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4.3mpi stutters above 3600

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mark123

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What are some things that trigger the guardian system. My 2006 4.3mpi will not go above 3600. It stutters if more throttle is given. Sounds like ignition cutting out, guess its limp mode . New fuel filter, oil pressure good, temperature good at 175. Gear oil good. New temp sensor. Could bad water pressure sensor at back of engine cause this? Left side of thermostat housing yemp sensor I did not change? I changed the temp one on right side. Everything works perfect up until exactly 3600. Prop is good and same one as before issue started. New plugs, IAC, fuel pump, both regulators, fuel pressure tested good, new cap and rotor. Oil level good. I did not change plug wires yet but intend to. Thanks
 
Honestly it often a waist to change spark plug wires unless an actual problem is found...OEM wires tend to last a long time in most cases.

Is the warning horn is sounding off at 3600? you'd probably be better off renting one of the 2 marine type of scan tools to see what the issue really is vs guessing.



Or place a bid on the hand-held scan tool though it comes with a different engine adaptor vs what you'd need

'''as the one offered is a special engine model...Buy the adaptor you'd need if desired.

If no warning horn, then check fuel pressure for other starting points.
 
Im in Canada so paying shipping and exchange etc...for a rental is too expensive, ill likely just buy one locally.
Fuel pressure is within spec at all rpm.
Another forum someone mentioned could be bad ignition sensor inside distributor, does that sound possible
 
mark123 said:
Im in Canada so paying shipping and exchange etc...for a rental is too expensive, ill likely just buy one locally.
Fuel pressure is within spec at all rpm.
Another forum someone mentioned could be bad ignition sensor inside distributor, does that sound possible
Click to expand...
While the Cam sensor inside the distributor seems less likely, honestly anything is possible at this point... The following may be of a helpful guide for you too should it be within these scenarios... Is the warning horn sounding off too at 3600 RPM??

www.crowleymarine.com

DIAGNOSTIC SUPPLEMENT FOR MERCRUISER ENGINES WITH EMISSION CONTROL TECHNOLOGY (ECT) | Service Bulletin | Crowley Marine

18-NOV-2011 - Manufacturer Service Bulletin: DIAGNOSTIC SUPPLEMENT FOR MERCRUISER ENGINES WITH EMISSION CONTROL TECHNOLOGY (ECT)
www.crowleymarine.com www.crowleymarine.com


Maybe a different idea to consider looking into too... Go to your local Canada craigslist, under services, look for marine and see if maybe there's a mobile marine boat tech that has a scan tool that could swing by and scan the engine for you.

^ Or get/buy either a smart craft gauge or mercruiser vessel view mobile app system to help scan for fault codes too...

 
Fun Times can correct me but is there not an "in gear" switch or connector that prevents over revving in neutral that limits revs somewhere in the 3000 - 3500 rpm range? This may have gone bad and the ECM thinks it's in neutral. It can be disconnected with no impact on anything else. I disconnected mine just as a pre-emptive measeure. I have a 2002 5.0 MPI.
 
My boat is an hour and a half from me or I would send a pic. IIRC it was starboard side top of engine VERY near the shift interrupt connection. Seems like it was blue/purple connector maybe. Worth a try.
 
Yes the engine in question would definitely connect up Garmin gps/sounder, etc. for more added technology on the boat and help read engine fault codes for general ideas of what is going on and possibly where to start looking but that system would take additional parts and connections points and add to as much as your budget desires all in which could be used for other boating benefits.

The list nowadays seems endless to add to and if that is something that you/one has a strong interest in doing/adding these options, I’d first suggest starting off studying online with a search of something such as mercruiser Garmin gps/sounder and see if the info leads you to wanting to go that route or not.

Plus a yes with Mark S. suggestion with the gear indicator switch could limit the RPM to right around 3600 if the ECM thinks it’s in neutral gear.
The following location of that item image is also in thanks to member AllDodge for making up each location mounted on the shift plate,
1785010106922.jpeg
 
Bingo.....wow thanks very much that was it. I unplugged the gear switch and everything working perfectly now. Im assuming no need to replace switch. Is its sole purpose to limit rpm in neutral?
 
That’s my understanding. It’s to stop idiots from over revving in neutral. Mine has been running perfect ever since unplugging it so apparently it doesn’t affect anything else.
 
With the gear indicator switch unplugged defaults to the ECM that you're in gear when it's not really...Should you consider putting a new one in if the old switch is ever found not to be out of an adjustment, then check out item number 20, merc part number 87-808009T11...




Glad you found the issue especially with Mark's assistance...hopefully now though with a lot of the info posted above ought to help get you guided for other ways to get you deeper into proper diagnostics vs guessing with tons of extra money at just parts...Finding and spending on the technology now may just help save later on buying parts wise... Weak point on these engines is the distributor cap plus a few other items like you just found.
 
Makes me feel good I helped lol. You can learn a lot on these forums. Most likely a shop would have went down rabbit holes trying to solve this amounting to $$$. Now Fun Times can help here...is there any risk to having it unplugged? Spinning a prop hub, loosing the coupler at speed for example before you can pull back on the throttle? I would think a momentary spin above 3600 wouldn't hurt anything.
 
This all started last year, 2 completely unrelated issues. It would stall at idle, running very rich. After taking out cool fuel module found regulator corroded and broke from fitting. Replaced that still not any better. Then found regulator on fuel rail was leaking, dumping fuel into manifold. Replaced that ( 618 at dealer 30 bucks from Friday parts lol) That solved the rich running/stalling but this 3600 rpm limit remained until now. Thanks again to y'all.
 
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