Exhaust Pressure Fitting

[ajv00303]

See attached pic.
Replaced these last spring, only have ~100 hrs on them (Twin engines)
Both are clogged, 1 is burned.
They're not cheap, >$100 ea!

Last year was my 1st year w/ engines, thought I would check these, glad I did!
20230121_111548.jpg

[mactlman]

i cleaned mine in carb cleaner and a small piece of metal like a paperclip

[ajv00303]

How many hours were on it?

[mactlman]

How many hours were on it?

no software to know engine hrs--mine was tons cleaner and looked like new after a little cleaning. used amsoil oil and it stayed clean mostly

[ajv00303]

I use Carbon Guard 100% of the time.

[Bighare2]

Help us understand your duty cycle / usage cycle. Carbon build up is a sign of inefficient combustion.
Please tell us what is the most consistent cruising rpm that you run at.
What is the wot rpm at best trim and fastest top speed?

[ChampioNman]

Engine tuner does a good job also. Which one was burnt/ the one with 140? I can see the one at 90* clogged. They hate to idle.

[ajv00303]

Don't idle much at all.
I put ~ 100+hrs/season on my boat, typically May-Nov.
Usually cruise ~3800-4000RPM, ~30MPH.
WOT ~5200RPM @ ~40MPH. Maybe run there once an outing on the way back before getting to the slip.

Boat is a '95 Grady White 268 Islander, 27'. ~4600lbs w/o engines.

I am definitely enjoying these engines, just want to keep up w/ the maintenance.
Both of these fittings were clogged, 1 obviously burned (not sure 140* or 90*).

[Bighare2]

As a 175 hp your engine is propped at the bottom end of the wot range. Spec for a 175hp with Ficht direct injection is 5250 to 5750 rpm.
Full hp is always rated at the mid-point of the rpm range, so technically your engine is not reaching hp potential. Presuming the rpm as stated is accurate I recommend changing props to a lower pitch. Try to achieve 5600 rpm +- 100 rpm. Acceleration should be stronger and top speed may not change at all.
Your cruising rpms are typical but with the lower wot rpm the engine is seeing a heavier load and throwing more fuel in the cylinders at cruise. Combustion is incomplete thus creating more soot. This is called the “soot cycle”. Ficht direct injection is sensitive to this condition when wot rpms are on the lowest end of the range.

[mactlman]

what props are you running? changing 1 pitch will bump rpms 200-300?

[Bighare2]

This rig will need a minimum 2 in pitch drop. Most props are in 2 in increments and change rpm 300-400 rpm.

[ajv00303]

what props are you running? changing 1 pitch will bump rpms 200-300?

I am running 17"P props at the moment and like I mentioned I rarely run @ WOT.

Question: Does the EMM "pull" or "push" through the fitting? What is the purpose of the fitting?

[Bighare2]

The exhaust pressure fitting protrudes into the inner exhaust. The EMM is therefore sensing a pressure. The fitting does not restrict air movement. The service manual does call out a need for periodic service.
As mentioned earlier this technology is sensitive to carbon / soot buildup. The wot rpm needs to be increased. The issue is not that your do not run at wot but rather the load that the props put on the engine. At cruising speed the throttle position sensor senses a higher load and adds more fuel to achieve the torque necessary to run at the commanded RPM. The computer is doing what it is commanded to do but that does not mean what happens in the combustion chambers is as efficient as it should be. A pair of 16 pitch props may get the wot rpm what you need once the engine is allowed to develop its rated horsepower.

[ajv00303]

The exhaust pressure fitting protrudes into the inner exhaust. The EMM is therefore sensing a pressure. The fitting does not restrict air movement. The service manual does call out a need for periodic service.
As mentioned earlier this technology is sensitive to carbon / soot buildup. The wot rpm needs to be increased. The issue is not that your do not run at wot but rather the load that the props put on the engine. At cruising speed the throttle position sensor senses a higher load and adds more fuel to achieve the torque necessary to run at the commanded RPM. The computer is doing what it is commanded to do but that does not mean what happens in the combustion chambers is as efficient as it should be. A pair of 16 pitch props may get the wot rpm what you need once the engine is allowed to develop its rated horsepower.

Thanks for the explanation.