912iS engine roughness when cold

[rcarsey]

I've experienced this a few times already.. and it seems to happen when the OAT and/or oil temperature is below 50F...

Engine cranks normally, but when it catches, the engine will run very roughly for 1-5 seconds. I thought maybe one of the cylinders wasn't firing, but I see the all the EGTs rising while the roughness is happening.

Advancing the throttle seems to help clear it.. but without knowing whats causing it, I can't say if the throttle is actually helping.. or if it would have cleared itself up on its own. Another RV12iS owner reported similar behavior under 50F.

Here is a video (sorry the quality is crappy.. but I needed 3 hands to film it.). Hard to see, but the OAT is 47F; Oil Temp is 52F. Wh-ile its being rough, it looks like the gets up to 840rpm and all EGTs are between 180-200F. Oil PSI gets up to 4. Throttle position was initially set to 54%

https://www.youtube.com/shorts/e_cmUiLCqzo

Any ideas?

 

[dbhill916]

No ideas, but a data point -- I have the same behavior on a classic ULS engine.

 

[magiccarpet]

No ideas, but a data point -- I have the same behavior on a classic ULS engine.

Same here on another ULS 912. At low OAT the first few seconds after start-up the engine sounds quite rough. I have always considered that as normal and as expected. Not sure if that is really the case.

 

[G JWTP]

Hi Rob,

Couple of things.

How long do you have one or both fuel pumps running prior to start?
I generally wait for the ADHARS to align with one pump running to allow the system to clear any air and prime the injectors. ( I use clear air and prime injectors very loosely here). You should be able to hear the fuel gurgle back into the tank.

I set the throttle at 33%-35% as displayed on the EFIS. Don't touch the throttle during start. This should give you 2000RPM or their abouts once the engine has started. Start the engine. A healthy battery helps!!!!! Mine does sound like a bucket of bolts until it catches which only takes 1-2 seconds. Leave the throttle here for 1 minute to circulate the oil prior to increasing to 2500RPM for generator switchover. This works OK even down to 0C or 32F in old money.

I was on a recent course on the installation/operation/maintenance of 912iS engine with the UK agent. There were a few contentious issues where the following was explained.

1. There is a graph with the Installation booklet ( I think) that shows a throttle setting neccessary for various temperatures. The UK Rotax people think that starting a cold engine at 55% indicated on EFIS is not a good idea. Below 32F preheating is the way forwards. ( Open the oil door, poke in a hair dryer, go and have a cup of warming coffee/tea, Have a crack at starting it after 30 mins or so was their suggestion).

2. The coil packs are directly triggered from the ECUs. This may take 1-2 seconds to work it all out. Hence the roughness.

3. Letting the engine run for 60 seconds prior to increasing to 2500RPM for generator switchover is a good habit to get into and in real terms isn't much of a hassle.

4. Shutting down. Let the engine idle at 2000 RPM for a minute then as you close the throttle turn off the lanes. Turn B off fractionally before A. ( 1/10th second fractionally). This should give you a smoother shutdown, no-one seems to know, in the UK, exactly why.

Have a go and see how you get on.

Hope this helps,

John.

 

[henrysamson]

Could it be a transitory issue that only occurs when the soft start is active and clears when the soft start is deactivated? I am assuming here that the 912iS has the soft start.

I recently did the test flights on a RV-12 ULS and after about 5 -10 seconds the RPM would increase a couple of hundred RPM resulting in a smoother engine. The builder told me this was the soft start deactivating. My Kitfox with an older 912 ULS without the soft start does not have this issue.

Just a thought.

Henry

 

[rvbuilder2002]

Hi Rob,

Couple of things.

How long do you have one or both fuel pumps running prior to start?
I generally wait for the ADHARS to align with one pump running to allow the system to clear any air and prime the injectors. ( I use clear air and prime injectors very loosely here). You should be able to hear the fuel gurgle back into the tank.

I set the throttle at 33%-35% as displayed on the EFIS. Don't touch the throttle during start. This should give you 2000RPM or their abouts once the engine has started. Start the engine. A healthy battery helps!!!!! Mine does sound like a bucket of bolts until it catches which only takes 1-2 seconds. Leave the throttle here for 1 minute to circulate the oil prior to increasing to 2500RPM for generator switchover. This works OK even down to 0C or 32F in old money.

I was on a recent course on the installation/operation/maintenance of 912iS engine with the UK agent. There were a few contentious issues where the following was explained.

1. There is a graph with the Installation booklet ( I think) that shows a throttle setting neccessary for various temperatures. The UK Rotax people think that starting a cold engine at 55% power is not a good idea. Below 32F preheating is the way forwards. ( Open the oil door, poke in a hair dryer, go and have a cup of warming coffee/tea, Have a crack at starting it after 30 mins or so was their suggestion).

2. The coil packs are directly triggered from the ECUs. This may take 1-2 seconds to work it all out. Hence the roughness.

3. Letting the engine run for 60 seconds prior to increasing to 2500RPM for generator switchover is a good habit to get into and in real terms isn't much of a hassle.

4. Shutting down. Let the engine idle at 2000 RPM for a minute then as you close the throttle turn off the lanes. Turn B off fractionally before A. ( 1/10th second fractionally). This should give you a smoother shutdown, no-one seems to know, in the UK, exactly why.

Have a go and see how you get on.

Hope this helps,

John.

The throttle position indication has no correlation to percent power.
It is a throttle position value.
An indication of 50 is not a throttle position that will produce 50% power.
In colder temps, higher throttle position values (as detailed in the chart) are needed for good start performance.
I have seen poor start behavior in cold temperatures caused by auto fuel that wasn’t very old, but changing to fresh fuel resolved the issue.

I’m not clear on what the claimed benefit is from finning at 2000 for a minute befor initiating the power switchover.

 

[NORDO Industries LLC]

Same here on another ULS 912. At low OAT the first few seconds after start-up the engine sounds quite rough. I have always considered that as normal and as expected. Not sure if that is really the case.

This behavior is as-designed on the ULS, and I believe that the iS has similar behaviors. Low engine temps will always make things difficult for starting.

The ignition advances from being triggered by the leading edge of the coils to the trailing edge after several seconds in order to ease starting. That’s why you’ll start the engine and then a moment later it acts like it catches its breath and improves, even when starting an already-warm engine.

 

[Jayhox88]

I had this same issue twice on a recent trip. It only lasted 3-4 seconds, but it was certainly a "rough" start. As noted, temps were pretty cold in the mid 30's. Just another point of reference.

 

[rcarsey]

Well, my rough starts have continued intermittently this winter.. even on a warm 75F degree day here last week. Today, after 7 or 8 attempts at starting, I called it quits and just went home.

Today, it was a bit warm, 46F, and the engine was on a pre-heater as well. Throttle position was set to 65%, well into the green (shown in the attached chart from the 912iS Operations Manual). After a couple attempts, I decided to try running both fuel pumps (i normally start with only 1), starting with Lane A only.. starting with Lane B only.. nothing seemed to change the behavior. I finally broke out the camera to document two final attempts.. then I packed it in .. took my ball and went home.

This is really abnormal behavior.. as I haven't had this issue in prior years.. I have a dongle on the way to capture some data tomorrow.. even my hangar neighbor mentioned that he doesn't ever remember my engine not starting after 1/2 rotation.

 

[mikefox]

Rob,

It was good meeting you at OSH 2019.

In our club’s 12iS, we start at 45-50% throttle as indicated on the g3x. Fuel pump 1 is on and off for lights, strobes and avionics. As soon as the engine starts, I close the throttle smoothly to keep the RPMs below 2500. The engine starts rapidly.

Hope that helps.

 

[rcarsey]

So I did some testing today.. I _think_ I can finally put this one to bed (more testing needed, but promising). As it turns out, my start-up procedure seems to be at fault. I was releasing the ignition key as soon as the engine starts firing and it catches. However, the Rotax Operators Manual states that the starter should be engaged until you reach 1500 RPM. (The ULS manual has no such language) .

The engine fired up and was "rough" for less than 1 second.. during this time, the starter was still engaged and the dimming/flickering of the G3x screen indicated to me that the starter was still putting some effort into the engine to get it past the compression cycles.. as the frequency of the dimming increased to correspond with the engine rpm.

I'll likely be using this method from now on..since thats what Rotax has written. I'm unsure why I had never come across this in their docs before..

 

[NZ_Pompey]

So I did some testing today.. I _think_ I can finally put this one to bed (more testing needed, but promising). As it turns out, my start-up procedure seems to be at fault. I was releasing the ignition key as soon as the engine starts firing and it catches. However, the Rotax Operators Manual states that the starter should be engaged until you reach 1500 RPM. (The ULS manual has no such language) .

The engine fired up and was "rough" for less than 1 second.. during this time, the starter was still engaged and the dimming/flickering of the G3x screen indicated to me that the starter was still putting some effort into the engine to get it past the compression cycles.. as the frequency of the dimming increased to correspond with the engine rpm.

I'll likely be using this method from now on..since thats what Rotax has written. I'm unsure why I had never come across this in their docs before..

Hey Rob, I had the exact same starting experience with my iS in colder temps and ended up with the exact same remedy. Holding the key on for that extra second or 2 when the engine first caught ended up being the answer.

 

[FabricGATOR]

In our club’s 12iS, we start at 45-50% throttle as indicated on the g3x. Fuel pump 1 is on and off for lights, strobes and avionics. As soon as the engine starts, I close the throttle smoothly to keep the RPMs below 2500. The engine starts rapidly.

Hope that helps.

Remember guys, and I presume most of you already know, that the lower green arc for engine (and ground) operations is above 1800 RPM and preferred 2000.
Saves wear and tear on the gearbox, and your wallet.

Now I rig them to idle down as low as 1600 rpm if the installation will retain reliable engine operation in flight BUT that is only so the operator has the 'option' to remove some of the 'fly' energy out of the machine for landings. Ideally the operators should really learn how to land their craft without dropping below 1800 RPM's if at all possible.

Cheers

 

[mikefox]

Remember guys, and I presume most of you already know, that the lower green arc for engine (and ground) operations is above 1800 RPM and preferred 2000.
Saves wear and tear on the gearbox, and your wallet.

Now I rig them to idle down as low as 1600 rpm if the installation will retain reliable engine operation in flight BUT that is only so the operator has the 'option' to remove some of the 'fly' energy out of the machine for landings. Ideally the operators should really learn how to land their craft without dropping below 1800 RPM's if at all possible.

Cheers

Yes, our warm idle setting is 1800 RPMS.

 

[rvbuilder2002]

Remember guys, and I presume most of you already know, that the lower green arc for engine (and ground) operations is above 1800 RPM and preferred 2000.
Saves wear and tear on the gearbox, and your wallet.

Now I rig them to idle down as low as 1600 rpm if the installation will retain reliable engine operation in flight BUT that is only so the operator has the 'option' to remove some of the 'fly' energy out of the machine for landings. Ideally the operators should really learn how to land their craft without dropping below 1800 RPM's if at all possible.

Cheers

I can’t comment regarding other brands because I have no experience with them, but an RV-12 with the idle speed set at 1600 rpm will have an rpm that is at or above 1800 rpm during landing approach. Even at the lowest speed someone would use for a minimum distance short field landing.
It only goes lower right about the time the mains touch when near stall speed.
Once the nose is down, the throttle should be advanced to get the rpm back above 1800.

The difference in short landing performance between an idle of 1600 vs 1800 is pretty evident.