914T Engine Balking Issue

[grantopperman]

Hi All:

I'm wondering if anyone has experienced an engine issue similar to one I had today. 

When I powered up for the take off run, the engine momentarily balked and lost power every time it approached 4000rpm. Smooth acceleration until that point, then an abrupt loss of power for maybe ½ second at about 4000rpm. Then, power comes back, begins to spool up again and does the same thing. The best way I can describe it is that it feels like someone pushing in the clutch pedal on a manual transmission car for just a second. 

After I aborted takeoff, I was able to replicate the issue in the run-up area with the plane motionless. Smooth power up to 4000 and then the "clutch" moment and back to powering up again.

Some background: I had the circlips AD and an oil change performed about six weeks ago and flew the plane home with no issues. This is the first time I have tried to fly since then. Preflight run-up was normal. Postflight inspection of the engine didn't show any leaks or other anomalies. My aircraft is a 2017 P2008 with 914 turbo engine and 270 hours TT.

Any ideas what may be causing this and how I can troubleshoot the issue? Thanks for any thoughts.



Grant

[Ed Midgley]

I would open the gascolator to make sure it’s not a fuel flow problem. I tried to take off once with the fuel pump breaker pulled. It ran fine until take off power was applied. After about a hundred yards it fell back to idle.
Ed

[Glenn]

You haven't said what your indicated fuel pressure was during these episodes.  

[grantopperman]

Thanks for the initial thoughts! I didn't note the fuel pressure in the moment. I do know for sure that the fuel pump breaker was not pulled and the aux pump was on.

Mark Gregor suggested the possibility of a turbo waste gate issue in addition to the fuel ideas noted above. I'll go back out to the airport in the next few days, try another full power runup at Mark's recommendation (40 in for 3-4 mins) and report back along with noting the fuel pressure.

[montanapilot]

Every one of these cases seems to be a bit unique. My problem was that I would lose some power during climbout. I'd reduce the throttle and it would run smoothly. If I added power again, I'd have a power loss. My problem turned out to be the carb bowls not seating properly. I sent them to Lockwood and no problem after that. Again, I'd try everything that's not quite as dramatic as this, but if no luck, this might be what's going on.

[stroudj]

Loose carb fuel bowl on the 914 is a common problem. Lose of power over 3500 rpm is a symptom of loose fuel bowl.

[grantopperman]

Carb issues might make sense given the recent circlip AD service....

[Cluemeister]

Would the hesitation stop when you went past 4000 rpm? Was the stumbling only happening in that range when you did your run up?

[grantopperman]

Hesitation prevented it from going past 4000. Every time it approached that, it stumbled and then power came back on at a lower rpm and started spooling up again. It only happened at that rpm, though. If I could fly all day at 3500rpm, I'd be golden.

I did not notice any anomalies in the initial runup prior to the takeoff run.

[buzz]

I would check the gascolator as Ed said. I had similar issues when bringing my plane home from Sebring. We found the screen in the gascolator to be about 75 percent blocked with debris. But as others have said if you just had the carb work done the bowls are worthy of being checked.

[buzz]

Dec 26, 2019 23:40:39 GMT Ed Midgley said:

I would open the gascolator to make sure it’s not a fuel flow problem. I tried to take off once with the fuel pump breaker pulled. It ran fine until take off power was applied. After about a hundred yards it fell back to idle.
Ed

Me too. Wasn't trying to take off but I did the same thing. I always pull the breaker if I'm on shore power working on my avionics. Took the plane out on the ramp and started it. Ran fine until it started to stumble at 4000 rpm. Needless to say I don't forget to check the breakers now on preflight. The other thing that came to mind when I did this was the issue of having two electric fuel pumps. I thought it was interesting that I was able to get 4000 rpm on a gravity feed. I guess I was thinking that if both pumps were dead that the engine would stop. I am not brave enough right now to test it in the air and pull the breaker but this oversight on my part left me with the impression that we might possibly be able to get up to 4000 rpm in the air if we loose main power and battery goes dead. Obviously would look for an airport if electrical system is lost but maybe we can still have partial engine power if pumps are dead. Thoughts? 

[montanapilot]

Buzz-

I would have the bowls checked as well as the bowels.

Sorry, I couldn't resist that.

[buzz]

Dec 27, 2019 14:57:12 GMT montanapilot said:

Buzz-

I would have the bowls checked as well as the bowels.

Sorry, I couldn't resist that.

Yikes!

[Cluemeister]

I'm guessing the carb bowls aren't fully sealed. I had a similar problem to this with my 914. The bowls were overtightened, and slightly warped. They worked ok until higher rpm caused them to lose their seal, and the engine would sputter. Acted fine at lower rpms. I think there are two bowl torque settings floating around (no pun intended). Lockwood said there is a new (lower) torque setting. I had them replace my bowls using the new torque spec, and the problem disappeared.

[grantopperman]

Thanks everyone for your ideas. I'll post back updates as I work to solve the problem. Meanwhile, I'm so thankful for our community!