I am thinking of getting some plug wires so I can do the test for example with two set of plug wires and try on different cylinders if there is some difference. What do you think about this NGK TR 55 spark plugs could be this a problem? Regarding the ECM I am sure that this guy can not do the test but maybe I can get the ECM to test it I will call around tomorrow… but it is difficult to get the engines like that here. For the strange noice we still don’t know what is the cause I will try to upload the video… do you have some hints where to check for the vacuum leaks or how to check for it?

Thank you Brad for helping really appreciate it!!!

One more thing the guys said that that strange sound is idle air control could that be possible if there is engine is running perfectly fine on idle?

Vidic,

I’m certainly trying, as I know how frustrating it is to have a boat capable of so much more than it’s currently putting out.

Full disclosure…. I am about as far from an expert on engines as one could be. I’m a toolmaker by trade, so I’ve got a pretty good mechanical inclination, but I’m no engine guru. I have what I think makes sense, I have my empirical experience with MY engine, and i have the tidbits I’ve picked up through that process and what I’ve picked up by listening to the actual experts here on OSO. There are plenty on here that know FAR more than I do.

That said…..

My hunch, at this point, given all the other rabbit holes you’ve been down that have not panned out, is that you may have a physical issue with your ECM. A quick verification for this is to borrow one known to be good from the same engine, including the “HO”, and see if the behavior goes away. Outside of that, the only means of checking it is to ship it off somewhere for a scan. A pic from BoatsUnlimited website:




A video, with sound, would help the experts to figure out your “strange sound” while coming off throttle. Upload it to YouTube and post a link.

Thanks. Brad.

better make sure all power if off to the engine before messing with the computer, yes IAC will make noise when it cycles. I dont know about the plugs cant you get ones Mercury recommends.

Vidic,

To this, I'll say I've always stuck with ACDelco, but I don't think there's anything inherently wrong with NGKs, so long as they are the ones listed for your engine. A simple cross reference should verify that. I went with the high-dollar E3 plugs (~$8ea) in my last boat. They worked, but didn’t yield any gains. I’ve since sold the boat to a friend, and they are still going strong.

And, yes.... What Speedy said about all power being off. Before pulling the ECM, or even for just replacing the IAC valve, disconnect all power at the batteries.

Thanks. Brad.

I will try to call some guys tomorrow but I am not sure if I will be successful I think I will also try to get some wires for plugs from this second engine and then we will try to get to the cause… I will upload it for sure on the weekend.

i will change the sparks also on ACDelco and let me see the results. Regarding the power I am already aware that electricity is something you dont want to play with hahaha … I was a little bit afraid when I was doing the balance test but you know how it is … is something needs to be done you just do it!

For sure I turn off the power on the boat before I do something but anyway thanks! Regarding the sound I will upload the youtube video the sound comes for example when you put the throttle in neutral and when the rpms are dropibg this sound comes which is like you would squeeze the air inside it. The new spark plugs are going to go in for the weekend.

Vidic,

It's not so much that you're messing with electricity, but that you can potentially damage the ECM if it is still powered up while you start disconnecting the numerous connectors.

For the record, there's nothing scary between the ECM and the coils; not even the raw power supply to the coils. It's what's between the coils and the plugs you don't want to mess with. I doubt it would actually hurt you, but it will for damned sure make you find religion. It would likely be kind of entertaining for the other people in the boat, though.

Thanks. Brad.

Hello guys, it was few hectic weeks for me so I have not written the report… let us go back few weeks when I realised what happened. I bought Rinda testing usb device which you can plug to computer so you can see all the data from the engine. I plugged in Rinda and basically there where no errors. I tried to find the errors through the whole RPM range… and nothing!… but the engine was still under powered… So I decided to check the spark plugs … and you will not believe but in the first cylinder there was oil on spark plug… and the compression was also not the best on 5 cylinders cca 120 to 130 psi… and here we go again… engine is already out from the boat… new pistons, new bearings, …. Not good at least we have the answer.! Thank you all for your help!