2006 Monterey Boat with a 4.3L Mercruiser TKS Engine S/N 0w354897 Mysterious Loss of Power

[Fun Times]

On doing some refresh memory work of rereading a pass thread of someone losing power after time, you may have to perform an engine compression test along with doing an engine vacuum test to ensure the internal engine is healthy… Also take note of how to check fuel pressure on a carbureted engine like yours.

Pressure testing the fuel pump on a 2007 Mercruiser 3.0 TKS Mercarb

I want to run a pressure test on my fuel pump to see if that is what's breaking down after running for a bit on plane, ( http://forums.iboats.com/forum/engin...s-at-3000-rpms ) From what I can see it would require me to remove the rigid steel fuel line and add couple of barbed fittings and...

forums.iboats.com

Additional thoughts to add… Is the flame arrestor clean? When this event happens, have you opened the engine hatch and re-ran the engine up to RPM to see if it performs better again with fresh new air under the engine hatch?
Looking for suffocation.

How long have you had this boat to first notice this issue?

What service component were changed prior to this developed condition?

 

[Rosedeal]

Thanks for your responses. I replaced the water/fuel filter last September and I just didn't think any water could get into it since the cap outer rubber seal has always been tight in place. But I will remove the filter and dump the contents into a glass bowl to see if there is any significant amount of water in it.
But since you mentioned it what are your thoughts about how it could come into play based on the symptoms I described? My observation would be, why would the boat start up and run strong for at least 20 - 30 minutes before losing power? The carb seems to get fuel OK while in neutral and throttles up, but when I put the boat in gear, during the time the boat experiences the power loss, the engine wants to stall if I give it more throttle than just barely in gear. And after sitting a while in our boat lift, it will run strong for about the same period of time then lose power again.
My cousin, who is an avid boater, suggested I replace the rubber hose from the fuel tank to the water/fuel filter since he has experienced the inside collapsing due to the age of the hose. All good ideas, just nothing seems to pass all the logic tests as to why the boat runs at all and why the problem seems to persist each time after 20 or 30 minutes of running under load.

 

[nola mike]

Revving with no load tells you nothing. If there's water in the tank it's initially layered at the bottom and not necessarily picked up. As the boat bounces it gets emulsified in the gas and then sucked up. You stop and it separates out again. How does it get in? You're surrounded by water with an open fuel system. If it didn't happen you wouldn't have a water separating filter. This is common stuff that should be checked before looking for something more exotic. Also didn't catch if the carb is still tks. Either way have you checked that choke is open or tks plunger is not closing inappropriately?

 

[alldodge]

To rule out fuel, need to put a gauge teed online. If it's not fuel then something is getting hot

 

[Rosedeal]

nola mike reply: doesn't the fuel pickup in the gas tank extend down to the bottom of the tank where water would be since it's heavier than gasoline? That said, and the boat floating in the lift when I start the engine, could the engine be started with fuel left in the water/fuel filter and it run for a while before getting fuel pulled from the gas tank? Which, as you said, as the boat bounces it gets emulsified in the gas and then sucked up. So, at the start the boat is running along strong using the fuel pulled up from the tank and through the water/fuel filter, and it goes for about 20 - 30 minutes before suddenly decelerating and almost stalling before I back the throttle down to just in gear. The engine never fully cuts off. At this point the boat will only run about 3 -5 mph and if I try to advance the throttle more the engine wants to stall.
I know you said revving the boat not under a load tells you nothing, but isn't the same fuel, with or without water intrusion, being pumped to the carb regardless of under load or no load?
Please keep in mind, I've recently replaced the carburetor, plugs, plug wires, distributor cap, rotor and ignition coil and with that the engine sounds great, doesn't skip or sputter, and runs strong under load up until the moment it loses power.
The carb that was just installed is a TKS with the electronic choke which is also new. Usually when I start the engine and am waiting for it to warm up I listen for the flow change that occurs when the plunger changes positions.

 

[Rosedeal]

alldodge reply: thanks for your feedback. What is a gauge feed, where would it be placed online and what indication would it show? And if it's not fuel then what other components, getting hot, could logically cause the loss of power?

 

[alldodge]

alldodge reply: thanks for your feedback. What is a gauge feed, where would it be placed online and what indication would it show? And if it's not fuel then what other components, getting hot, could logically cause the loss of power?

Would need to remove the carb fuel line and place a tee fitting there. Can make one froma plastic or brass tee and some rubber fuel line and clamps.

Pressure should be 4 to 6 psi from idle thru WOT

 

[alldodge]

Was going to delete the past 3 post, going to do a folks, both of yall need to simmer down. Be respectful or don't post

Edit I'm deleting those post

 

[Scott06]

To rule out fuel, need to put a gauge teed online. If it's not fuel then something is getting hot

Agreed

to the OP if you can rig up fuel pressure gauge, take a timing light and spark gap tester. Go out stay close to the launch and when it happens make sure to see if fuel pressure is ok, check timing under load with timing light see if it is bouncing around. Check spark strength with gap tester both when it is running well to get a baseline for how far it will jump, then when it acts up see if spark is weaker. Basically need to determine if it’s intermittently fuel or spark.

intermittent issues especially if spark related can be very hard to nail down. Had a VW fox years ago haunted me for about 2 years, just need to think of it as checking off boxes and ruling things out

 

[Rosedeal]

alldodge reply: Sorry you had to delete those posts. I didn't realize there are posters that get offended when one shares observations of what is occurring or not occurring during the sea trial. BTW, I don't think I saw a response alldodge to my question about what component could get hot and lead to or contribute to the loss of power issue. Might provide a clue.
Well, I see I have some things to try based on posted suggestions so I'll see if they surface anything.

 

[Rosedeal]

Well I'm back with the mystery issue. Finally, after hurricanes and NE winds, was able to make my second sea trial. This time stayed relatively close to my dock. We did another test before the sea trial wherein we ran the boat until the problem occurred, about 25 minutes. This time with the flame arrestor off we sprayed some starter fluid directly into the carb and the engine picked back up. So we thought that pretty much pointed to a faulty fuel pump. Our thinking was that the boat was using the fuel in the fuel line, fuel pump and water/fuel separator before it ran out and the old fuel pump just keep up with the demand. That said I installed a new fuel/water separator filter and fuel pump. First sea trial after that, the boat ran smooth and strong and I thought after 25 to 30 minutes of running at various speeds, that the problem was fixed. So I finally had a calm river today to perform my second sea trial. Did loops again not too far from the dock and this time the boat performed smooth and strong for about 25 minutes and then I felt a bump in the power followed by a gradual loss of power. Also different this time is backing the throttle down to just in gear didn't work to keep the engine running. It finally cut off and would not start. I tried opening the fuel filler cap, didn't help. I took the flame arrestor off ad sprayed starter fluid into the carb, didn't help. I noticed what looked like fuel vapors coming out of the carb. Not sure if that was a clue.
So using my paddle I got back to the boat lift. This took about 30+ minutes to traverse the 300 ft I was away from the dock. Got the boat back in the lift, waited a little longer and tried to crank it back up. It finally did crank up and again, appeared to run smooth and strong.
So at this point all the major fuel and electrical components have been replaced and it hasn't solved the issue. Any additional ideas of things to try or experiences would be greatly appreciated.

 

[Scott06]

Well I'm back with the mystery issue. Finally, after hurricanes and NE winds, was able to make my second sea trial. This time stayed relatively close to my dock. We did another test before the sea trial wherein we ran the boat until the problem occurred, about 25 minutes. This time with the flame arrestor off we sprayed some starter fluid directly into the carb and the engine picked back up. So we thought that pretty much pointed to a faulty fuel pump. Our thinking was that the boat was using the fuel in the fuel line, fuel pump and water/fuel separator before it ran out and the old fuel pump just keep up with the demand. That said I installed a new fuel/water separator filter and fuel pump. First sea trial after that, the boat ran smooth and strong and I thought after 25 to 30 minutes of running at various speeds, that the problem was fixed. So I finally had a calm river today to perform my second sea trial. Did loops again not too far from the dock and this time the boat performed smooth and strong for about 25 minutes and then I felt a bump in the power followed by a gradual loss of power. Also different this time is backing the throttle down to just in gear didn't work to keep the engine running. It finally cut off and would not start. I tried opening the fuel filler cap, didn't help. I took the flame arrestor off ad sprayed starter fluid into the carb, didn't help. I noticed what looked like fuel vapors coming out of the carb. Not sure if that was a clue.
So using my paddle I got back to the boat lift. This took about 30+ minutes to traverse the 300 ft I was away from the dock. Got the boat back in the lift, waited a little longer and tried to crank it back up. It finally did crank up and again, appeared to run smooth and strong.
So at this point all the major fuel and electrical components have been replaced and it hasn't solved the issue. Any additional ideas of things to try or experiences would be greatly appreciated.

Did you have spark when it died? suspect not given the staring fluid did fire off. Would check for spark and verify 12 v at positive terminal on coil when it happens

 

[alldodge]

The fumes out the carb is just liquid fuel in the intake

Something must be getting hot and there is a bad connection stopping the fuel or spark.

Starting fluid worked before but not next time.

Use to idle but then wont'

Agree, need to check power

 

[Rosedeal]

Well I was so confident, after the first seemingly successful sea trial, that we had discovered the fix (replacing the fuel pump) that I didn't have any test equipment in the boat. So, no I wasn't able to check the coil output. I did however go back to my boat repair/maintenance log and discovered that I had replaced the ignition coil somewhere around April of 2020. We really haven't run the boat much since then so I had assumed that wouldn't be the problem. Until I read in the item description that "Over time the factory ignition coil packs can fail, leading to hard starting, losing power when the engine is hot, or your boat may run erratically". The boat is harder to start than I expected after replacing all the major components. And it did lose power about 25 - 30 mins after the engine gets hot.
That said, does that sound feasible that when the engine initially runs it would run and sound OK but when it gets hot the ignition coil could start to fail? And would also result in not being able to restart until the engine and coil cool down a bit? The coil is one of the easier components to replace so no problem there.

 

[Scott06]

Well I was so confident, after the first seemingly successful sea trial, that we had discovered the fix (replacing the fuel pump) that I didn't have any test equipment in the boat. So, no I wasn't able to check the coil output. I did however go back to my boat repair/maintenance log and discovered that I had replaced the ignition coil somewhere around April of 2020. We really haven't run the boat much since then so I had assumed that wouldn't be the problem. Until I read in the item description that "Over time the factory ignition coil packs can fail, leading to hard starting, losing power when the engine is hot, or your boat may run erratically". The boat is harder to start than I expected after replacing all the major components. And it did lose power about 25 - 30 mins after the engine gets hot.
That said, does that sound feasible that when the engine initially runs it would run and sound OK but when it gets hot the ignition coil could start to fail? And would also result in not being able to restart until the engine and coil cool down a bit? The coil is one of the easier components to replace so no problem there.

yes it is possible but would test it out either my ohm testing the coil see if it is outside the range and use a spark gap tester. Only seen coils fail when the sensor in distributor leaks current so the coil is building up energy when there is no spark to be made...

Also possible you have a loose connection in ignition circuit or man overboard switch is being tripped. I leave a small pack of tools including a volt meter in the boat, just to ensure I wont need them... in a pinch you can take plug out and hook it to coil wire to see if coil is firing.

 

[alldodge]

Don't think it's the coil, I'm still thinking a connection, maybe even the key switch

 

[Fun Times]

Do you recall the reason the coil was changed in 2020? Was it for the same reason you're experiencing now?
Do you still have the old one to try it again?

 

[Rosedeal]

Holy moly, why is this like trying to find a needle in a haystack? Is this a boat thing?
Saw this posting while I was composing this response.
To be honest I think I replaced the coil because the engine was running rough. The boat has only been experiencing this current issue over the last year or so. And no I do not have the old one.
The issue almost always occurs in about 25 - 35 minutes under load. Until then the engine putts and seems to be running strong. Not sure if that is the typical amount of time it takes the engine to fully warm up. But even today when the engine sits (cools off) a while it starts back up and sounds great.
Would the above description eliminate any of these suggestions?
For example, would a loose connection in the ignition circuit or a tripped man overboard switch always occur 25 - 35 minutes into the ride or would the key switch do the same? And after sitting for a bit work perfectly until the next ride under a load results in the issue occurring again? Not even sure how I would test some of those things.
The common denominator question seems to be; what changes when the boat runs for 25 to 35 minutes under a load that could result in a gradual loss of power to a point where the engine makes kind of a clinking sound just before it will just barely run in gear or cut off altogether? And then if it does cut off it will not start again until after about 30+ minutes.
I appreciate your suggestions

 

[alldodge]

The worst thing someone can do is replace parts before determining what the problem is first through testing. Replacing anything has a possibility of also induce another problem

Things like the coil can draw enough power if malfunctioning "might" lower the voltage enough to cause spark issues or cause a relay to de-energize. If TKS Temp switch starts to short out it might kill the power but when that happens it normally blows a fuse

 

[rolmops]

I like the clogged fuel tank vent. A friend of mine had a similar problem on his Penn Yan. It turned that in his efforts to make the boat nice and shiny , he actually clogged the air vents on his tank with wax. It made it hard to fuel up, because the air had nowhere to go and as in this case the lack of air supply in his tank caused a vacuum strong enough to severely limit fuel supply to the engine The little bit of air that slipped in would keep the engine running at a low rpm. I probably would never have a problem like that ,because waxing a boat is not my forte.