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RPMs drop then raise when going into gear

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BigGib

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Hey everyone! I have a 2007 Four Winns 240H with a Merc 350 mag MPI and Bravo 3 that is having an issue when going from neutral into gear. It's dropping in RPM and then catching and raising to the same RPM as it was in neutral. In my previous boats it would just drop when in gear, so not sure what is going on here?

Tune up done last fall, just purchased this so no idea if it did it before the tune up or not. Thinking of trying IAC and filter first? It is missing the IAC filter currently.

Any help is appreciated!

 
i think you will find it is normal...most of the MPI engines have their ECU coded with a "stable idle speed" routine...so when you shift into gear, the IAC will open to maintain the desired engine RPM...

If you think there is an issue, have the ECU scanned...
 
Yeah it has nothing on the scan. Just odd it drops so low and then acts like it's catching itself before dying and raises. I've had quite a few 350 mpis, Volvo and Merc, and never had one do this? I'm hoping swapped the IAC will help
 
BigGib said:
Yeah it has nothing on the scan. Just odd it drops so low and then acts like it's catching itself before dying and raises. I've had quite a few 350 mpis, Volvo and Merc, and never had one do this? I'm hoping swapped the IAC will help
Click to expand...
IAC and or the filter for it would be my first look.
 
Well swapped the IAC and no change. What's odd is RPMs drop some in neutral and catch and raise back up when I turn on the captains call exhaust.

It has 3 batteries and cranks fine, and is charging at 14.5V
 

This first video is showing the RPM drop
in neutral when turning the exhaust on.


This second video is going in gear and back to neutral. Definitely have some pulley noise too.
 
BigGib said:

This first video is showing the RPM drop
in neutral when turning the exhaust on.


This second video is going in gear and back to neutral. Definitely have some pulley noise too.
Click to expand...
Not sure that would bother me that much, would be more concerned about the squeaking. What do the volts do when you see this happen do they drop? Assume the captains call draws some current? Is the noise a rough alternator?
 
Not sure about the volts when this happens, I'll run it again this week and see if it drops at the same time or not.

Not sure which pulley is making the squeak. Is there a way to easily test this without removing the belt?

I'm on a river, if I were on a lake it probably wouldn't bother me at all. Just hate to have an issue that gets worse and winds up leaving me stranded.
 
BigGib said:
Not sure about the volts when this happens, I'll run it again this week and see if it drops at the same time or not.

Not sure which pulley is making the squeak. Is there a way to easily test this without removing the belt?

I'm on a river, if I were on a lake it probably wouldn't bother me at all. Just hate to have an issue that gets worse and winds up leaving me stranded.
Click to expand...
Unless you can hear which one is noisy no remove the belt check and see what doesn’t spin freely. Can also be rust on the pulleys.
 
I'm going to check the belt/pulleys this weekend when the weather is better, same with the voltage when it's dropping.

Talked to the dealer I bought it from, they are saying it's normal and it's the computer cutting timing like a shift interrupt switch would on an alpha drive. Just doesn't seem right to me, my 5.0/Bravo 1 didn't do this, neither did my Volvo 5.7 GXI's or my 454mpi/Bravo 3's?
 
Why not connect a laptop if available with the correct software and see what happens when the rpm drops?

maybe it will show something of note?

Just a suggestion.
 
Unfortunately I don't have the software and from what I saw it's around $300. At that point I'll probably just pay a shop to look at it.

I cleaned the IAC passages the best I could and the throttle body with carb cleaner. Also swapped out the switch on the throttle bracket because I couldn't tell if it was opening and closing properly.

Also fixed the squeak. The belt was ran wrong and also too loose. Ran it the correct way and tightened it up and fixed the squeak.
Here is a video showing how it's running now and also the volt meter when it's doing it.

 
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