fluctuating rpm / map
 

Hi.I have a new titan io370 with dual pmags, c/s prop and afp150 vertical induction fuel injection system. It runs fine apart from at 1150rpm when the rpm fluctuates between 1100-1200. Also when running at 2300rpm the map fluctuates by about 1". All other rpm settings seem stable in rpm and map. I'm guessing that at 2300 the governor is maintaining the rpm. Not sure if its a weird resonance or something else is going on. The engine is brand new and has around 4 hours flight time on the aircraft. Has anyone else experienced this issue and how did you solve it?
Thanks

The governor will not maintain 2300 rpm un less you set it to 2300rpm. If it is set for take off RPM then it will not kick in until you reach that RPM. So it is unlikely that the rpm is being maintained by the governor at 2300rpm.
What type of indications are u seeing? Electronically generated or steam gauges generated? can you hear the rpm change at 1150 or do you just see it on the tach?
Merry Christmas,
Mahlon

Does the EGT rise when the MP wanders at idle? According to Vic, (great webinar Vic!) you may have an intake leak. Just a thought.

-Marc

Do you have restrictors in your manifold pressure lines?

If not, the P-mag timing could be bouncing around, causing the fluctuations.

There is a restrictor in the manifold pressure line, I believe as supplied by Vans so i dont know if its small enough. It only fluctuates at 11-1200rpm and you can hear it change. From the garmin pilot app I can see that as the rpm decreases the map increases.
During flight when we set the rpm to 2300 its stable but the map fluctuates.
I haven't noticed the egt following any pattern.
The instrumentation is all garmin g3x.
Is it possible that there is something resonating at those frequencies?
Miller

Miller,

Download the engine data and upload it to Savvy Analysis for review. Allow the data to be shared and post a link here.

You have 4 hours on this engine and you are already flying at 2300 RPM? Was it broken in on a test stand?

Yes, the break-in was done by titan.

have you tried adjusting the mixture leaner, when it is doing it, to see if that will change anything?
Good Luck,
Mahlon

Hmmm...
 

On MAP irregularities: I know Van's provides "restricted" AN fittings for the Oil Pressure and Fuel Pressure -- didn't know about the MAP.

If you are using the parts that came in the IE VMP install kit, those are not sufficient to damp out the pulses seen in the MAP when connected to the #3 intake port.

You will need OMEGA Engineering Snubber or similar damping between the #3 intake port and the MAP sender (https://www.omega.com/en-us/sensors-.../p/PS-SNUBBERS). Or, drill/tap another hole in the intake manifold and use that for the MAP source.

On RPM: How is the RPM being sensed? Mechanical tach/sensor to EFIS, or Ignition Box output to EFIS? I would obtain an optical tachometer (see omega engineering or sporty's or AC Spruce) and verify the numbers before doing anything else.

Good luck!

B