2007 225 pro xs rough idle

[backlash75]

Just had my 225 Pro XS tuned up a couple months ago. Replaced plugs, fuel filter, impeller and gear lube. Ran great for 3-4 trips but the last couple of trips it has a rough idle to the point it sounds like it's going to die. Once you give it gas it smoothes out and has no problem while under load. It only happens at idle. Ideas? Seems like I remember it doing something similar before and I changed gas stations where I fuel up and it cleared up. Been using the same station since with no issue until recently. Think that station could have changed their fuel supplier? It's a BP station. I also run marine stabil and quicklean every time I get gas.

[Savage]

Check the throttle plate air gap. Serial number is required when posting.


http://www.bbcboards.net/mercury-3-l...uncements.html

[backlash75]

1B507040.... forgot to put it in.

[EuropeanAM]

Definitely check the throttle plate airgap.

I would also recommend removing and inspecting the spark plugs to confirm they are:

-Correct Spark Plugs
-Correct GAP
-No cracks or fractures in porcelain
-Not FOULED.

Running Quickleen in EVERY tank of fuel? And Optimax/DFI oil?

[backlash75]

May have found part of the problem. I removed the red fuel filter, looked into the housing and had crystalized hose liner. cleaned all that out. I had my hoses replaced a couple of years ago, could this debris have been in there since then? If so, wouldn't that mean the tech didn't check this housing for debris? Or, could the debris have gravitated back to the tank and is just being sucked into the filter housing over time? Since I found debris in this filter housing, is there anywhere else I need to check?

[Savage]

If it where mine I would replace all the fuel lines again along with the primer bulb and filter. Replace everything all at the same time.

[backlash75]

Does the main black line from the tank to the bulb need changing also? I've heard that you don't have to change that one since its a different type of line. And Don, yes I use opti dfi oil and quicklean each time I fuel up. Plugs looked fine.

[Savage]

I would change ALL hoses. It is not worth the risk of power head damage over $30 or so worth of hose.

[EuropeanAM]

I would definitely recommend replacing ALL of the hose (all at ONE TIME) so you can rest assured it's no longer a problem.

[backlash75]

Ok. What powerhead damage can come from this?

[EuropeanAM]

Fuel restrictions can cause a lean-running condition (which in turn can cause piston/cylinder failure).

[backlash75]

Finally was able to get the boat to the shop and they had time to start on it. Plugs are fine. He said when he dropped #4 cylinder the sound/miss cleared up. He's thinking it's a reed valve based on symptoms. His bore scope broke so he's going to pull the front of tomorrow and check. Question, do I go back with carbon fiber or have one stainless reed valve? I hardly run wide open full rpm. I'm guessing about 5400 @68mph is all I've needed. He said if I didn't max out rpm I wouldn't notice the difference using stainless. That the carbon fiber reeds mainly are needed for 6000rpm. Does that sound about right? I'm planning on keeping the boat 8-10 more years. Does mixing reeds cause any long term issues? My hunch says go back with carbon fiber since when stainless breaks that piece poses through the engine instead of vaporizing. Thoughts?

[rchavis]

Correct go back with the carbon fiber reeds? If one is broken .

[EuropeanAM]

Use ONLY carbon fiber in this engine (that's what it came with, that's what should go back in it).

Available through Mercury... we also keep them in TDR.

[backlash75]

Well, the saga continues......Tech said the reeds were fine. But he replaced the o-rings on the air injectors and said that helped. He is going to take it to the river in the morning to test run it. Then he went on to say that there is now another problem. That when he went to turn the key on this morning(not sure if he just meant to ACC or actually cranking the engine) that there is a constant horn. He said that he has seen this before and it is the "horn circuit" in the computer and I will need a new computer now at about $1800-2000. Does this make sense? Can you help with some follow up questions I can ask to see how this mysterious circuit just fried when I've had no other problem with the horn. Could this be true and a slowly dying computer cause this rough idle in gear?

[EuropeanAM]

The direct injector o-rings are certainly a possibility (as are actual MALFUNCTIONING direct injectors).

As for the warning horn- there is indeed a PCM failure mode that causes a CONSTANT warning horn, with NO FAULTS. It is quite rare... but it does occur (and there's a specific test to verify the horn circuit in the PCM that can be done to confirm a failed diode).

I would, however, be very interested to see the following reports in PRINTED format:

-Run History
-Freeze Frame (Fault) History
-Fault Seconds Counters

(just to confirm there is no actual ACTIVE fault occurring).

[backlash75]

Update: I talked to the Tech, he took the boat to the river this morning and he said it ran like a top in all RPM ranges. No miss/skipping/sputtering, no going dead in-gear idling. So it appears the injector o-rings fixed that problem. Mercury is covering the PCM.

[EuropeanAM]

That sounds like good news, then.

[bassassin600]

i have an 08 pro xs doing the same thing. so was it the air injector o rings or the fuel injector o rings?

[backlash75]

The tech said it was the air injector orings. He said 2 had a slight tear, so after he saw those he replaced all of them. I'm supposed to pick it up this week sometime and I'll ask more questions about what all they found.