Noisy Starboard transmission...rich engine

[bud37]

km1125........Thank you sir for the response.....

[405driver]

A few more questions.....

Is there an inverse relationship between vacuum and fuel pressure so that with the vacuum hose disconnected, the fuel pressure would be higher?

Would it be correct to say that with a massive vacuum leak (hose disconnected), there is nothing controlling the fuel pressure regulator so that the fuel pressure might be at some random reading?

Would a reading of 40 PSI fuel pressure be more rich than a reading of 30 PSI at idle?

It's hard reason something out when know nothing about it...

Thanks

[bud37]

I have something here might help a bit....dont know if this applies to your exact engine setup but the basics will be here to help understanding.......enjoy the read....

http://www.pleasurecraft.com/manuals/L510004.pdf

[km1125]

Source of the post A few more questions.....

Is there an inverse relationship between vacuum and fuel pressure so that with the vacuum hose disconnected, the fuel pressure would be higher?

Would it be correct to say that with a massive vacuum leak (hose disconnected), there is nothing controlling the fuel pressure regulator so that the fuel pressure might be at some random reading?

Yes, you are thinking correctly.

The only thing about the "inverse relationship" is because of the way vacuum is measured. Normal air pressure is "0" vacuum and a complete loss of normal air pressure is 30 inches of vacuum. If you convert those to actual air presssure, than "0" vacuum is 14.7 PSI air pressure and "30 inches" of vacuum is ZERO air pressure (like in outer space).

You gauge pressure is anything ABOVE normal air pressure.

"Would a reading of 40 PSI fuel pressure be more rich than a reading of 30 PSI at idle?"
YES. What you're really interested in is the difference in pressure from the input to the output of the injectors which spray the fuel. Since the injector is really INSIDE your manifold, the output of the injector is in manifold vacuum, so it's EASIER for it to spray into a vacuum than if it was spraying into normal air pressure. If the fuel pressure regulator is connected to that vacuum, then it can compensate for any vacuum that may be present. Yours does, that's why you should be measuring fuel pressure at idle (high vacuum) at a lower pressure than when at full throttle (low vacuum). Make sense?

[405driver]

Makes sense.......thanks so much....

[405driver]

Mornin'

Here's the latest on my starboard engine. Yesterday we connected my mechanics computer to both engines to compare them. It appears all of the sensors are working. The RPM and timing were fluctuating a good deal more on the starboard engine than on the port engine. Also the IAC readings were about twice as high on the starboard as compared to the port (23/40). Not sure what all that meant and neither was he. Right now the plan is to remove all of the injectors and have them inspected/cleaned/rebuilt, maybe one or several are leaking. We also considered replacing the fuel pressure regulator as my mechanic says he has had symptoms like this before caused by a faulty FPR.

There are no fumes or back pressure coming out of the oil filler.

Considering everything else that I have found on this boat that has not been cared for, I would bet that the injectors have never been serviced.

The engine has about 750 hours on it.

Here's one more thing. I read somewhere that if the injectors are leaking, that if you turn the key off and on and off several time without starting the engine, that if an injector is leaking that the engine might be hard to start due to flooding, tried that, the engine started right up, no problem. probably BS.....

So really, I don't know anything definitive. I hate to just start changing parts on a "guess". The engine runs great, the throttles are even at all RPM's, acceleration is even with no spitting or sputtering, its just running rich (trans is rattling at idle), and showing fuel residue coming out of the exhaust plus blackened plugs that smell like fuel. The idle "hunts" as per the computer read out, and that's causing the transmission to rattle (I think).

We have not checked the compression but with the way this engine runs with everything pretty much equal, hard to believe it has a bad cylinder. Maybe low compression across the board could cause the computer to dump more fuel in....? That doesn't make sense to me, seems there would be more symptoms.

As per a post above, maybe I'll get a second opinion for the Mercuiser tech guys at a nearby marina. Our guy is very good and I hate to offend him as I may need "local" work in the future. He also works for our marina and I don't want get on the wrong side of them....but I want this motor to run right.

Is cleaning the injectors a good place to start, plus it can be done by our local guy?

Typing all of this kind of helps me prioritize what's going on since I really don't have a clue. Thanks for everybody's help and opinions....I enjoy trying to take something that isn't working right, figure it out, and then fix it.

[bud37]

Near as I can tell, you seem to be getting close, trouble will be figuring out who is yanking the chain first as that will be the cause....having a lot of experience with carb engines , fuel inconsistencies can show up as rich, lean,rpm hunting then creating timing advance changes.....one of the guys that really understands these engine systems will chime in soon, I wanted to thank you for posting the results continuing as others will learn from this ( I know I will) , so many just disappear and we never learn what advice worked.....

One thing I will add to this is the first thing we did before trying to tune an engine was to make sure it was mechanically sound, that would include compression testing to eliminate trying to tune an engine with lets say a bad valve or ........

[405driver]

I think you are right. A compression check has been in the back of my mind through this whole process. As the say...."shouldn't try to put lipstick on a pig".... I think I'll do that before anything else is done.

Thanks......I'll post the results.....

[km1125]

I'd certainly do that before buying any parts.

Do you still see the fuel in the exhaust after you reconnected that vacuum line?

Did you change or clean the plugs since you reconnected that line? You plugs might be causing a variation at idle. If you haven't already, you could probably just run them "at speed" for a bit to clean them up and then go back to working on the idle issue if it's still a problem.

[405driver]

Hi,

The compression check is scheduled for tomorrow afternoon.

Yes, the fuel was still evident in the exhaust after the vacuum hose was reconnected.

No, have not taken the plugs out since we fooled around with the vacuum line. I need take the boat out and run it a little bit and then look at the plugs. I think we'll do the compression check first and see what that says about the health of the engine then go from there. If that's OK then clean the injectors and maybe replace the fuel pressure regulator.

I will post the compression readings. In addition I intend to check the fuel pressure again both static and idle. I'll post that to. Finally, I'm going to hook the computer up again to both engines and try to video the readings while the engines are running. Hopefully several heads are better than two.....

Thanks