Neither turbo spooling up Man D28 v12 mechanical

[Nicholas]

Looking for troubleshooting suggestions. Here’s where we are: I recently completed cooling system service and replaced fuel cooler after it failed, leaking sea water into tank.  Got water out of tank, changed primary and on engine filters, all had some water in them. Boat ran fine after repairs – temps looked good, etc.

After about an hour of running, tried a WOT test. Both engines made rated RPM+ (~2350) throttled back. My mechanic thought the stbd engine lagged a bit spooning up, I told him I thought it was just the throttles not synced up well  repeated WOT, and heard a sound somewhere between a squeal and a whistle from stbd side of boat. My mechanic thought he saw gas venting from the outboard side of the stbd motor but wasn’t sure. <br />I throttled down. Tried to throttle up again and stbd engine wouldn’t go above 1500rpm, with more throttle just producing a lot of black smoke.

Checked all air hoses and clamps, no sign of a leak. Turbo spins freely by hand. Changed all fuel filters again. Airseps cleaned. Motors run fine ri 1500, but stbd won’t spool up. Any throttle beyond 1500 just produces tons of black smoke. I’m now stumped.

I’m somewhat new to twin turbo engines. Are there a certain subset of problems that would keep both turbos on the stbd motor from spooling up? I’m leaning toward an air problem despite the earlier fuel issue since the black smoke seems to indicate I’m getting lots of unburnt fuel. There is no appreciable smoke (or difference between the engines) at low rpm. No signs of hot spots or temp problems. 

Topic

[Nicholas]

I thought the same thing I just don’t see what it could be. The airseps are also only 2 years old and I don’t see any sign of deterioration or anything. Only thing I could think of would be…and this would be awful…maybe the techs when disassembling the engine for cooling system flush used the filter as a bucket to put nuts and bolts in…then maybe they forgot a washer or something in there when it went back on. I guess if so we’ll find it when we disassemble everything looking for the blade. 

[Rob Schepis]

Could something in the air filter assembly itself let go and get sucked through ?

Rob
"Luck is the residue of good design."

[Nicholas]

Mystery solved

Despite the fact that the turbo spun freely, upon closer look it threw a blade. Suspect the blade is downstream somewhere, maybe stuck in the charge air differential diaphragm or maybe in the intercooler. <br /><br />

In any case, the turbo is shot and didn’t realize it until a closer look with the airsep pipe removed.

crazy thing is the turbo is almost brand new – replaced in 2021, probably less than 100 hours ago, by the previous owner according to my documentation. Seems very odd for a blade on a new turbo to just break off. The tips of the other blades don’t look good either, although I attribute that to it being out of balance after throwing the blade. There is no perceptible wobble in the rotor that would suggest the blade was broke off due to a dynamic tip clearance issue. 

almost like something hit it, but that doesn’t make sense either because I’ve never run it with the airsep removed. 

[Nicholas]

No I have no boost pressure or EGT readings. I plan to add both. At this point, I know my boost pressure is zero or close to it because the turbos make a very audible whine, which I can hear on the port engine but not the starboard so it’s obvious the two on the starboard are not spinning up.

I agree with your instinct – I’ve had these exact symptoms a handful of times before on different engines and every singe time it was a busted hose clamp or split hose. But I’ve gone over them all and can’t find anything. Suppose one could be collapsing internally so will try replacing any that aren’t brand new (most are).  I was just trying to figure out if it was possibly something a little less obvious, like a waste gate stuck open or something like that, but I don’t understand how both turbos would be affected as it seems the only place they are connected to each other is on the exhaust side. Everything else seems independent. 

[Tony Athens]

Most likely a turbo boost leak . Every connection from the turbo to the aftercooler to the engine intake needs to be looked very closely. Most leaks  like you describe occur before the aftercooler because the air is much hotter.

Everything you posted points to that direction  Do your instruments measure boost pressure & EGT? If not, with engines of this caliber, IMO, you are driving blind.

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