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2004 F115 IAC Valve Question
2004 F115 TXRC with the ever so popular sluggish 3500-4000 RPM symptoms. I have been honing my skills in becoming a Internet Outboard Mechanic and doing lots of research and buying parts and replacing stuff based on the statistics of what others have done to solve their issues. 
The short version of the question / issue? Running rough at 3.5-4K and inconsistent misfire. Cleaned/flushed fuel system, all new filters, new spark plugs, injectors sent out and prof. cleaned and tested. 42 PSI at shrader on fuel rail. Disconnected the IAC and problems go away. I think I answered my own question but don't want to assume too far on such an expensive part and also knowing the ECU should also be questioned. Thoughts?
Lots of different things that led me to this so sorry in advance if this seems long but could matter? Boat has not been in the water for a month except for testing and testing in a tank in the driveway.
History (if you have time to read it):
68 hours on this motor and I have only run it for the last 8. Fuel tank was emptied by the person I bought it from and claim that all filters were changed. First run of the boat went great. Cold water lake on a 60 degree day *****ing mostly but opened it up a couple of times. Trip 2 was to the saltwater. Again ocean temps were colder month ago but on this trip after a couple of short runs, it started to hesitate when trying to get up on plane.
Got home and the water separator was 1/2 full of water. I also noticed my oil had gas it it. Thermostat was frozen wide open. Changed that and the oil/filter and on my test it has held clean. Have not had it out since though.
I started it up on the muffs and noticed it ran ok but did not seem right. Got it into my test tank and idled it up a bit then noticed it was misfiring at the 4K mark and above. Took down to the local lake and ran it to confirm that it was bogging down at 3.5-4K and struggled to get up on plane.
After researching this, I suspected that the fuel system needed to be gone through. I replaced the water separating filter already with the yamaha one. The previous was a generic and shorter (although listed as 10 micron), fuel filter on the motor b4 the LPP, the one between the LPP and HPP, pulled the VST and changed that filter (was not dirty though had some particles from what looked like one of the screws in there corroding), sprayed out all the lines with seafoam and compressed air a couple of times, and send out all of the injectors to be cleaned and tested. All but one tested well before and after and all at 100% on return.
I did pressure test the rail and found it to be 42-44 PSI at 4000 RPM and 39 PSI at idle. I have tested separately on a second independant tank of fuel and put a clear line to the low pressure pump for testing and confirmed that no air is getting through to that point. No visible leaks anywhere on the fuel system running or not.
Still ran the same after all that work / parts. All things i don't regret doing though as I want that confidence in that they are clean and operating.
I saw some posts regarding the IAC valved being problematic only more so in regards to returning to idle. It does make a noise when turning the engine off and does idle ok at about 800rpms. I figured it was ez enough to clean so I pulled it out and sprayed some seafoam into it and let it sit overnight. Did not look dirty and could push on the end and feel it plunge. Put it back in today to do some more testing (fuel pressure again) and in the process forgot to plug it back in. ***, it ran great again. No misfire and although I did not take it above 4K in the test tank, at 4K it sounded good. I wondered if my test purged some air from the system and then noticed I forgot to plug the IAC back in. Once I did it returned to running poorly again.
I know the best course of action is likely going to be to bring this to a mechanic. I'm not looking for any silver bullet answers but do most of my own work as long as I have the tools and time to take on the task(s). Might not always be the quickest or cheapest option but gives me a sense of understanding of what I have and how it works. It took me years to find a good auto mechanic and he is very fair and honest with me. Have not found an outboard mechanic that I can say the same about and have been burned 3 times in the past from bad workmanship.
Some other info includes: high pressure pump does start up when key is engaged, water is passing through the system, engine warm but touchable, water is pumping through the cooling system, all fuses appear OK, full voltage from batteries, spark plugs each getting spark, all yamaha filters, oil, lubes, purged fuel tank completely (all gas was in good shape with no water), fresh gas put in with ring free and startron. Primer bulb pumps fuel and does not flatten out but I might replace it just the same as I have had these fail for me and it is an big dependency on such a cheap part to replace.
The short version of the question / issue? Running rough at 3.5-4K and inconsistent misfire. Cleaned/flushed fuel system, all new filters, new spark plugs, injectors sent out and prof. cleaned and tested. 42 PSI at shrader on fuel rail. Disconnected the IAC and problems go away. I think I answered my own question but don't want to assume too far on such an expensive part and also knowing the ECU should also be questioned. Thoughts?
Lots of different things that led me to this so sorry in advance if this seems long but could matter? Boat has not been in the water for a month except for testing and testing in a tank in the driveway.
History (if you have time to read it):
68 hours on this motor and I have only run it for the last 8. Fuel tank was emptied by the person I bought it from and claim that all filters were changed. First run of the boat went great. Cold water lake on a 60 degree day *****ing mostly but opened it up a couple of times. Trip 2 was to the saltwater. Again ocean temps were colder month ago but on this trip after a couple of short runs, it started to hesitate when trying to get up on plane.
Got home and the water separator was 1/2 full of water. I also noticed my oil had gas it it. Thermostat was frozen wide open. Changed that and the oil/filter and on my test it has held clean. Have not had it out since though.
I started it up on the muffs and noticed it ran ok but did not seem right. Got it into my test tank and idled it up a bit then noticed it was misfiring at the 4K mark and above. Took down to the local lake and ran it to confirm that it was bogging down at 3.5-4K and struggled to get up on plane.
After researching this, I suspected that the fuel system needed to be gone through. I replaced the water separating filter already with the yamaha one. The previous was a generic and shorter (although listed as 10 micron), fuel filter on the motor b4 the LPP, the one between the LPP and HPP, pulled the VST and changed that filter (was not dirty though had some particles from what looked like one of the screws in there corroding), sprayed out all the lines with seafoam and compressed air a couple of times, and send out all of the injectors to be cleaned and tested. All but one tested well before and after and all at 100% on return.
I did pressure test the rail and found it to be 42-44 PSI at 4000 RPM and 39 PSI at idle. I have tested separately on a second independant tank of fuel and put a clear line to the low pressure pump for testing and confirmed that no air is getting through to that point. No visible leaks anywhere on the fuel system running or not.
Still ran the same after all that work / parts. All things i don't regret doing though as I want that confidence in that they are clean and operating.
I saw some posts regarding the IAC valved being problematic only more so in regards to returning to idle. It does make a noise when turning the engine off and does idle ok at about 800rpms. I figured it was ez enough to clean so I pulled it out and sprayed some seafoam into it and let it sit overnight. Did not look dirty and could push on the end and feel it plunge. Put it back in today to do some more testing (fuel pressure again) and in the process forgot to plug it back in. ***, it ran great again. No misfire and although I did not take it above 4K in the test tank, at 4K it sounded good. I wondered if my test purged some air from the system and then noticed I forgot to plug the IAC back in. Once I did it returned to running poorly again.
I know the best course of action is likely going to be to bring this to a mechanic. I'm not looking for any silver bullet answers but do most of my own work as long as I have the tools and time to take on the task(s). Might not always be the quickest or cheapest option but gives me a sense of understanding of what I have and how it works. It took me years to find a good auto mechanic and he is very fair and honest with me. Have not found an outboard mechanic that I can say the same about and have been burned 3 times in the past from bad workmanship.
Some other info includes: high pressure pump does start up when key is engaged, water is passing through the system, engine warm but touchable, water is pumping through the cooling system, all fuses appear OK, full voltage from batteries, spark plugs each getting spark, all yamaha filters, oil, lubes, purged fuel tank completely (all gas was in good shape with no water), fresh gas put in with ring free and startron. Primer bulb pumps fuel and does not flatten out but I might replace it just the same as I have had these fail for me and it is an big dependency on such a cheap part to replace.
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