Noisy Starboard transmission...rich engine

[bud37]

It seems to me that it is virtually impossible to accurately diagnose these sorts of things when you are not there.....just some helpful tips hopefully and like dewmyster said, getting properly trained good help , there is just not enough useable info imho......dont sweat it yet 405driver, may just be a sensor forcing the ecu to overfuel the engine or under air it, and for sure it will run like you are describing. Just take your time and check off all the boxes which I am sure with your training you are doing....good luck man....

To add, I remember changing plugs one time and engine ran worse than before, found the offending cylinder and put another new plug in and all ok.....brand new plug was faulty.....just a story to illustrate my point that there can be any number of things to cause your issue , so important to get good help....

[405driver]

Good advice....always welcome....

Thanks

[405driver]

All,

OK...here is where we are today with the engine saga. What's coming out of the starboard exhaust is fuel (running rich). So, our local mechanic and I decided to check the fuel pressure. I have no idea how to do this, but he had all of the equipment to run the test and was very familiar as to how to do it. The fuel pressure test location is on the front top of the engine, just in front of the big metal cover (which I suppose is part of the intake) that says Horizon on it. Anyway, in looking at the vacuum hoses located there, one was found to be off. We reconnected it, hooked up the fuel pressure gauge and started the engine. The fuel pressure was about 30 psi, when we disconnected the same vacuum hose, the pressure jumped up to about 40 PSI. Reconnect it and it went back down to 30 PSI?? He says that at 30 psi, the engine will run rich???

We took the oil filler cap off and there doesn't seem to be any blow by coming out of the crankcase.

His thinking is that it might be a bad sensor somewhere. So, tomorrow morning we are going to hook his computer up to the engine and see if there are any error messages that might shed a little light on the issue.

Fortunately, it appears that engine itself is OK. At least he thinks so.

Any advice that I can quote? Might make me sound half way intelligent.

[bud37]

Told ya.......maybe some misguided soul pulled that hose to get more air in the engine to overcome the rich condition ( create a vac leak).....sounds like you are on the right track, you'll get it....do you know what the actual fuel pressure spec is ???...dont quote me on anything, just nod a lot.......

[405driver]

Thought that very same thing..
I think it's 43 psi from what I could find on line.
More tomorrow.....

[km1125]

I'm guessing that vacuum hose went to the pressure regulator. This way, the fuel pressure is always at the same pressure relative to the manifold vacuum. So when you have 15" of vacuum (which would be about normal for idle), then you'd have about 7.5 less PSI on the fuel pressure (air pressure is 14.7 PSI).

That would definitely make it run rich at anything less than full throttle. Full throttle, where you have very low manifold vacuum, then you'd be running about right.

And I think 38 PSI would be about right for a static engine (non-running), so it should be about 30 with the engine running at idle.

(and if it was only running 30 all the time then under load you'd be running LEAN)

[bud37]

km1125, I have a question for you as I have engines that have all this stuff..would love to understand this.....are you saying the fuel pressures stated in the spec are gage pressure or when you take a pressure reading do you add 14.7 atmospheric to it ???so with the above example the 30psi at idle would be 44.7 spec.....somebody has obviously been playing here..... :beer good:

Edit here,..... reread and I want to be clear I meant to say that someone has been fooling with 405's engine previously.

[405driver]

So, if I understand you correctly, when we checked the fuel pressure with the vacuum hose off, it read to high (40). Then when we reconnected the hose, the fuel pressure dropped down to about 30. Again, if I understand correctly, the fuel pressure returned to what it should be at idle....which is where the engine was...about 800 RPM????

That sort of sounds like the loose hose might have been the problem....??

If we connect the pressure gauge to the engine and then increase the RPM, would that prove anything concerning the operation of the fuel pressure regulator?

Thanks for the info......I'll figure this out yet.....

[km1125]

Source of the post km1125, I have a question for you as I have engines that have all this stuff..would love to understand this.....are you saying the fuel pressures stated in the spec are gage pressure or when you take a pressure reading do you add 14.7 atmospheric to it ???so with the above example the 30psi at idle would be 44.7 spec.....somebody has obviously been playing here.....

With a gauge pressure you're already reading something that has the 14.7 added to it, so when you read 30 PSI at idle, it is 30PSI. The regulator is set to 38PSI, so if there was NO VACUUM, then you would read 38 PSI. However, when there is vacuum applied (to that little hose) it lowers the gauge measurement to 30 (or 30.5ish) but if you actually measured the pressure from the input of the fuel injector to the output of the fuel injector, it would be 38PSI.

[km1125]

Source of the post So, if I understand you correctly, when we checked the fuel pressure with the vacuum hose off, it read to high (40). Then when we reconnected the hose, the fuel pressure dropped down to about 30. Again, if I understand correctly, the fuel pressure returned to what it should be at idle....which is where the engine was...about 800 RPM????

That sort of sounds like the loose hose might have been the problem....??

If we connect the pressure gauge to the engine and then increase the RPM, would that prove anything concerning the operation of the fuel pressure regulator?

Thanks for the info......I'll figure this out yet.....

Yes, it sure sounds like that hose might be the problem.

If you just increase RPMS under no load, then the intake manifold doesn't change much, so the fuel pressure won't change much. Put it in gear and open the throttles, and you'll see that pressure drop to 30ish pretty quick.