4.3 Mercruiser MPI Chugging/Surging and Beeping during turns/Waves

kylakoob

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Every time we turn/hit a wave the boat chugs/surges and loses power. It can get up to 50mph on a straight away, but the instant we take a turn or hit a wave and put it under load it sputters/surges and beeps. We have had it in over 5 marine shops, been told it was fixed multiple times but nobody can figure it out. Engine has less than 50 hours on it. Once you do a throttle reset (neutral) and take off again it does fine until cornering or hitting waves again.
 

dubs283

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Need to connect a diagnostic tool to determine what the fault/beep is. Being mpi the fault should be stored

What is the serial number of your engine?
 

Lou C

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I wonder if you can wiggle parts of the wiring harness to see if that can re create the surge. I’m thinking an intermittent connection is cutting power to the fuel pump or other component. That, or some debris in the fuel tank blocking the fuel pick up under certain conditions.
Agreed on getting it scanned as a first step.
 

Stinnett21

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Need more info. What did the 5 shops say and do? Surely someone scanned it. What were the codes?
 

Scott Danforth

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My guess a loose connection

Maybe at fuel pump

What is fuel pressure?at idle, under WOT, and when you hit a wave
 

Lou C

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All it takes with modern MPI engines is a bent/loose pin, or a bit of corrosion, & you can have those problems. Just disconnecting connections, inspecting, cleaning with contact cleaner and re-assembling (a bit of dielectric grease on the rubber seals helps keep out moisture) might solve it. Check relays for the fuel pump as well.
 

kylakoob

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They said it was not spitting a code. It just now started with the beeping, it did not do that before. We will take it out and try to wiggle things around. The 5 shops all replaced something regarding fuel. Lines, Pump, Filter, Gas, etc. One of them replaced an 02 sensor.
 

dubs283

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The 5 shops all replaced something regarding fuel. Lines, Pump, Filter, Gas, etc. One of them replaced an 02 sensor.

How about anti siphon valve or fuel tank pickup?

O2 sensor may indicate this is an EC motor?
 

alldodge

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Above my pay grade but might be something with the Adaptive Speed control @muc
Boat should keep the rpms constant but somehow the PCM goes into la la land when it's needed, but to even get started would need a serial number
 

muc

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Above my pay grade but might be something with the Adaptive Speed control @muc
Boat should keep the rpms constant but somehow the PCM goes into la la land when it's needed, but to even get started would need a serial number
I think you might be referring to a post I made on a Volvo Penta. Not all engines use this strategy. O.P. Didn’t post a serial number so at this point any advice would be a bad guess.
I see someone has recommended a “wiggle“ test. I would never recommend this test on a running MPI engine. There is a good possibility of hurting the ECM doing this on a running engine. This test should be done KOEO (key on engine off) with a scan tool connected.
 

Lou C

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That was me, this was commonly done by techs working on older Grand Cherokees & other MPI Chrysler products looking for faults that don't set a code (loose connectors, bad pins etc) but I didn't realize it could cause damage to a running engine. Thanks for pointing it out.
Now doing that with a scanner hooked up with the ignition on engine off totally makes sense. Don't want to hurt an ECM!
 

muc

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Read O2 sensor and might have CAT so don't know
Yes it seems that a lot of posters don't realize how important the serial number is to getting good advice. Even what would seem to be a minor difference --- say two engines that are the same, the only thing is one has freshwater cooling and the other has rawwater cooling ---- they will have different programs loaded to the ECM.

Without a serial number we just be guessing.
 

kylakoob

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I will get serial # as soon as I get home. I reached out because I have no clue- I did not know that was even a thing.
 
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