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1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
Re: 1998 350 Mariner 5.0 Merc 3000RPM WOT
- CptBacardi
- Deck Hand
- Posts: 93
- Joined: June 11th, 2017, 5:02 pm
- Vessel Info: 1989 Carver 38 Santego (not an aft cabin)
- Location: Texas
- Has thanked: 3 times
Re: 1998 350 Mariner 5.0 Merc 3000RPM WOT
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
Re: 1998 350 Mariner 5.0 Merc 3000RPM WOT
@bud37 - my original post covered all of your questions, we have had the boat 4 yrs, it just started doing this summer, these are MPI engines (Merc 350s w Cool Fuel 2 pumps), batteries are perfect.
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
Here is my situation:
1. Boat will not go over 2800 RPM under WOT, in idle engines rev fine which seems to eliminate throttle or throttle cable.
2. Normal things all seem to check out ok; fuel filters, fuel vents & lines, fuel looks good, even pulled it and checked props, shafts and did compression check, also NO ECU codes are being thrown.
3. BOTH engines are behaving exactly the same
4. Under WOT, fuel pressure guage only reads 20-25psi and I believe it should be mid 40s according to Mercruiser. Voltage at the pump is also good.
5. Boat is a 98 with twin 350s with 600hrs (I believe the pumps are the Merc Cool Fuel Gen II, we have owned it 3 yrs and it just started doing it this season, worse is that 2 weeks ago it was limited to about 3000 RPM WOT, yesterday it seems to be closer to 2400 RPM (again BOTH engines)
I know this SEEMs like it must be the fuel pumps but it just seems so random that both fail the exact same way at the same time. I am just wondering if there is something else I should check or look at...looking for any and all suggestions PLEASE HELP. Thanks!
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- CYO Supporter
- Posts: 5803
- Joined: July 10th, 2015, 9:58 pm
- Vessel Info: 1989 Carver 3807 Aft Cabin
- Location: Ontario, Canada
- Has thanked: 431 times
- Been thanked: 1586 times
Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
If you have a sync gauge, disconnect it and go out for a test run. Then disconnect one tach at a time and test.
DO NOT do WOT in neutral
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
When I say I check WOT in neutral, I simply revved it for half a second just to make sure it would go above 3000 RPM to rule out throttle cable problem haha
-
- CYO Supporter
- Posts: 5803
- Joined: July 10th, 2015, 9:58 pm
- Vessel Info: 1989 Carver 3807 Aft Cabin
- Location: Ontario, Canada
- Has thanked: 431 times
- Been thanked: 1586 times
Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
Disconnect the sync and tachs at the gauges. Sometimes tachs can fail by shorting/leaking to ground and cause puzzling symptoms. The sync gauge hooks up to both tachs, and it's not impossible for a defective sync to pass on a problematic electrical issue to both engines. Depends on the unit you have but when I see something pop up that suddenly affects both engines at the same time and certain things have been ruled out that are common to both engines like fuel, source voltage, etc., considering how easy it is to eliminate the tachs and sync, it's a quick way to take that possibility out of the equation.
I recall seeing a bulletin about Cool Fuel II fuel pumps. Can you post one of your engine serial numbers.
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
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