Noisy Starboard transmission...rich engine

[km1125]

Unless you see the fuel pressure bouncing around when it's idling, I wouldn't change the regulator. They are relatively inexpensive, but also fairly simple so not a whole lot can go wrong.

Are both engines running from the same fuel supply, or is here a tank dedicated to each engine? If you can switch them (on mine it's easy to switch either engine to either tank), then I'd do that and run it for a bit before I dove further into parts.

[405driver]

I can change tanks from the right main to the aft tank. Good idea! Do you think that bad fuel could cause a rich mixture?
Now that you mention that, maybe a good look at the fuel filter might be in order...



Thanks

[km1125]

Not necessarily a rich mixture, but it can cause a misfire, which would also affect idle stability. Of course when you get a misfire, you get that raw fuel out the exhaust because there is no where else for it to go.

I don't think just running a little rich would give you liquid fuel in the exhaust... more carbon certainly, but all the liquid should be gone. Just running a little rich wouldn't cause the idle speed to wander all over the place, but a misfire would. Running just a little too lean does cause misfire and unstable idle speed (not saying at all this is your case, but likening the unstable idle to what you're seeing, more than a slightly rich condition).

If that vacuum line was disco'd from the fuel pressure regulator, then that DEFINITELY was causing a slightly rich condition at idle. Might ONLY explain why your old plugs were much darker than they should have been. Knowing that you changed and corrected that, you might want to re-establish all the existing symptoms so you're starting fresh with a diagnosis. What exactly do you know to be true right now based on current observations?

[405driver]

OK.....here goes.

1. The transmission rattles in idle....still true
2. There is still fuel in the exhaust (at idle). A small slick comes to the surface and then immediately disappears.
3. The idle "hunts" slightly as confirmed by listening to the motor and watching the computer. The other engine fluctuates on the computer also, but this engine seems to vary more.
4. The engine starts,runs and accelerates very smoothly. It's just having issues at idle. I don't know if the fuel remains in the exhaust above idle. I will check that tomorrow. Strangely, the IAC computer readings on this engine were twice the readings on the other engine.

I'll know a little more tomorrow after the compression check. (which I'm a little worried about).

If I can figure out how to do it, I'll try to post some screen shots from the computer (maybe a video) and some pictures of the fuel pressure gauge with the vacuum line connected and disconnected.

I'm also going to switch fuel tanks.


Thanks...

[bud37]

Just had a thought, (I know unusual for the morning but)....before the big wrenches come out, try removing the IAC from the offending engine and inspect it to see if stuck or gunked up....if so clean and replace then try again with laptop attached to see if readings change....really do not want to start another path for you here, but that thing is real easy to check.....thats all I got , good luck man.....

[405driver]

Hey....I appreciate any idea.

There is an old axiom called "Ockumsrazor" that states "the simplist answer is usually the correct one". So, I keep looking for a "simple" answer.

I'll do that today......thank you.

[bud37]

Source of the post Hey....I appreciate any idea.

There is an old axiom called "Ockumsrazor" that states "the simplist answer is usually the correct one". So, I keep looking for a "simple" answer.

I'll do that today......thank you.

Trouble is, that don't work on multiple choice exams methinks........

[405driver]

Really never worked for me in college......

[Viper]

Hunting was one of the questions I asked in my first post if I recall. Exactly which ignition components have you changed? I still think it may be one or more cylinders aren't firing. Remember, you want to get the ignition system back to spec so you can eliminate it as the culprit, and it's regular maintenance anyway. So if all you replaced were the plugs, you haven't done enough and shouldn't be throwing any other parts at it until you're confident it's not ignition related. If we had a dime for every thread talking about the $$s spent in throwing parts at a problem and hoping for the best, we'd all be rich. If you're going to throw parts at her, replace the ones that are part of regular maintenance that will eliminate a system as the culprit so you can move on to the next system.

Was fuel pressure confirmed and compared to spec? I assume so, and that it didn't meat spec, otherwise why is he recommending regulator replacement? Was a fuel pressure gauge left on the rail and checked a while later to see if it maintained pressure? Was a cylinder drop test done?

Did anybody ever suggest hooking up a vacuum gauge?

Was there a determination made regarding the IAC reading?

While the diagnostic tool was hooked up, what was the voltage reading?

[Viper]

You either have bad fuel as mentioned above, a bad fuel system component such as leaking injector, a bad IAC, ignition problem, or the ECM is over-fueling due to a sensor input.

Besides the IAC reading, were there any other sensor readings that stood out? Was the engine hot when the diagnostic tool was hooked up? Does this (fuel in water) continue when the engine is hot at idle? What was the temp reading on the diagnostic tool? Does the oil smell like fuel? Is it at the correct level?