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I have a 2008 Mercury 90 EFI on my 170 Montauk. 4 times in the past two weeks when running at different speeds it feels as though the engine loses all power but still stays running. During the loss of power, even if I open it all full throttle it sounds as though it is not getting fuel and the rpms stay low. No warning alarms go off. The engine also runs very rough during the episode but quickly recovers.

By shutting the boat off and restarting it or bringing the throttle all the way down it seems to fix it and the boat runs perfectly. As I said it has only happened 4 times in the past 300 miles.

The gas is always fresh and the boat is run approximately 100-150 miles a week. Other than this intermittent issue, it runs great and feels and seems like a new engine.

It seems similar to how my old 2008 40 hp EFI felt when I lost a coil pack twice however the only difference is that this quickly resumes normal operation.

I spoke to the mechanic who does my work and he told me that it would be very difficult to diagnose until it goes completely. I am at a loss since I am basically being told that a breakdown is inevitable.

Any ideas or suggestions for me to look into is greatly appreciated, thanks

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I had a very similar issue on a carbed 60hp 2 stroke Mercury. I ended up replacing all the fuel line, the under cover fuel filter, and the transom mounted fuel filter/water seperator. This combo fixed it.

Maybe a fuel filter?

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How many hours run?
When were all filters replaced?
Fuel treated with stabilizer? Y or N
Last spark plug change?
Thermostat change?


I would start your process of elimination.

Running on a clean separate tank, new bulb and fuel line with fresh separator filter is a start.

Clean the vapor separator tank (VST) and replace the fuel filters (should be 2, low speed side and high speed side).

I think those two would eliminate fuel from the equation.

I would guess you have some crud somewhere that blocks flow. When you stop, it moves and the system is ok.

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[quote]Phil T wrote:
How many hours run?
When were all filters replaced?
Fuel treated with stabilizer? Y or N
Last spark plug change?
Thermostat change?


Thank you for your reply. I bought the boat the beginning of last season and the only thing I have done to it is change the oil and lower end fluid. The fuel has never been treated with a stabilizer and I am unsure how many hours it has on it. I can say with certainty that I would estimate that I have probably put on probably 250-300 the past two years. Prior to that I do not know what has been done. The strange thing is that I get no warning alarms in the Guardian system and it runs perfectly other than those few instances.

Wouldn't I get low fuel alarms if it was related to filters and an impeded flow? I do know that it has been at least 2 years or longer since spark plug change.

Three out of four times it happened it was within the first 5-10 minutes of operation. The other time it happened was after running for about 2 hours, shut it down for half hour then restarted it and it immediately bogged down.

Thank you for the advice, I will definitely have those all changed not knowing the past maintenance on it.

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I second (or third) the recommendation to start with the fuel system. Possibly get some quick silver fuel treatment \ cleaner to run through with a tank of gas.

Might as well do something while your waiting on a electrical problem to show up. Although I would put my money on fuel system

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Thank you everyone for the replies. I have changed the fuel filters and treated the fuel with mercury QuicKleen and the issue is still happening. It happened again yesterday within the first 5-10 minutes of running as it has been just as I began to throttle up and reach about 5000 rpms. I throttled down and after about 15-20 seconds it seemed to correct itself. I then took it out for 10 hours and did 80 miles in total and it ran great and never did it again.

What I have noticed is it seems to do it after not using the boat for 2 days and once it happens within the first 5-10 minutes, it doesn't do it again for several days.

Is it possible that it is something with the computer and sensors that need to be reset by shutting boat down? I am completely baffled and even the local Merc service rep stated that he isn't sure what it could be.

Thanks

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Does it smoke when this happens?

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No it doesn't smoke but the usually very quiet engine becomes louder, shakes a bit and definitely sounds rough but as soon as I shut it down or throttle back, it is back to normal for the rest of the day.

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Have you tried it on a remote tank yet. That will eliminate tank, fuel lines, external filters in one easy step if it still does the same thing on the remote. If it runs fine then you know it is one of the above.

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I will try the new tank tomorrow. The strange thing is is that if it was related to fuel that I would think (and I readily admit, I know very little about outboard repair) that it would happen all the time and not just within the first 5 minutes. Does anyone know if there are sensors or an internal battery in the engine's computer that may be malfunctioning and by shutting the engine down it resets something in the computer?

After it it happens for the first time, even if I shut the boat down for several hours while we are out or anchored off a beach, it doesn't happen again for a few days.

Thanks again for everyone's input

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I am slowly and hopefully narrowing this issue down. I tried the new fuel and new fuel tank today and had the exact same loss of power between the first 6-8 minutes of running the engine when going from about 2500 rpms to 5000 rpms. So up until now I have changed the 2 fuel filters, tried a fuel additive/cleaner and changed the fuel and the tank.

The only thing that I did differently today was when I lost all power I was at WOT and instead of shutting it down or throttling down, i left it WOT. Within about 5-6 seconds the engine seemed to recover on its own and then ran perfectly for the rest of the day again.

I have not checked the VST as I have no idea how to open or drain it on the engine. Does anyone think that it may just be accumulated water in this VST that is causing the issue? For some reason I thought this was under high pressure and had to be serviced by qualified tech (which is not me by any means)

This is driving me nuts, thanks for any further help.

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Doesn't your motor have a diagnostics terminal to allow a technician to scan the ECM for trouble codes? That's where I would start before changing filters, fuel, spark plugs, etc.

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It probably does. When I spoke with the mechanic who I know he said it initially sounded like an electrical issue but after listening to several different members here, many fee that that it may be related to the fuel system. I am only into it for about 30 dollars so far since it needed filters anyways and I had a spare tank.

The engine has the Guardian alarm system but I have never had an alarm during these episodes. Do you think an error code would still be generated even though the incident only lasts less than 10 seconds and no alarm is generated?

Thanks

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It happened again today at the same time (approximately 5-7 minutes into trip). I was running at about 5500 rpms and all of a sudden it dropped to under a 1000 rpms for about 5 seconds and then corrected itself and ran fine for rest of day. I changed the plugs which were due anyways and mechanic said he would not expect to see any error codes if no alarms were triggered so I haven't brought it in yet. At this point all plugs were changed, ran new fuel from separate tank and changed fuel filters. I do not believe it is fuel line because it is solid and issue only happens once per day. There is a high pressure fuel pump/vapor separator tank than I have no idea what to do with since it seems to be one piece.

Any other ideas?

Thanks

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What is strange to me is that your mechanic hasn't seen this problem before. Have you contacted Mercury Marine about it for some advice?

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Yes, I have attempted to contact them several times by phone and email and this is their response:

Dear Mr. @#$#@
Thank you for the email on your 90 horsepower engine, serial number, 1B521939. We are happy to address your questions.

Unfortunately, due to inherent safety concerns, it is very difficult to diagnose over a phone or email format. If you are experiencing issues with your engine, we would recommend working with your local authorized Mercury Marine dealers. If they have inspected and are having any issues trying to diagnose, then we would encourage your authorized Mercury dealer to contact our factory trained dealer technical service team for assistance. If you need assistance locating an authorized Mercury dealer, we would invite you to visit our website at, www.MercuryMarine.com .

Not much help as you can see

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Just a guess but is it maybe the choke malfunctioning?

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Can you get it to your authorized Mercury dealer, or is it too far to drive?







You could have a lot of things happening in a motor and boat that is getting run that hard. They have a diagnostic procedure that they are apparently not going to share with you for free. You might be money ahead to get yourself a Mercury service and shop manual for your motor.

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My father had the very same issues you are having on his 17 Montauk. not sure what caused it either? he heard some story that ethanol was breaking down fiberglass tanks and that was causing the problem. I don't really believe that story. anyway 2 shops later we got a plastic tank and just ran a new hose over the deck to the motor directly. we bypassed all the filters ect. for whatever reason that worked! we then went over the fuel system and replaced everything. things seemed fine after that. I think somehow the fuel system was sucking air somehow. he has since sold the boat so not sure how it is holding up. I am not a mechanic but we were desperate as no one could figure it out. we checked the stater and many other electrical parts to no avail. hope this helps let me know if you figure it out.

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Thanks for the info. I have tried everything now and even the certified Mercury tech who I know and trust is at a loss at this time. It did it again today, lost all power for 5-10 seconds then corrected itself and ran great for another 50 miles. I was hoping to get it squared away before I am done for the season up here but cooler weather is moving in and I am not sure that I will.

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So it does the same thing as if you suddenly pulled back the throttle (puts engine at idle) and the suddenly advance it back to where you had it.

Have you looked into the electrical parts of the throttle linkage - throttle position sensor, or whereever the throttle input goes into the EFI system.

Even if that's not it, I still like electrical - too sudden for fuel system, I think. Loose wire somewhere, maybe even a bad ECU (intermittent connection on a printed circuit board)

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Have similar problem. I'm installing a primer bulb. I believe that the fuel lift pump is bad. I will let you know how it works out. Don't know why there wasn't a primmer bulb.It was explained to me if there isn't any fuel like from running out of gas or bad hose connection that the lift pump an wear out by lack of cooling and lubrication.

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Hi Oldnstoked,

Does yours do this all the time or just within the first few minutes of operation? Thanks for the info, let me know.

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Hey Waco72
Mine just started a couple of days ago. Ran fine at cruising speed. Went o fishing spot. Anchored for 1/2 hour. Started to leave and it acted up at idle. Heard a blower sound coming from fuel module. After trying to start it and changing tanks it cleared up. Coming in I have a 10 minute 5mph zone it started again.
Thought it might be my bad tach sending a signal so I disconnected it and notice the foam on the air filter was 1/3 missing so I cleared the rest of the foam off. Started the engine and it ran fine at idle for a while. went for a cruise and it started acting up again. Called my mechanic. Put a diagnostic computer on it and nothing came up. Installed a primer bulb and went for a cruise and didn't act up. My luck when the mechanic is there it wont act up. He's thinking that the lift pump might be or is going bad. Installing the primer bulb so if it is bad I wont get stuck

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Update
Installed primmer bulb and new connector. Ran it without an issue until I stopped to talk to a friend for about 20 minutes. When I restarted an issue developed. Was idling rough and was stating to stall. Pumped the primmer bulb and issue disappeared. My mechanic is going to change the lift pump and I will keep you posted.

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Thanks,

My engine also sucked in a 2 pieces of my air filter last year, the alarm went off and it bogged down for a second. I replaced air filter and was fine after that. There have been other threads about it happening to others as well.

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Why do you think it happens? Also why didn't it happen again?

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I was told that it happens when the filter breaks down. It seemed mine became very tacky to the touch and pulled apart easily when it happened. I researched it and found out it was not that uncommon. I will just keep an eye on it now and replace it every few years. This one was 4 years old when it happened it it was two perfectly circular holes in the filter material on each side about the size of the intake. Do a search on this site and you will find others that have had the same issue

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Every few years? The one on my engine fell apart with only 90 hours on it.

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Update
Changed lift pimp and still had problem. Test and found a faulty float. Changed it and will test it. Took it out for 1/2 hour run and seems to be ok.
Oldy

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Great thank you, after all of the replies and things I have tried the problem seems to be getting narrowed down to just a few things. What kind of test did they do and was it an expensive job? In mine it almost seems like some type of float is getting stuck and then once it releases it is fine for few days. I appreciate the input

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The parts were about 400.00. If your doing the float you should do the lift pump. The bad float might have burnt out the lift pump. I did air filter and installed a primer bulb and a new connection to tank too. I need to put some hours on it but I think I addressed the problem.