2006 75hp 4stroke EFI dies when throttling down

[Wiread]

I have a 2006 merc 75 4stroke EFI. Late last year when I was running at cruising for a while throttled back for a no wake zone it died. I did it more abruptly than normal so I kind of chalked it up to that. It fired right back up so I just moved on.

Now this year, cold, it fires right up, turn key and it's going. idles fine, runs fine. It's about 40 minutes to our sandbar as I only cruise about 15mph and it's a combination of that and some stretches of no wakes. If I don't throttle down in about 3-4 stages, it cuts out and it started getting harder to re-start. 5 seconds of cranking or so and quick put it into gear.

That happened yesterday in every no wake zone after it was warmed. once it was running though, smooth and easy like normal at idle or cruising. and fortunately for us, it did it again as we were approaching our slip was a very hard re-start and going from forward to reverse or vice versa killed it every time which we need to make the turn into our slip. I ended up getting it re-started after about 10 or so total seconds of cranking and had to pretty much put it in gear as I was cranking to keep it going and was able to get close enough to some piers and then turned it off and used a pole and loop to pull us back to our slip.

I figure this problem has been building since last year, but I did remove the gas tank this spring to put down a new floor on our pontoon not sure if that has anything to do with it. Gas is new this year as I drained the tank to remove it and burned that in our vehicles.

 

[Wiread]

small update incase it helps anyone help me

Every place is booked around here, almost a month ago I called around and July 20th was the soonest i could get in, including the marina I keep my boat at. Eventually found one that could get me in and got it over there.

They called me a week later and said it was good to go. They were to change the prop because I had marked it the last time out as I suspected it was spinning on the hub as well or I had a cavitation or air sucking problem. The marks moved so I knew it was spinning on the hub in addition to the engine issues.

all they changed was the impeller, which I wanted changed anyway, but said the rest was good. I thought it may be a temp issue which is why the increase with RPM's and losing propulsion seemed to happen more later in the day and not starting out. Figured the 2 might be related and higher temps were messing with electronics a bit and affecting it's starting performance when warm.

all this was mentioned to the marina when I dropped it off. Specifically asked if they ran it then tried starting it again as cold starts were not an issue and once it was started, running was not an issue either until cutting throttle back too quickly when warm.

Go pick it up after a couple weeks, impeller changed and old prop is still there. They tell me it's fine. I show them the marks and say, it's not fine. So they changed it quick. Then 4 days of rain and finally got it back in the water. Get a nice higher pitched whining sound at idle that goes away as soon as any throttle is applied, figure it's the new prop maybe?

but after 10 minutes all seems great, after 15 minutes, dies when throttling back. some trouble starting, 4 cranks and quick put in gear when it sounds like it wants to run, but can't, and it stays running. We run it half to full throttle back to marina and it runs smooth as can be and I really feather it back to throttle down and it doesn't quit until we get near our slip and I go from idle(F) to reverse, but we're close enough we can pull along the piers.

10 minutes of trying to start it again to no avail. So, i'm no further along than I was almost a month ago. it has to be something with temp and electronics, but i'm not sure where to start. I'm taking it to another place on the 20th, but just wondering if anybody has had similar I might mention to the mechanic?

I called the first one and told them what was going on and they told me they changed the impeller and it appears i'm having a new problem unrelated to the old one LOL. I'm like, I'm having the same exact problem I told you when I dropped it off. But hey, I can rent a trailer at 70 bucks a day to leave at their marina while they look at it again. It cost me as much in trailer rental as their "fix". Not quite as much, but it was a pretty good add on. I don't think i'll be taking it back there again.

 

[Wiread]

Small update, which leads me to another question. They went over the engine, no codes came up at all, but found the air idler valve was acting intermittently. So they started there. Waiting on the part so we'll see what that does. Definitely seems like it could be the culprit so i'm hopeful. Lost almost 2 months of boating already to this.

2nd question. I knew the motor had a lot of hours on it, it's an 06. They told me it had 950 and said I should probably expect a lot of things to need to be replaced soon. They said compression and everything was pretty good, but the parts around it start failing. any I should look for now and replace? just plan on getting what I can out of it and then repower or new boat?

Original plan was to upgrade the boat this year when we bought it 3 summers ago to see if we used it enough to get a nice shiny new one We do, but with the prices so inflated and boats hard to come by, we're waiting a year or so again. Unless I have to re-power then We'll probably keep this one for a while.

 

[Wiread]

In case anybody was following or gets a similar issue in the future, it did indeed seem to be the air idler valve that was acting poorly. Worked when cold, very intermittent when warm.

We've had the boat out a couple times now and it has been running great. No issues at all.

 

[marclind1234]

Curious if u had fixed yourself. Im having similar issue, replaced the IAC, but still doing the same thing, not sure if I need to somehow reset as I'm assuming it needs to be in the "out" position at start up limiting airflow.

 

[Wiread]

Curious if u had fixed yourself. Im having similar issue, replaced the IAC, but still doing the same thing, not sure if I need to somehow reset as I'm assuming it needs to be in the "out" position at start up limiting airflow.

I did not, I took it to a pretty reputable mechanic near our marina. I don't know a lot about outboards and I did read that something had to be reset with EFI when replacing that so I didn't even mess with it.