Problem With Marquis Penta Engine

All 3 doesn't sound like a motor problem. It sounds like a fuel delivery problem.

I could agree on the fuel delivery problem but we have heard about electronic problems related to the Electronic Vessel Control system (EVC)
and the internal electronic engine control (EEC) systems of IPS systems, as all three engines are controlled through a single black box and throttle quadrant (or two with Flybridge boats). A bad connection or a cold solder joint on a circuit board may not be reproducible by the Volvo Rep at the dock.

I guess there is a problem with one of the engines and since they are synchronized in the higher revs, all are stalling....

That's exactly what i meant, I forgot about the synchro part.

It is like on the SR-71 Blackbird. If one engine stalls at Mach 3+, the other engine is engine turned off automatically, to prevent the aircraft from braking apart, due to asymmetrical thrust .

Btw. Seamanship is airmanship at 10 Kts .

With triple IPS you have two throttles and the center engine follows when both are in forward gear. From a certain rev all three are synchronized.

Normally you should have an error code if there is an engine problem. It can also be a problem with the EVC-boxes, sometimes caused by a thunderstorm. Another problem could be with a propeller, if it is damaged so one engine is halted, all will probably get the same signal...

My first thought was the sync. (We had a similar problem with our stbd. motor which had me going for the Racors until I realized it only happened when the sync was engaged.) Does the proplem occur if you bring them up manually without syncing?

Or a dirty bottom or running gear. After reading your update I'm changing my thoughts. Is #6 the last cylinder of every engine before you get to the exhaust riser? If so it sounds like the exhaust risers are not designed correctly and allowing water back into the last cylinder. Is the turbo in between the riser and exhaust manifold? If you have a dead cylinder the turbo's might not spool up and have a lot of corrosion also. How much boost were they making? Does it make full RPM in neutral? Has a lot of weight been added, especially to make the vessel sit lower in the stern? A dinghy, etc.

I'd expect a dirty bottom to be more evident through the entire range, also wouldn't expect a lot of growth in March, but it would fit. The #6 cylinder issue sounds like a design issue that would have affected the running from the start, not all three together suddenly 5 years later.

If it's the last cylinder before the turbo and exhaust riser on all 3 engines and the risers are too short allowing a little saltwater or freshwater to seep back into the engine, it's going to end up in the closest cylinder. For all 3 to have low compression on #6, it's REALLY odd. Also, the pistons, rings, and cylinder liners are the same parts in cylinders 1-5 as well as 6.

Hi We are looking at A 50' marquis. Has this been resolved? Do you mind sharing the resolution?

Hi Jim, did you buy the Marquis 50´??. I am planning to buy one and appreciate feed backs since nobody posted more about the problems!!.