Merc 90 FS stalling when going from WOT to neutral/idle

[wrd1972]

Well figures. Got a problem with my 08 Merc four stroke.

When running WOT or even a bit less. If I quickly shift to neutral/idle when moving, the motor stalls out completely. Then when trying to restart, its very hard to do so. I have to move the shifter into forward a bit for it to start. Seems to be getting more repeatable.

Otherwise, the motor runs perfectly when at any give speed. Never once has acted up there...just when coming to a stop.

Thoughts?
Thanks

[justrfb]

Hello wrd1972...

I have an 07 Merc 75 4 Stroke that has been running absolutely flawless since the dealer we bought the boat from 3 years ago replaced the whole dual fuel pump assy... I had a boat full of people on the lake Monday and the same exact thing you described happening to your Merc happened to me. My wife is very leery of the engine not running right since we had so much trouble when we first bought it that she freaks out when it doesn't start right away. Pulled some tubers for a while, heading back in I was up around 5K RPM and I could feel the prop was loaded with weeds... Dropped it quick to idle, shut it down, raised the motor to clear prop, drop it back in and.... RRRrrrruuuhhh, RRRrruuuhhh, RRRrrruuuhhh... No start! WHAT!!! I get the look from Annemarie (my wife)... I waited a few moments, and then it started... She asked, "What was that?!!!"... I said, don't know and we were off.

So, I am very interested in knowing what others say too. I suspect something in the fuel delivery system... I am hoping mine is OK. You ever have an issue with the fuel pump/reservoir? It is the canister looking thing on the front of the motor with the fuel lines going to it... It has a low pressure and a high pressure fuel pump in it and it and it also has a float assy as it acts as a mini fuel tank... When it gets low, the low pressure pumps pulls fuel into it and the high pressure pump is the one that delivers the fuel to the injectors. It is a very expensive part and is trouble on our beloved Mercs... Anyway, I will be watching this thread. Good luck...

Sincerely,
Rich

[Soonertoon]

Check out my post from last summer "Mercury Blues" . Sort of the same issue. I traded mine the third time it happened.

[wrd1972]

Rich,
If you you determine that you have a WOT or partial throttle issue and it feels like the engine just starves for fuel and wants to sputter and die, the fuel float switch (Part #10 in the attachment) is the most likely cause. I had this happen years ago and it was replaced under warranty and it has run great since. However, if I need to replace one again, I will do it myself since it looks rather intuitive. Word has it these are a common issue on Merc four strokes.

My problem is definitely not a fuel starvation problem since it only happens transitioning to idle. I am leaning towards a gunked up IAC (Idle Air Control) valve. I plan on purchasing a new one and trying to clean the existing or just simply replace it. Does anyone have any knowledge of IAC valve issues causing stalling?