SUREFLY SIM4P Failure

[krw5927]

Haven’t replaced the fuse holder but I did change to the EarthX battery in April. Can’t imagine that would have anything to do with it, but the prop does spin noticeably faster when hot as opposed to cold. Could the SureFly mistake the engine already being at idle and no longer in start mode? Seems to me like it will only fire when the battery is nearly depleted as it did on Sunday. Just a hunch at this point. And the first SIM seemed fine with hot starts using the EarthX. Ill keep digging.

Could the SureFly mistake the engine already being at idle and no longer in start mode?

Interesting thought, you might be on to something. Someone else experienced a similar hot start problem in 2025 and this theory was proposed. Unfortunately the OP never posted about resolution:

However Surefly SIMs adjust timing during engine starts, it requires a change to my hot start procedure

I recently had to do a couple of hot starts with my dual SIM equipped IO-540. Having no luck with my normal methods I found that running the starter through 3-4 blades and then returning to the run position seemed to give me an easy, Instant start. At first I thought it was just luck but I’ve...

vansairforce.net

It seems a few folks believe the SureFly engages start-timing retard below 250RPM. Are you able to measure your hot-start RPM with an independent instrument? Confirming the retard cut-out RPM with SureFly would be a reasonable next step.

 

[lr172]

Interesting thought, you might be on to something. Someone else experienced a similar hot start problem in 2025 and this theory was proposed. Unfortunately the OP never posted about resolution:

However Surefly SIMs adjust timing during engine starts, it requires a change to my hot start procedure

I recently had to do a couple of hot starts with my dual SIM equipped IO-540. Having no luck with my normal methods I found that running the starter through 3-4 blades and then returning to the run position seemed to give me an easy, Instant start. At first I thought it was just luck but I’ve...

vansairforce.net

It seems a few folks believe the SureFly engages start-timing retard below 250RPM. Are you able to measure your hot-start RPM with an independent instrument? Confirming the retard cut-out RPM with SureFly would be a reasonable next step.

i can't see how heat alone could cause the retard on start to not work. it is just software. but could see how the whole unit fails when hot; components on board expand and can expose a weak solder joint. Also, starting without the retard actually makes it easier for the engine to start. we alone retard the advance to avoid kick backs, which can happen at the low rpms, due to limited inertia.

 

[lr172]

but the prop does spin noticeably faster when hot as opposed to cold. Could the SureFly mistake the engine already being at idle and no longer in start mode?

Certainly possible, but seems unlikely. Many folks have earthx batteries these days and can't see how the surefly folks could not have addressed that by now. early on, maybe, but not after 1000's of units in the field. it is just a rpm threshold that the software uses to decide whether the engine is cranking or running.

 

[krw5927]

i can't see how heat alone could cause the retard on start to not work. it is just software. but could see how the whole unit fails when hot; components on board expand and can expose a weak solder joint. Also, starting without the retard actually makes it easier for the engine to start. we alone retard the advance to avoid kick backs, which can happen at the low rpms, due to limited inertia.

My engine definitely turns over faster when the oil is warm vs the first start of the day. I'm not suggesting that heat impacts the retard. Rather the warm oil and components might allow a healthy starter and a really great battery to over-speed the retard limit of the SureFly.

The very same was suggested in post #14. You might even know the poster!

However Surefly SIMs adjust timing during engine starts, it requires a change to my hot start procedure

I recently had to do a couple of hot starts with my dual SIM equipped IO-540. Having no luck with my normal methods I found that running the starter through 3-4 blades and then returning to the run position seemed to give me an easy, Instant start. At first I thought it was just luck but I’ve...

vansairforce.net

 

[lr172]

My engine definitely turns over faster when the oil is warm vs the first start of the day. I'm not suggesting that heat impacts the retard. Rather the warm oil and components might allow a healthy starter and a really great battery to over-speed the retard limit of the SureFly.

The very same was suggested in this post

However Surefly SIMs adjust timing during engine starts, it requires a change to my hot start procedure

I recently had to do a couple of hot starts with my dual SIM equipped IO-540. Having no luck with my normal methods I found that running the starter through 3-4 blades and then returning to the run position seemed to give me an easy, Instant start. At first I thought it was just luck but I’ve...

vansairforce.net

i have to believe that surefly has figured out a reasonable threshold by now or there would be many complaints about kick backs during hot starts. Very easy to confirm. call surefly and ask them what the threshold is and observe your rpm while cranking. if it is happening, i think you would know bt now as kick backs would be fairly common for you.

my post in that thread was based upon a 250 rpm threshold that was suggested. no one in that thread ever confirmed that was the case and strongly doubt they set it that low. 400 is more common.

 

[paulsmeds]

Purchased an RV-6A with a Slick and ElectroAir working great. Then suddenly I had intermittent issues getting it started. 8 blade turns in or so it would finally fire one then another and start. Then run fine. Checked every connection, changed grounds, and then it worked great again. 4 months later the problem came back. I chose to pull it and replace with another brand.

When removing it, one of the last wires was the power lead to the control module going through a switch. To my dismay, the wire pulled right out of the connector. You could see where the crimp was bad and maybe had caught a strand of wire. When we thought every connection was checked, clearly we missed that one and it was the whole problem. Triple check every connection with a decent tug on the wire.

 

[eatonair]

Interesting thought, you might be on to something. Someone else experienced a similar hot start problem in 2025 and this theory was proposed. Unfortunately the OP never posted about resolution:

However Surefly SIMs adjust timing during engine starts, it requires a change to my hot start procedure

I recently had to do a couple of hot starts with my dual SIM equipped IO-540. Having no luck with my normal methods I found that running the starter through 3-4 blades and then returning to the run position seemed to give me an easy, Instant start. At first I thought it was just luck but I’ve...

vansairforce.net

It seems a few folks believe the SureFly engages start-timing retard below 250RPM. Are you able to measure your hot-start RPM with an independent instrument? Confirming the retard cut-out RPM with SureFly would be a reasonable next step.

That was my thought as well. Would be nice to know exactly how fast it was turning over. Unfortunately I don't know enough about internal circuitry to understand when the SIM switches from ATDC to 25deg BTDC. Maybe tech ops can shed some light.

 

[lr172]

That was my thought as well. Would be nice to know exactly how fast it was turning over. Unfortunately I don't know enough about internal circuitry to understand when the SIM switches from ATDC to 25deg BTDC. Maybe tech ops can shed some light.

If you call them, they should be able to tell you the threshold.

 

[eatonair]

Certainly possible, but seems unlikely. Many folks have earthx batteries these days and can't see how the surefly folks could not have addressed that by now. early on, maybe, but not after 1000's of units in the field. it is just a rpm threshold that the software uses to decide whether the engine is cranking or running.

Roger that. I'm just spitballin at this point. And my first SureFly was just fine with the EarthX.

 

[eatonair]

My engine definitely turns over faster when the oil is warm vs the first start of the day. I'm not suggesting that heat impacts the retard. Rather the warm oil and components might allow a healthy starter and a really great battery to over-speed the retard limit of the SureFly.

The very same was suggested in post #14. You might even know the poster!

However Surefly SIMs adjust timing during engine starts, it requires a change to my hot start procedure

I recently had to do a couple of hot starts with my dual SIM equipped IO-540. Having no luck with my normal methods I found that running the starter through 3-4 blades and then returning to the run position seemed to give me an easy, Instant start. At first I thought it was just luck but I’ve...

vansairforce.net

Hmmm, interesting. I'll try that procedure.