Losing RPM on STB 350MPI Rinker 342

onislandtimeonislandtime Member Posts: 309 ✭✭✭
in Engine Discussions
At cruise speed STB engine RPM fluctuates. When at idle or low speed its fine. After stopped for couple hours and restart, gets on plane runs for 10 minutes and same symptoms occur. 
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  • WillhoundWillhound Member Posts: 4,217 ✭✭✭✭✭
    Is the engine actually revving up and down or is it a tach issue?
    If actually the engine is maybe suspect a fuel issue. Filter maybe.
    "Knot Quite Shore" - 2000 FV270 (Sold)
    2018 Cherokee 39RL Land Yacht (Sorry...)
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  • Liberty44140Liberty44140 Member Posts: 4,404 ✭✭✭✭✭
    Yep agree I’d so filters first, if you have cool fuel then you have two fuel filters per engine. Make sure to do both. 
    07' Cruisers 390 (Previous Rinker's: 06' 342EC & 01' 310FV)

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  • onislandtimeonislandtime Member Posts: 309 ✭✭✭
    Yes I believe its a fuel issue. The tanks are on 1/4 and the issue is becoming worse as the fuel gets lower. Going to change water/fuel separators and fill the tanks with premium gas and add stabilizer. Cheapest way to trouble shot right now.
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  • WillhoundWillhound Member Posts: 4,217 ✭✭✭✭✭
    Change the separators and the filters if you have them both. With age the filter material inside the filter cartridge gets soft and as fuel is sucked through they "collapse" which causes a restriction. In my opinion fuel filters should be a once a year thing. Under $20 and not hard to change.
    "Knot Quite Shore" - 2000 FV270 (Sold)
    2018 Cherokee 39RL Land Yacht (Sorry...)
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  • onislandtimeonislandtime Member Posts: 309 ✭✭✭
    @Willhound where are the filters located?
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  • GMSLITHOGMSLITHO Member Posts: 1,598 ✭✭✭✭
    You can add some dry gas it helps if it’s water in the tank 
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  • WillhoundWillhound Member Posts: 4,217 ✭✭✭✭✭
    edited May 2018
    Go here and either enter your engine serial number or look up your model. Someone with more experience can correct me, but I think some just use the fuel/water filter and some might also have a seperate inline fuel filter.
    http://www.mercruiserparts.com/

    Edit: Don't know if this is your motor or not, but in this page you can clearly see the additional fuel filter:
    http://www.mercruiserparts.com/bam/subassembly/31754/15322/60
    "Knot Quite Shore" - 2000 FV270 (Sold)
    2018 Cherokee 39RL Land Yacht (Sorry...)
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  • onislandtimeonislandtime Member Posts: 309 ✭✭✭
    I believe their is one on the bulkhead in the engine compartment. I just did'nt know if there were more.  
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  • pistolepistole Member Posts: 158 ✭✭
    edited May 2018
    There are the fuel water separators come filters usually mounted on the "firewall" in front of engines. On the engines themselves would be fuel filters that look exactly like oil filters  near the fuel pump
    Post edited by raybo3 on
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  • Liberty44140Liberty44140 Member Posts: 4,404 ✭✭✭✭✭
    Make sure to look up your engine serial number as Will commented. By 05 they stopped mounting the fuel filters to the firewall and stopped the inline and went to a coolfuel module which is mounted to the engine. It acts as a fuel filter and fuel water separator and it has two filters in it per engine. Not sure if this was the case in your 2004. I use marineengine.com to look at my engines diagrams 
    07' Cruisers 390 (Previous Rinker's: 06' 342EC & 01' 310FV)

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  • onislandtimeonislandtime Member Posts: 309 ✭✭✭
    Thanks @Liberty44140 I will check that out
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  • SpyderwebSpyderweb Member Posts: 915 ✭✭✭
    Liberty, 
    are there 2 filters inside each module?
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  • reneechris14reneechris14 Member Posts: 3,134 ✭✭✭✭✭
    21 and 26 are the filters  those are OEM numbers you can look up.
    2005 Rinker FV342  Pawcatuck river,Ct
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  • Liberty44140Liberty44140 Member Posts: 4,404 ✭✭✭✭✭
    edited May 2018
    Yep! As reneechris shows in the diagram parts # 26 and 21 are two separate filters. #21 is often overlooked and can absolutely cause your problem. It is at the very bottom under the large filter and may be so black you don’t notice it. Need to do both at the same time.
    07' Cruisers 390 (Previous Rinker's: 06' 342EC & 01' 310FV)

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  • onislandtimeonislandtime Member Posts: 309 ✭✭✭
    UPDATE: Changed water/fuel separator filled up with Premium and loaded up with fuel stabilizer. Ran it for and an hour and no problems. Thanks for all the suggestions and help!!!
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  • WildboatingWildboating Member Posts: 957 ✭✭✭
    Do you want to hear a story about losing rpm on the starboard motor??😂😂😂
    2003 Rinker 342 Fiesta Vee, 350 Mag MPI, Bravo 3 2.20:1 w/ 22p 4 x4 props

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