Surging on turbo engine

[DonMuncy]

 

When climbing out, the engine began surging. The prop RPM was constant, but the manifold pressure would drop from 40” down to about 35” for a few seconds and then go back up to 40”. It repeated that about every 10-15 seconds.

 

When leveled off and I set it up for cruise, it stopped doing it and all indications were normal.

 

Any ideas

[Bryan]

Sounds like a wastegate issue.  Do you have the Merlin?

[Vno]

In a previous turbocharged airplane I had a similar issue and it ended up being hoses going to the density controller had gotten hard and cracked. Vibrations would make an intermittent leak and cause surging. As part of your troubleshooting I would check all hoses in and out of your turbo system to see if they are intact. Do it by feel if you can since the way we found this one was the mech grabbed hold of a hose and it broke apart like PVC pipe. It looked normal otherwise.

Brian

[DonMuncy]

No, it is not Merlyn equipped.

Thanks Brian, we will check.

[81X]

It sounds like bootstrapping, and a pretty significant case.  To my knowledge, there's no density controller with a fixed wastegate non-Merlyn 231 so a density controller is probably not the issue.  However, hoses and intake components could be loose causing this. 

Two or three other things also come to mind to talk to your A&P/Hangar Elves about - First, your popoff valve could be opening at 40" instead of about 42" causing the pressure to go down and then close back at 35 or so causing it to go back up.  Wash, rinse repeat until you lower MP to cruise.  

Second, how long has it been (calendar) since your FI system was overhauled?  leaking o rings caused me to go from 36" to zero power on the runway; I had fuel in the upper deck somehow, it was in need of an overhaul.  If it's been 10 years or more, it might be time to consider an OH of that.  I don't think this would cause a big MP change, but if you can get your engine monitor data to see what fuel flows were doing, that may help provide supporting evidence 

The only other off-chance item that comes to mind is related to the Continental SB regarding the primer diverter leaking.  I'm not sure that would fluctuate the MP that much, but I guess it's possible under the right circumstances.  Other engine readings at the time can help confirm/rule this and the above item out.   

[stevedietrich]

My first guess would be an airleak somewhere between the turbo output and the individual cylinder runners.   If the  hose clamps are not tight the hoses will "walk" a bit.  Also puts a lot of stress on the runners to the cylinders.  A hint when the airplane is being serviced is to put a small mark  where the hose end should be on the manifold and runners so that it is apparent if the hoses are walking.