If you don't have any ethanol in your fuel then you should see any water as it should separate out and be found at low points like the gascolator and carb bowls.

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I drained all 21 gallons (it will go into my POS Blazer which will burn anything). Sumped the remaining gas. Poured 2 gal of new stuff on each side (all my big gas cans were full), sumped it again, and pulled it out of the hangar. The engine started in half a turn of the prop. It has never done that before.

 

The left bowl had water, but the right one was clean. Either way, it should at least have sputtered or tried to run on 2 cylinders. I warmed up the oil and did a 3000 RPM mag check...within 10 RPM, 100 RPM drop as usual.

 

FWIW, the Lockwood guy said you couldn't see the spark from the plug unless you were in a completely dark room.

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If you ever visibly see standing water in 91 Oct with ethanol then you really need to drain all the fuel in the system. Normally the ethanol will absorb water and it burns right through the system and you may never know it. If you see any free water in a fuel system with 91 Oct with ethanol then that means you should consider all the fuel fully saturated. Drain it and start fresh.

If you don't have any ethanol in your fuel then you should see any water as it should separate out and be found at low points like the gascolator and carb bowls.

 

I'm not sure I understand this. Ethanol mixes with gasoline but mixes better with water. Water does not mix with gasoline. Since ethanol will separate from the fuel in order to mix with the water, how can the fuel be fully saturated if you see free water? I would think there would be three layers in your example. A layer of pure water on the bottom, a layer of phase separated ethano/water mix next and a layer of fuel on top.

 

 

There is not doubt that the fuel system should be purged, my confusion is on the question of the fuel being saturated with water if the ethanol has already phase separated.

 

 

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I bought some gas at a Texaco in Taylor, TX, while on a cross country. It was probably mixed with water. I flew with it right away so the water didn't have time to settle anywhere. The station I usually use gets a delivery every other day (12 pumps) and I've never had a problem with their (Exxon) gas.

 

It takes a lot of water to phase-separate E10 gas, but it is certainly possible that if you buy from a station that has the underground tanks ready for refill, you will get some water.

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Hi Jim,

 

 

Water does mix within the fuel in solution with the ethanol.

Depending on how much water you pour into 91 oct. with ethanol you won't see it. It stays in solution and distributed within the fuel mixed with the ethanol. This mix of fuel, ethanol and water will burn through your engine. Once the water is added above the ethanol's capacity to absorb it and keep it in solution the extra water layer you were talking about will form. If you poured a cup of water into one of your CT wing tanks full of 91 oct with 8%-10% ethanol you would never see it. If the fuel had 10% by volume of the ethanol it could hold quite a bit of water before it came out of solution. 100LL and 91 oct without ethanol can not do this and the water separates and sinks to the low points right away.

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OK. Today I dropped the bowl of the left carb. There was 1/4 tsp of water on the bottom of it...

 

Glad you found the issue - it's easy to get sidetracked down a blind alley.

 

Comments:

 

1) I wonder if we should all include a "float bowl check" at regular intervals. Monthly seems excessive, but every other month or quarterly?

 

2) I had an airhead BMW that wouldn't start one winter. Pulling the float bowl showed about 1/2" of ice (IIRC) holding up the float. Worth considering in below-freezing temps.

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