Noisy Starboard transmission...rich engine

[Viper]

I see the DIACOM readout but I'm having a hard time coming to terms with a couple of things. The IAC numbers are consistent with what I would expect to see in some apps on a warm engine depending on other variables but engine specs would confirm. I'm also not convinced that this app has an 02 sensor. The question then would be why is it displaying numbers for that input? Is it just a DIACOM default? Again, an engine serial number would really help here.

I like km1125's throttle plate setting idea....a definite possibility. We're not taking about the TPS so don't go thinking you should change it now

PS; unless I'm missing something, if this engine has an O2 sensor but is not a catalyst engine, then why the two O2 sensors? I say that because of the "Closed Loop" statement in the DIACOM readout. With no catalyst, I don't see the need for two O2 sensors and only one sensor is not a closed loop system but an open loop one. We need to confirm the app so we're not jumping to conclusions just because we see it on the screen.

[405driver]

The serial # is 0L003570. 454 Mercruiser MPI Horizon.

I'll see if I can get any info on the DIACOM app tomorrow,that's a really good point. I guess it could be the wrong software....

Thanks

[Viper]

So I did some checking on that Ser#; you do not have O2 sensors as suspected so I don't where that data is coming from unless it is a default mode but I'm having a hard time with that because I just fired up DIACOM, picked a suitable engine and could not get O2 data lines. That makes more sense to me. So while I understand why the O2 sensor voltage would be 0 volts, where is it getting data to indicate that the Fuel Mixture Status is "Lean" or that the system is in Closed Loop mode?

I also struggle with the "Fuel Flow Rate" It's actually giving a reading of 1.3 GPH. Where is it getting that data from? There is no sensor on this engine/vintage based on your S/N that would give the ECM any indication of fuel flow rate or pressure. It is simply relying on the regulator doing its job to maintain proper pressure so that the correct amount of fuel is delivered for a given pulse width.

So based on the above, I have to wonder whether the correct engine was selected when the diagnostics were done? Otherwise I don't know how you'd get some of the readings unless the engine has been modified. Other than that, the other readings seem normal to me.

The normal IAC count for a warm engine idle should be between 0 and 40 depending on other inputs.

Your fuel pressure should be 37 PSI with the vacuum line attached, and 43 with it disconnected. That's how you're supposed to check it to determine regulator output vs pump output. There are 2 regulators on your engine; one on the fuel rail and one on the cool fuel. ***So here's something to consider that I've seen before which is a definite possibility for over-fueling at idle; one of your regulators may have a torn diaphragm, fuel is leaking into the vacuum line and being sucked into your intake. This is a known problem that will also cause a rich condition at idle. This is also part of the reason why I asked if the fuel pressure gauge was left hooked up for a while to check if rail remained constant. It would point to the possibility of a leaking injector.

As mentioned earlier, you should ensure the IAC and by-pass passage are free of soot, deposits, carbon, etc.

[km1125]

I was writing this as Viper was posting the above comments, so I'm rewriting mine:

That is good data and much more specific to this engine. In my earlier post with 38psi, I must have seen pressure specs from a different Merc. But I'm confused by when you did the test taking off and putting on the vacuum line and said "The fuel pressure was about 30 psi, when we disconnected the same vacuum hose, the pressure jumped up to about 40 PSI"
You might want to re-run those tests to make sure you have good data.


On the IAC readings... perviously you wrote "Also the IAC readings were about twice as high on the starboard as compared to the port (23/40)."... so if the IAC most reacent reading was 38, then it is consistent and in the range Viper specifies for idle... that's better news.

[km1125]

Source of the post
Your fuel pressure should be 37 PSI with the vacuum line attached, and 43 with it disconnected. That's how you're supposed to check it to determine regulator output vs pump output. There are 2 regulators on your engine; one on the fuel rail and one on the cool fuel. ***So here's something to consider that I've seen before which is a definite possibility for over-fueling at idle; one of your regulators may have a torn diaphragm, fuel is leaking into the vacuum line and being sucked into your intake. This is a known problem that will also cause a rich condition at idle. This is also part of the reason why I asked if the fuel pressure gauge was left hooked up for a while to check if rail remained constant. It would point to the possibility of a leaking injector.

Do both of these run at the same pressure? I see both locations in the parts diagram and that they are both referenced to manifold vacuum, but does one feed the other, or do they both end up feeding the fuel rail?

[405driver]

Ok.... maybe an "ah ha" moment here. As I reported much earlier, when we started this whole thing, we found a vacuum hose off. I remember Scott ( our mechanic) saying that he thought he could see "oil" residue in the tube. I bet it's fuel and that exactly what you are saying could be the issue. He suggested that we change the FPR, so we are. So, the injectors are out for service and the FPR is ordered. I'll find the one on the rail and order that one also. Guess we won't know anything until we get it back together...
I think I need to make a contribution to the site for all this great help... you have no idea how much this is appreciated.

[km1125]

To verify, take the old pressure regulators and use a hand vacuum pump to apply a vacuum on the vacuum port. Pump it up to 15-20 inches and see if it holds. If it doesn't hold, that was a problem. You can seal the other two ports and then it should definitely hold, or your measurement is suspect.

Don't just guess at parts if there is a way to verify it. If you actually find the problem the symptoms are much less likely to reoccur!!

[405driver]

Words to live by....

[Viper]

Source of the post....Do both of these run at the same pressure? I see both locations in the parts diagram and that they are both referenced to manifold vacuum, but does one feed the other, or do they both end up feeding the fuel rail?

There were a couple of different versions and I'd have to check but if I recall correctly, the one by the pump in the CF module is doing the regulating and the one on the rail only acts as a dampener to smooth out pulsations.

If your version has the two regulators (probably does if the drawings are correct based on S/N), the vacuum line to both units should be checked for fuel. If all you're replacing is the regulator/dampener on the rail, you may be replacing the wrong one.

Again,....

Source of the post.... Don't just guess at parts if there is a way to verify it....

[405driver]

I think there is one in the fuel cooler... that's the one we are replacing.