Found broken start ring cogs

[David-aviator]

Am doing condition inspection and have had to replace the start ring on fly wheel due to 4 broken gear cogs.

The issue is kick back from electronic ignition on start. In talking with Robert Paisley, this is happening because I do not have back up 12 volts for the system. Voltage drops during start and EI looses its brain and fires way off schedule.

I stopped using EI for start some time ago when this happened repeatedly. It does not happen starting with left impulse coupled mag. I have mag hooked up to top plugs so it starts very easily. When engine is running smoothly, turn on EI. No big deal.

It is not a starter issue, am using Sky-Tec NL unit, it spins engine very nicely and its gear cogs are like new.

[rv6ejguy]

Unlikely battery voltage is dropping too low as the CPU will run down below 7.5V. Doubtful the starter will crank the engine if the voltage is dropping that low.

You could check to see if the CPU reset due to interference or low voltage by putting the display in gauge mode first, then cranking. If it stays in gauge mode the CPU did not reset. If it goes back to the bootup screen, it's either resetting or losing power/ ground. If the CPU cannot execute all the code, it will auto reset which takes about 0.5 seconds.

I suspect possible interference with the Hall sensor signal, possibly from close proximity to the starter cable which may be inducing a voltage exceeding logic level in the cable.

Do not share ECU grounds with any other terminal/ device. Do not share power from any other terminal, especially coil power or anything that has high voltage/ amperage or pulsing current on it.

Don't tie the CPU and ECU driver grounds together.

[DanH]

Observed ECU brownout on the Barrett dyno, first start attempt of John Walker's 540. Another battery was wired separately to drive the EFII system.

[Andrew Anunson]

Originally Posted by David-aviator

The issue is kick back from electronic ignition on start. In talking with Robert Paisley, this is happening because I do not have back up 12 volts for the system. Voltage drops during start and EI looses its brain and fires way off schedule.

Do the installation instructions require the installation of a back up battery for starting? Some here like to start the engine on the EI, since their backup ignition is a non-impulse magneto. If the flyefii ignition requires a complete backup battery system just for starting... well this sounds like a non-starter to me.

[rv6ejguy]

Decent battery/ cable setups should be able to maintain 9 volts when cranking the engine. If not, you should look there first. The controller will work down below 7.5V.

When the engine cranks slowly, the pistons slow noticeably coming up on compression, which effectively advances timing. This can cause a kickback.

Default retard when cranking is 15 degrees. Default timing for cranking is 10 degrees so actual timing when cranking with a good starter battery setup should be around 5 degrees ATDC. If you have V27 or later software, cranking retard is user programmable.

EFII uses the SDS ECU. 500,000+ flight hours, 25 million ground hours, many thousands in service for over 20 years. I've personally got collectively over 10,000 hours on the system in cars and aircraft. I've started our cold soaked shop car down at -34C with this system where it barely turned over. No kickback. You shouldn't need a separate battery to start the engine unless you have some wonky wiring or a poor battery/cable setup.

[David-aviator]

Originally Posted by Andrew Anunson

Do the installation instructions require the installation of a back up battery for starting? Some here like to start the engine on the EI, since their backup ignition is a non-impulse magneto. If the flyefii ignition requires a complete backup battery system just for starting... well this sounds like a non-starter to me.

With single EI and mag, backup power is not required.

But there is an issue of power available for EI during start without BU power, it is true of all EI systems. I had Electoraire years ago, it too broke start ring. On some starts all is well, others it is not. I believe my system would not reset to TDC if engine spun up and then quit due to inadequate priming.

Does the engine start better using EI, of course it does, there is more voltage to plugs. But starting on mag is a non issue, we've been doing it for over 75 years. I have no problem with it, hot or cold engine. Deliberately have mag hooked to top plugs. Net result is have a 20 rpm drop with both systems during mag check. EI is stuck with bottom plugs, it all evens out.

The Robert Paisley EI system is good, go with it if you are inclined to do high altitude flying. If most flying is below 8000', it does not matter than much. I went with single EI because no back up power required and I believe it provides about 95% of what you get with dual EI.

[erich weaver]

Originally Posted by David-aviator

But there is an issue of power available for EI during start without BU power, it is true of all EI systems.

This isn't true. Pmags for one work well down to the 9 volt range. If your voltage is dropping this low during start, your battery is shot or something is wrong in the wiring. There are large numbers of us flying on electronic ignition with no backup battery and no starting problems.

Erich

[Toobuilder]

Originally Posted by David-aviator

...But there is an issue of power available for EI during start without BU power, it is true of all EI systems...

This is a bold and absolute statement. As such, it requires some further exploration.

I've used dual Pmags on two airplanes and dual CPI on the latest and have never had any form of back up, starter boost, auxiliary battery, etc, and I have never experienced a brownout, lost timing or kickback event. Both the Pmags and SDS CPI will fire the plugs at voltages far below that which will turn the engine over. So if your engine spins over "very nicely", then you do not have a EI issue, you likely have a wiring issue. And as wiring issues (specifically bad grounds) are so very common in equipment problems, I'd look hard at your particular architecture and execution to see if things are up to snuff.

Bottom line is that a single EI on a 4 banger pulls about 1 amp at maximum RPM, and will fire at very low voltage. There should be no need for any form of electrical "boost" during start. After all, cars don't run dual batteries to keep the ignition alive during the start event.

[rv6ejguy]

Originally Posted by BillL

The way (angle) that the engine stops is always the same. That means the first FULL compression stroke is the second cylinder to compress on the 6, after that the speed (inertia) yields lower RPM variation.

The 4 cylinder only fires twice a revolution and has high torque demand on the starter each compression stroke as there is no overlap of an expansion stroke from another cylinder. This means the RPM variation is greater on the 4 than the 6 though a revolution.

It should be noted that the 4 cylinder torque requirement on the second compression stroke it is higher than the 6 which gets some help from other cylinders. What might work on the 6 might not work on the 4.

The ECU establishes the time interval between magnet/Hall sensor passage for one complete crank revolution before initiating any spark events. The system is vastly proven with literally millions of starts on 4 cylinder engines.

[rcpaisley]

This is one of the benefits of the Bus Manager - protect the 12v supply to the ECUs during starting.

If an existing install develops this issue, it is usually a battery getting weak.
If an original installation with a fresh battery has this issue, it could be voltage drops in the starter power wiring. Grounding wire layout issues are VERY common
in experimental aircraft.

In any case, it is typically a voltage droop issue during cranking that causes this,

Robert