25 RPM fluctuations

[201Steve]

Take a look at video. ‘77 J. Cruise flight. Power and fuel settings appear to be no factor, but this was at WOT, 2500RPM, approx 40 LOP. 

[Oldguy]

You don't happen to have a recording engine monitor, do you? Comparing what it shows versus the display might be the first place to look.

[201Steve]

Also, here is engine monitor. 

[takair]

Almost looks like a problem with the tach.  Would check the harness and connectors first.  What’s going on with fuel pressure at the end of the clip?

[201Steve]

Good call on the fuel pressure. I had forgotten that had happened. Here is a full instrument scan where the fuel pressure is moving again. It didn’t seem to have a correlation but maybe another thing to keep an eye on 

[Guest]

In your first video, as well as fuel pressure the old Alcor EGT wanders almost in sync with the tachometer.

Clarence

[LANCECASPER]

23 minutes ago, 201Steve said:

Good call on the fuel pressure. I had forgotten that had happened. Here is a full instrument scan where the fuel pressure is moving again. It didn’t seem to have a correlation but maybe another thing to keep an eye on 

11566D6A-61C2-476E-964C-1F9485AAC222.MOV

Were your strobes on? If so, try it again with the strobes off just to see if there's a ground issue.

[201Steve]

29 minutes ago, LANCECASPER said:

Were your strobes on? If so, try it again with the strobes off just to see if there's a ground issue.

Yes. Strobe on. 

[carusoam]

Dial up the smartphone app... audio based tachometer... See if you can prove/disprove the ship’s gauge...

Do you hear anything changing?

PP thoughts, not a mechanic...

Best regards,

-a-

[201Steve]

On 12/27/2018 at 6:34 PM, M20Doc said:

In your first video, as well as fuel pressure the old Alcor EGT wanders almost in sync with the tachometer.

Clarence

All 3 seem to be goofing out a bit. Fuel Pressure, RPM, and Alcor EGT. The insight egt moves a little, but I figure there’s no way you get a constant EGT temp to the “T”. Or I wouldn’t think. 

[Guest]

I believe that your fuel pressure gauge is a mechanical gauge, so the pressure may indeed be wandering.  I don’t think it would affect EGT, the servo should be able to handle some variation in pressures.

 Your G1 engine monitor sadly doesn’t have data logging from what I read on Insight Avionics

The tachometer is electric driven by magneto impulses from the P lead circuit.  With a constant speed propeller, I don’t think the RPM would change unless the governor isn’t able to keep up.  Do you feel/ hear a change in engine performance?

Clarence

 

[201Steve]

On 12/29/2018 at 8:43 PM, M20Doc said:

I believe that your fuel pressure gauge is a mechanical gauge, so the pressure may indeed be wandering.  I don’t think it would affect EGT, the servo should be able to handle some variation in pressures.

 Your G1 engine monitor sadly doesn’t have data logging from what I read on Insight Avionics

The tachometer is electric driven by magneto impulses from the P lead circuit.  With a constant speed propeller, I don’t think the RPM would change unless the governor isn’t able to keep up.  Do you feel/ hear a change in engine performance?

Clarence

 

I’m hearing an occasional variation in sound/feel. It is maybe once or twice every 10-20 minutes. It’s very short, so by the time I start scanning and checking instruments, I can’t correlate it to fluctuation.  

[carusoam]

Well Steve,

That does sound unusual...

If I heard something that sounded like an uncommanded change in engine operation, my HR would start to increase...

Doing that every 10-20 minutes would lead to discomfort. 

Best regards,

-a-

[Rick Junkin]

40 LOP = low fuel flow. The fuel pressure fluctuation looks pretty smooth, so it probably wouldn't be fuel percolation, right? Does it behave the same if you run ROP?

Cheers,
Rick