Turbocharged Manifold Pressure

[mshac]

My rear engine manifold pressure has been a little flaky lately. The gauge will fluctuate between say 29 and 31 inches in high-altitude cruise. I thought it was a sticky indicator gauge. It wouldn't do it all the time, but I did notice it.

The second to last flight, the rear engine would never make the same MP as the front at the same settings. It was about 2" lower. Again, I chalked it up to the gauge.

The last flight, once I got to cruise altitude of about 16K, I noticed the rear MP was at about 25" when the front was at 30". Again, it would fluctuate between about 23"-25".

My normal cruise speed was knocked down by about 15 knots, and the rear engine ran much cooler than the front at the same fuel flow settings.

The rear engine makes normal MP at lower altitudes.

So my question is this: Where do we begin troubleshooting?

The problem could be, IMHO, one of the following. Feel free to add to the list or expand on the correct testing procedures:

1. Cylinder(s) with low compression ( I'll do a leak-down test this week)
2. Intake manifold leak
3. Bad controller
4. Exhaust leak (prior to the turbo)
5. Bad turbo

Anyone with any experience chasing down this type of an issue, please chime in!!!

[wslade2]

I’m normally aspirated so little experience with 337 turbo. But have good deal experience with ground based turbo diesels.

Looks like good list.

Exhaust leaks are under appreciated and can be hard to find with surprising effect on turbo performance. The exhaust system lives in a tough environment so very much at risk. Exhaust leaking at the cylinder of course are their own doubly problematic issue. Also, if you have intercooler don’t forget to look at that. They can shake and crack with a resultant leak.

Air filters get overlooked because they look fine but at a micro level can get obstructed.

Frequently there’s a perfect storm of a little bit of everything: declining turbo, induction leaking, exhaust leaking, dirty filter. Don’t just jump in and sentence your turbo as guilty until you look at everything.

Of course carefully check for turbo shaft play and any rubbing on the housing or oil leaking out of the turbo into induction or exhaust. Any increased oil consumption?

[mshac]

Thanks for the reply.

I wouldn't have thought about the filter. I'll add that to the list.

The rear engine has oil leaks like many seem to. I think it's the pushrod tube seals that are leaking, but I'll look more closely around the turbo.

Experienced input is always appreciated!

[ljmolina]

I am having the same issue but on my front engine. I do know when I bought the plane 2 months ago, that one of the cylinders has a low compression (55psi). I havent been able to go down the list you posted...so that give me some additional areas to check for myself.

[mshac]

I'll post my findings here. To anyone reading, please do the same.

[mshac]

The plane does have a data-recording engine monitoring system. I may spend the $100 and send the files from the last few flights to Savvy Aviation for their experts to analyze.

Anybody here ever use their service before?