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Low end bog - 95 Response


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Looking for help on an issue.  I’ve got a 1995 Response with around 600 hours on it.  This summer I’ve been experiencing an issue where the engine bogs down in the low end when trying to pull skiers out of the water.  Once it gets past the bog it runs like a top.  It’s not so severe that it won’t run but it makes it a little harder to tug me out since I’m a pretty big guy.  Then last night it wouldn’t start without revving the throttle which is highly unusual.  It always starts first crank.

The local repair shop is 3 weeks out on a diagnostic.  I’m thinking it has to be fuel related right?  The boat has the Mercruiser 350 with fuel injection.  I run 91 octane non-ethanol and have put multiple tanks through it this summer since it came out of winter storage.

Any help would be appreciated.  

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BlindSquirrel
1 hour ago, andrewml said:

Looking for help on an issue.  I’ve got a 1995 Response with around 600 hours on it.  This summer I’ve been experiencing an issue where the engine bogs down in the low end when trying to pull skiers out of the water.  Once it gets past the bog it runs like a top.  It’s not so severe that it won’t run but it makes it a little harder to tug me out since I’m a pretty big guy.  Then last night it wouldn’t start without revving the throttle which is highly unusual.  It always starts first crank.

The local repair shop is 3 weeks out on a diagnostic.  I’m thinking it has to be fuel related right?  The boat has the Mercruiser 350 with fuel injection.  I run 91 octane non-ethanol and have put multiple tanks through it this summer since it came out of winter storage.

Any help would be appreciated.  

Yeah, I would agree a possible fuel issue. Have you changed the fuel filter(s) yet? What about the fuel lines? She's getting up there in age, might need to start replacing the rubber parts soon if you haven't already. 

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I change the filter every spring.  I use the standard mercruiser filters.  Probably should upgrade to a more high quality filter I suppose.

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I would suspect a filter if the bog were at the top end rather than the low end.  You didn't say if it was a throttle body injected or multi port injected engine.  Either way, get the throttle body clean inside before you throw parts at it.  A can of spray carb cleaner will do it.  Open the throttle and get all the way around the horn and the edge of the butterfly, including any side passages.

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Posted (edited)

It’s the throttle body injection.  My air cleaner was a little dirty but the throttle body is clean as a whistle.  I’ll douse it with some cleaner regardless and then run it next week.  I don’t coexist well with the surf boats on the lake so I’m taking the weekend off and will run it next week.  It runs like a top in the shop on a hose but it only ever really bogs down at the lake when it’s under a load pulling out a skier so the hose test doesn’t really tell me much.  Thanks guys for the help.

Edited by andrewml
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  • 4 weeks later...
Posted (edited)

Just posting to give an update and hopefully get more help.  Thanks to those who have responded. 

I have changed fuel filter, visual inspected and tested the rubber fuel line from the tank to the filter, cleaned out the flame arrest or and throttle body until it is clean enough to use as a soup bowl, checked spark plugs for color and condition, checked spark plug wires.  I read in another thread about a small screen on the intake side of the fuel pump that gets clogged.  I have a mechanical fuel pump and I have removed the intake line and there is no screen.  Fuel system primes when the key is turned on.  I have put at least 100 gallons of gas through it this summer and have been adding Sta-bil 360 marine injector/fuel line cleaner in every tank.  I use exclusively 91 octane non-ethanol.

I have not pulled injectors, or tested fuel pressure regulator with a pressure gauge.  I don't really know how since my fuel lines are all solid and there is no where to splice in a gauge.  I have not done anything to the fuel pump other than disconnect the lines and visually check for any obstructions/problems.

The boat symptoms are:

-  Does not start well.  Turns over and over and over and usually will not start until I put the boat in neutral and give it lots of gas.  Every start prior to this year has been on first crank like clockwork.

-  When under load pulling a tube or a skier out of the water there is a noticeable hesitation/bog when shifting from neutral and applying throttle.  Once it gets past the hesitation the boat runs just as well as it always used to.  WOT runs about 40 MPH at 4400 RPM with me, my wife, and three small kids in the boat.  When the boat is in neutral there is no hesitation when throttling up.  Only does it in gear and only really noticeable when under a load.

-  The boat frequently idles at about 1000 RPM which is unusual.  Used to always idle around 600-800 RPM.  Sometimes will idle like normal, sometimes at higher RPM.

-  The last two times I have had the boat out it has been horribly inefficient on fuel.  Like 10 gallons per hour or worse just cruising around the lake or pulling my kids on skis.  This is a huge change as the boat usually just sips gas.  I have checked everything for a leak in the fuel system and there is nothing in the bilge or the water or the somewhere on the boat.  

I have owned the boat for 4 years and everything else about operation is the same.  I have performed all the required maintenance every year.  Oil pressure gauge is the same as always and temp runs about 130-150 which is the same as always.

I am thinking that I have to have some kind of problem with my fuel pressure either with the pump failing or the pressure regulator failing.  Any advice or ideas are appreciated very much.  It is virtually impossible to get any kind of service appointment in my area as everyone is at least 4 weeks out.  The Malibu dealer prioritizes boats that were purchased from them despite the fact that they have only been open in the area for a year...  I had an appointment with them and towed my boat the 1 hour plus drive on the day of my appointment only to find out that they were still at least two weeks out on service despite the fact that I made the appointment 3 weeks earlier.  

I've attached some pictures of my motor for reference.

 

5345EF5C-115A-40BF-9C4E-119FE191FC22.jpeg

634BF0B1-631F-43D5-AF99-AD2274487727.jpeg

Edited by andrewml
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High idle suggests an intake (vacuum) leak.  Needing throttle to start could also indicate a vacuum leak.

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2 hours ago, justgary said:

High idle suggests an intake (vacuum) leak.  Needing throttle to start could also indicate a vacuum leak.

@justgarythat’s also what I’ve been thinking just unsure of how to track it down

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1 hour ago, andrewml said:

@justgarythat’s also what I’ve been thinking just unsure of how to track it down

Maybe spray some starting fluid at the base of the throttle body and around the intake manifold.  You should get a distinct RPM bump when you hit a leaky spot.

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@andrewml - Have you noticed when you start the boat if it seems rich or lean, does it puff black smoke on start up?  Your excessive fuel consumption implies a rich mixture while running, have you checked to see if leaking injectors?  Opening up the throttle plates at start up may also simply be allowing the necessary air to enter system.  High idle does indicate maybe a vacuum leak or the throttle plates are not shutting properly, is the linkage free, throttle return spring doing it's thing?  Have you pulled spark plugs to see what mixture looks like?

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BlindSquirrel

Prolong? I loved their infomercial back in the day when they added prolong, removed the oil pan plug to drain the oil. Then drive it around town… never an issue! And here I am… still keeping oil in my engines like a sucker.

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  • 2 weeks later...

@justgary I tried the starting fluid trick and never got any indication of a vacuum leak.

@Woodski to my eye and knowledge the throttle linkage/plates/spring is working as it should. I did not pull all the plugs but I pulled a couple and they seemed to be in great shape.  At this point I’m ready to pull the injectors and have them tested and cleaned.

Last night I encountered a new problem.  Got to the lake and headed across to the glass for some ski runs and after about 1 min of running at about 30 MPH I noticed a hot/burning smell.  Temp gauge was at 120.  I stopped and opened the motor box and the smell was coming from the transmission.  Drive back to the dock and pulled the hoses off the transmission cooler.  Had a ton of junk on the intake side.  Transmission fluid was about 1/4 below the full hot line.  Cleaned the cooler out and ran it again with no problems it seems.  Gonna change the transmission fluid tonight.  Am I missing something?

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