2008 Turbo Normalized - Experience with High Boost run-up and ALT 1

Hi everyone!

This is my first post. I’ve been flying Cirrus SR22’s for the most part for the past 13 years. I thought I would post my experience today to share and see if anyone can offer me any insight.

I went out to fly today at my home field of KVNY (Van Nuys, CA) in a 2008 SR-22TN. Started up, got my TEC clearance and went to runway 16R to do a run-up. Upon beginning my before takeoff checklist I immediately noticed the engine wasn’t running quite right. Just a little rough or maybe a plug issue. That wouldn’t be the first time that’s happened on the Cirrus. Total time between startup and run-up was probably 10 minutes max. The weather was pretty nice today, don’t know if that’s a factor in what I’m about to describe but it was about 75 degrees.

So before going through the entire checklist I thought let me see if this is a plug issue and see if I can clear it. I pulled back the mixture a little less than 2/3 of full and ran the engine up to about 2200 rpm and kept it there for about a minute. Immediately after that I reduced power to 1000 rpm and noticed it was running rough still. Did it again for a minute and same result. The A/C was running. Upon completing the second round of attempting to clear the plug of potential crud I immediately noticed the ALT 1 went yellow. On the engine page it was producing 0 to +1 charge. Power went up to 1700 just to make sure it wasn’t a low engine rpm issue. The warning was still there and wouldn’t go away. I initially thought there is a short or some issue with ALT 1 altogether. Instinctively I thought let me turn off the A/C (set the fan to zero) so the fan and compressor go off. As soon as I did that the ALT 1 came alive, the flashing yellow warning disappeared and was producing normal charge. I was able to reproduce the issue with ALT 1 but turning the A/C back on.

I did a run-up again and the engine was still running rough. Both my flight instructor and I didn’t realize until taxi back to the ramp and shutdown that the pump was on high boost. We had already decided not to fly at that point and still believed there was an issue based on what I explained above with ALT 1.

If you’re wondering if I cycled the L/R mags, I never got to the point.

I left for the day and my instructor called me back within 30 minutes and said he went out again and ran the engine up on low-boost and it ran perfectly. Also he couldn’t at that point replicate the ALT 1 warning issue. I didn’t ask him if he turned the pump to HIGH-BOOST to see if it the ALT 1 warning could be replicated but I’m going to try before I go flying again on Saturday.

What’s left me scratching my head is why did the ALT 1 seem to be an issue during all this and then when my flight instructor later did a run-up with the pump on LOW-BOOST the ALT 1 warning no longer appeared.

I’m curious if any of you have experienced this or have any insights as to what you think it may have been with regard to the ALT 1 and HIGH BOOST.



High boost can definitely provide too much fuel

Alt 1 and A/C at moderate to low rpm can discharge the battery.

Did you note voltages or take a photo/video?

High boost on a TN can cause rough running as the mixture is overly rich.

It appears to me you were focused on the alternator (distracted) and the real issue all along was inadvertent high boost selection and subsequent mixture adjustments.

The voltage issue resolved itself with enough rpm to produce power to the avionics and environmental system.

Don’t take this the wrong way, but it sounds like you need some review of your ground procedures. As was mentioned, high boost on a turbo is way too much fuel for anything but priming on the ground. And it also sounds like you taxi with the mixture full rich by your description of when you leaned to clean up your potential bad plug. That’s another no no. Lean brutally on the ground. All the way back until the engine almost stumbles. Do a quick search about why. This will keep your plugs clean also. I’d get with your instructor and go over all of this.