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912iS slow start (cold weather only?)

S

subpar_bucker

Well Known Member
We are about half way through the flying portion of the PAP. No major squawks so far. One issue that I am seeing though is that the first engine start of the day is requiring extensive cranking (close to the 10 second limit) before the engine eventually fires up somewhat reluctantly. It may then immediately come up to 2000 rpm, or sometimes it runs quite rough for a few seconds before finally running normally. I do not recall this issue when the weather was warmer (FYI, I'm located just north of Pittsburgh PA here in the USA).

We pulled two spark plugs (top and bottom) the other day and they looked great. I pulled the G3X logs from the test flights so far and there are no errors listed there. Nothing on the G3X during flight, so this seems like a start up issue. One of my mechanic friends said, "if this were a 78 Buick pumping the gas would get it to fire right up." Which I thought was quite funny.

I will try to make a video of it today and will call Van's support on Monday. I believe I was in the very first batch of 912iS engines Van's shipped to 12iS builders. There's no adjustable idle screw on my throttle intake. I can get the serial number if that's helpful.

One guess was there's a sensor somewhere that's not detecting the change in temperature and varying the mixture appropriately.

Any help appreciated. I searched the forums but didn't see anything that matched this issue.

-bob

PS, the engine runs great otherwise. If anything, we've been impressed by how little fuel we've gone through so far!!
 
Can you provide before start oil temp, throttle setting, battery voltage and fuel pressure?
 
jrtens said:
Can you provide before start oil temp, throttle setting, battery voltage and fuel pressure?
Click to expand...

And are you still using summer blend auto fuel?
I have seen it or using old fuel, cause the exact symptoms you are describing.
A simple test would be to add some 100 LL and see if the starting performance significantly changes.
 
jrtens said:
Can you provide before start oil temp, throttle setting, battery voltage and fuel pressure?
Click to expand...

And are you still using summer blend auto fuel?
I have seen it or using old fuel, cause the exact symptoms you are describing.
A simple test would be to add some 100 LL and see if the starting performance significantly changes.
The percent throttle value you use during start needs to be varied depending on 0AT. Up to 50% can be needed depending on the temperature. 35% is about right for warm temperatures.
 
Here's the video of today's first start, hopefully there's enough data and audio to help diagnose the issue:

https://youtu.be/nGu0HDQ1Yhw

Eventually youtube will convert that to a 4k video. After that happens, you can zoom into individual frames to double check my data if you'd like.

The OAT today was 53F. We did preheat the oil for about an hour prior to starting (I have the Reiff preheater installed). Looks like the oil temp was 73F at start up. The throttle was set at 48%. Fuel pressure is 45.6 PSI and battery looks like 13.1V. We've seen the same issue with a freshly charged battery prior FYI.

To Scott's question, we've only run 100LL in the engine so far. Maybe about 10 gallons so far.

We were adjusting the idle RPM today. I cannot recall exactly how many times we started the engine (maybe 5 times). The first start is the only time I see this. The engine fires normally every time thereafter.
 
The ECU needs 700 rpm to initiate start and it looks like you are having a hard time getting there.

You see in the video once you get to 700 it starts right up.

Three possibilities are battery, starter and sprag clutch. Whatever it is works better when it's warm apparently.

It is possible for the battery to lose cranking power even though it shows good voltage.

One other thing I noticed is after start, the rpm went over 2500 so I assume the generator switch took place but the voltage was 11.7 when I would expect to see 13.8 to 14.

Perhaps the switchover did not occur since the rpm was only up momentarily but the battery amps went to +15 which seems to indicate charging.
 
Last edited:
I think my vote is for clogged up fuel injectors in Cyl 1 & 3 -- since the EGT temps on those cylinders seems to be lagging behind 2 & 4.

Here's a still of just after the EGTs start to rise.. note Cyl 1 is still at 60.

The starter cranks at approx 200 rpm.. so at this point, the engine is running faster than the starter can.. so I think the starter is OK.
 

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I appreciate the input, Scott, Jon and Rob. Today of course the engine started immediately (and we had frost on our roof this morning). I'll call Lockwood support tomorrow afternoon. I will report back the eventual solution whenever I have a conclusion.
 
Jon,

I realized I never addressed this question:

>One other thing I noticed is after start, the rpm went over 2500 so I assume the generator switch took place but the voltage was 11.7 when I would expect to see 13.8 to 14.

The switchover did happen, but it's very quick. Watch the battery amps around 14 seconds into the video. You can see the white chevron raise up above the red bar. After that happens, Volts goes to 13.7, Alt Amps rises above 20 and the Batt Amps goes to +17.

This confused the guys doing my PAP the first time they saw it. I think that maybe it would be helpful to have a green bar above the red bar displayed for Batt Amps.
 
Just a quick update on this thread. A few days ago I left the oil heater plugged in over night with a blanket over the cowl and the next morning the engine fired up immediately.

This after noon (with no preheating) the engine again cranked for several seconds before firing. I have a new earthx battery on the way. I'll report back on that once it has been installed.
 
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