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SUREFLY SIM4P Failure

eatonair said:
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.
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eatonair said:
Could the SureFly mistake the engine already being at idle and no longer in start mode?
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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.
 
krw5927 said:
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.
Click to expand...
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.
 
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?
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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.
 
lr172 said:
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.
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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
 
krw5927 said:
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
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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.
 
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.
 
krw5927 said:
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.
Click to expand...
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.
 
eatonair said:
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.
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If you call them, they should be able to tell you the threshold.
 
lr172 said:
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.
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Roger that. I'm just spitballin at this point. And my first SureFly was just fine with the EarthX.
 
krw5927 said:
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
Click to expand...
Hmmm, interesting. I'll try that procedure.
 
lr172 said:
If you call them, they should be able to tell you the threshold.
Click to expand...

Just spoke with Matt again at SureFly. Start mode is confirmed to be TDC at less than 400 rpm @ 60mj. DIP switch setting above 400 rpm @ 45mj.
I thought it odd (and I did inquire) that SF has no customer bulletins, advisories or service bulletins, for any SIM. I know SureFly is a great product, but NO bulletins?
I did find one on the Lycoming website pertaining to some helicopter engines.
 
paulsmeds said:
Triple check every connection with a decent tug on the wire.
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Good advice. The late great Bob Nuckolls suggested you should be able to hang a gallon milk jug on the wire without it coming out, in case you are wondering what a "decent tug" is.
 
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eatonair said:
Just spoke with Matt again at SureFly. Start mode is confirmed to be TDC at less than 400 rpm @ 60mj. DIP switch setting above 400 rpm @ 45mj.
I thought it odd (and I did inquire) that SF has no customer bulletins, advisories or service bulletins, for any SIM. I know SureFly is a great product, but NO bulletins?
I did find one on the Lycoming website pertaining to some helicopter engines.
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i don't think any battery starter combo is goiing to spin that engine over 400 regardless of temp.
 
lr172 said:
i don't think any battery starter combo is goiing to spin that engine over 400 regardless of temp.
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Correct -

And perchance the SIM were to switch between timing modes while the starter was engaged there likely be would be one heck of a kickback...the gnashing of teeth, starter nose case in pieces, etc. etc.
 
Ok, here we go.
After more testing this week, more frustration and head scratching. Rechecked everything again! Even modified my starting technique to the point that I could occasionally get the engine to start while hot but it wasn’t a happy start at all, and wasn’t consistent. Still felt there is something wrong with this second SIM.

Yesterday decided to pull the SIM. Went through my Slick mag by pulling the coupling, inspecting the rotor, condenser, coil and changing the points. E-gap set, installed and timed both Slicks. As expected the engine starts easily when cold. What I didn’t expect was that the engine now starts better than it has ever started with an impulse coupled mag while HOT! Starts like it first did years ago with the SIM! Go figure.
My guess is the faster cranking with the EarthX really helps with an impulse coupling. Especially while hot.

So something is definitely not right with this second SureFly. Got a return authorization and will ship it back Monday. Have no idea what testing will reveal because tech support admitted that bench checks don’t involve heating the SIM. In the mean time I’ll concentrate on getting ready for Oshkosh using two Slicks instead of screwing around with the SureFly. At least now I know I’m not losing my mind and have some confidence back.
Will keep you posted on the test results, I’m certain SureFly will make it right. However, not sure if and when I’ll get around to reinstalling the SIM.
Fly safe all! Ray
 
eatonair said:
Do you have the ability to start with both SIMs hot. Or do you operate with a key switch combo that defeats the right mag? Would be nice to be able to start on both.
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I have individual mag switches. I always start with both hot. I do not use a key switch. I have not experimented starting with one SIM but wondered if I should try. I'll keep using both for now,

Truth is we have data that says our SIM's are failing to provide a properly timed confident spark during start. And data says a very popular battery might be the a common theme to explore but I want more data on this idea.

I am going to start a new thread on the topic of SIM & hot starts, kickback, and EarthX in a few minutes. Your original issue was a very different issue than Hot Starts. I sent a message yesterday to Surefly with links to this thread and another thread. I want to partner with them and help them understand what the industry is experiencing.

We can help discover the issue and the fix. Swapping to another product is not in Surefly's best interest and leave is unresolved. SIM Giving us all a confident, well timed spark during start is achievable. Maybe it is. But maybe not....So tell me why kickback is an issue....
 
eatonair said:
Ok, here we go.
After more testing this week, more frustration and head scratching. Rechecked everything again! Even modified my starting technique to the point that I could occasionally get the engine to start while hot but it wasn’t a happy start at all, and wasn’t consistent. Still felt there is something wrong with this second SIM.

Yesterday decided to pull the SIM. Went through my Slick mag by pulling the coupling, inspecting the rotor, condenser, coil and changing the points. E-gap set, installed and timed both Slicks. As expected the engine starts easily when cold. What I didn’t expect was that the engine now starts better than it has ever started with an impulse coupled mag while HOT! Starts like it first did years ago with the SIM! Go figure.
My guess is the faster cranking with the EarthX really helps with an impulse coupling. Especially while hot.

So something is definitely not right with this second SureFly. Got a return authorization and will ship it back Monday. Have no idea what testing will reveal because tech support admitted that bench checks don’t involve heating the SIM. In the mean time I’ll concentrate on getting ready for Oshkosh using two Slicks instead of screwing around with the SureFly. At least now I know I’m not losing my mind and have some confidence back.
Will keep you posted on the test results, I’m certain SureFly will make it right. However, not sure if and when I’ll get around to reinstalling the SIM.
Fly safe all! Ray
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THATS great Data! I love data! Will you copy and paste this onto the new thread?

Surefly SIM, Hot Starts, & Kick back

Service Difficulty: My Lycoming IO-360 is very difficult to hot start and (rarely) has kickback during start despite taking precautions to avoid this. My Goal: The SIM delivery of confident Spark every time every cylinder reaches TDC on the start’s compression stroke. Eliminate all...
vansairforce.net
 
Bcone1381 said:
I have individual mag switches. I always start with both hot. I do not use a key switch. I have not experimented starting with one SIM but wondered if I should try. I'll keep using both for now,

Truth is we have data that says our SIM's are failing to provide a properly timed confident spark during start. And data says a very popular battery might be the a common theme to explore but I want more data on this idea.

I am going to start a new thread on the topic of SIM & hot starts, kickback, and EarthX in a few minutes. Your original issue was a very different issue than Hot Starts. I sent a message yesterday to Surefly with links to this thread and another thread. I want to partner with them and help them understand what the industry is experiencing.

We can help discover the issue and the fix. Swapping to another product is not in Surefly's best interest and leave is unresolved. SIM Giving us all a confident, well timed spark during start is achievable. Maybe it is. But maybe not....So tell me why kickback is an issue....
Click to expand...
for you and eaton, I would definately consider testing with a timing light on a plug to observe presence of spark. A big step forward here would be understanding whether this ia a no spark situation, possibly intermittent through the cranking phase, or improper advance/timing issue. Seems clear in your two cases that heat is the variable, but can't put it on the surefly yet without more data. No spark could point to something outside their box, like power input, grounding, plugs and their wires, etc. it would also point the SF guys in the right direction.
 
Bcone1381 said:
I have individual mag switches. I always start with both hot. I do not use a key switch. I have not experimented starting with one SIM but wondered if I should try. I'll keep using both for now,

Truth is we have data that says our SIM's are failing to provide a properly timed confident spark during start. And data says a very popular battery might be the a common theme to explore but I want more data on this idea.

I am going to start a new thread on the topic of SIM & hot starts, kickback, and EarthX in a few minutes. Your original issue was a very different issue than Hot Starts. I sent a message yesterday to Surefly with links to this thread and another thread. I want to partner with them and help them understand what the industry is experiencing.

We can help discover the issue and the fix. Swapping to another product is not in Surefly's best interest and leave is unresolved. SIM Giving us all a confident, well timed spark during start is achievable. Maybe it is. But maybe not....So tell me why kickback is an issue....
Click to expand...
That boggles my mind, you have both SIMs firing during a hot start and neither will produce reliable combustion.
What the heck is going on there. I was beginning to think my situation was somewhat unique.
I’m using individual mag switches as well but my installation is obviously different from yours. Your problem is literally twice as frustrating as mine. Wish I had more useful data to share with you.
I can tell you that the temperature of the mags as measured with an IR thermometer during hot starts was 165-170 deg F. Airflow around the accessories section during flight was measured at 150 deg F using thermocouple. ( although that temp might be skewed by cooling ducts and will require additional testing)
 
eatonair said:
That boggles my mind, you have both SIMs firing during a hot start and neither will produce reliable combustion.
What the heck is going on there. I was beginning to think my situation was somewhat unique.
I’m using individual mag switches as well but my installation is obviously different from yours. Your problem is literally twice as frustrating as mine. Wish I had more useful data to share with you.
I can tell you that the temperature of the mags as measured with an IR thermometer during hot starts was 165-170 deg F. Airflow around the accessories section during flight was measured at 150 deg F using thermocouple. ( although that temp might be skewed by cooling ducts and will require additional testing)
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Today I got it good and hot (oil temp & CHT) doing pattern work, then returned for some testing. My Cowl Temp peaks 15 minutes after shutdown. The base of the SIM was 178F with a thermocouple probe at its base, and 162F near the ignition harness cap. I performed starts leaving one SIM off, and I learned that it will kickback starting on each individual L and R mag.

Do you use Auto Plugs? I do and wonder if they might play a roll.

I will use a timing light tomorrow I hope and see if I can watch the timing action of both a cold engine and a hot one. Also looking for a Lead ACid battery to try. I cant imagine its related to the EarthX but its an easy variable to test.
 
Bcone1381 said:
Today I got it good and hot (oil temp & CHT) doing pattern work, then returned for some testing. My Cowl Temp peaks 15 minutes after shutdown. The base of the SIM was 178F with a thermocouple probe at its base, and 162F near the ignition harness cap. I performed starts leaving one SIM off, and I learned that it will kickback starting on each individual L and R mag.

Do you use Auto Plugs? I do and wonder if they might play a roll.

I will use a timing light tomorrow I hope and see if I can watch the timing action of both a cold engine and a hot one. Also looking for a Lead ACid battery to try. I cant imagine its related to the EarthX but its an easy variable to test.
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Type of plug should be irrelevant, though an excessive gap could be an issue. Coils sometimes output less power when hot and a large gap could cause it to not spark.. The kickback implies the possibility of not retarding the ignition. The timing light will tell the tale, but may also want to investigate the possibility that you are getting over 400 rpm when hot. Doesn’t seem likely but worth looking into. Also possible the sim is advancing above something below 400.
 
Bcone1381 said:
Today I got it good and hot (oil temp & CHT) doing pattern work, then returned for some testing. My Cowl Temp peaks 15 minutes after shutdown. The base of the SIM was 178F with a thermocouple probe at its base, and 162F near the ignition harness cap. I performed starts leaving one SIM off, and I learned that it will kickback starting on each individual L and R mag.

Do you use Auto Plugs? I do and wonder if they might play a roll.

I will use a timing light tomorrow I hope and see if I can watch the timing action of both a cold engine and a hot one. Also looking for a Lead ACid battery to try. I cant imagine its related to the EarthX but its an easy variable to test.
Click to expand...
Almost exactly the same temps I saw in my testing. Seems like I would get an occasional kickback from my single SIM but it was very weak? Nothing that would damage the starter, just kinda stops the prop. Really unpredictable!
And I am using the massive electrode plugs with champion wires.
 
lr172 said:
Type of plug should be irrelevant, though an excessive gap could be an issue. Coils sometimes output less power when hot and a large gap could cause it to not spark.. The kickback implies the possibility of not retarding the ignition. The timing light will tell the tale, but may also want to investigate the possibility that you are getting over 400 rpm when hot. Doesn’t seem likely but worth looking into. Also possible the sim is advancing above something below 400.
Click to expand...
My plugs are new and gapped iaw Surefly instructions for Autoplugs. Thats more than aviation plugs. maybe .028 - .032? Regarding RPM during start. I watched for that yesterday. The CGR-30P records 0 RPM during start, so I dont't have a numerical datapoint. But I established an intentional datapoint "feeling" about RPM but doing cold starts, then hot starts with no ignition, then hot starts with just one SIM firing. I feel like as the start progressed slight slowdown of the RPM tool place indicating possibly a pre-TDC spaark event too weak to kickback. Timing light will be revealing.
 
Bcone1381 said:
My plugs are new and gapped iaw Surefly instructions for Autoplugs. Thats more than aviation plugs. maybe .028 - .032? Regarding RPM during start. I watched for that yesterday. The CGR-30P records 0 RPM during start, so I dont't have a numerical datapoint. But I established an intentional datapoint "feeling" about RPM but doing cold starts, then hot starts with no ignition, then hot starts with just one SIM firing. I feel like as the start progressed slight slowdown of the RPM tool place indicating possibly a pre-TDC spaark event too weak to kickback. Timing light will be revealing.
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Not sure i fully understood your last point, but sounded like you said the rpms slowed sown progressively with ign on vs off. If the ign was firing at tdc or some point ATDC, you should not experience that. The fact that you did, possibly indicates the sim is advancing. but without any signs of the engine attempting to start, this could also be something related to the power system. A solid firing event occurring 25* btdc, that kicks off combustion is likely to create a kick back or at least create a major slow down and possibly a reversal of the prop. Now if it were say 5-10 btdc, that may be different. But usually a successfull firing event will be noticed by the operator, even if the engine doesn't start. just one or two combustion events is all it really takes to get the engine spinning and start coughing and choking. just ask anyone that almost tore their arm off rotating a prop around with the ign on or hand propped a plane.
 
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