Merc 150 Intermittently Bogging Down at WOT

[oba97]

I have a 2017 Mercury 150L EFI that will bog down intermittently at WOT. I can idle and cruise at 3/4 throttle no problem, but when I go full throttle it will get up to speed then bog down a bit then go back up to speed. This will continue until I back off a bit. I changed the fuel filter but this still happens.

A little more info…..

When this first happened I had a boat with 4 kids on it so I didn’t want to dig into it too much at that time. A couple days later I went to go out and the boat wouldn't start. I trimmed down the motor but after that nothing worked. I pulled the battery and brought it home to charge (I keep my boat in a marina). As it turns out the battery was fine. So…I went back and cleaned the wire terminals as best I could because the had a decent amount of corrosion and then tried to start it. It started right up. But I have been out three times since and it continues to happen at WOT. I also don’t think I’m getting top speed anymore.

My gut says this is fuel related but could corrosion on the terminals cause this issue? I have read a thread about adjusting the shift cable so I might give that a shot.

Any help is greatly appreciated.

 

[alldodge]

Start by taking the fuel filter and dumping contents into a clear container to see if there is anything but clean gas. Then check fuel pressure to see if it falls off as you get to WOT. It might be a restriction in the fuel supply side or weak fuel pump

 

[QBhoy]

Hi. Is there a chance that you are hitting the rpm limiter ? What rpm are you getting at fuel throttle ?
Let me know if you can. If it’s not that…I might have an idea what alternatively it may be. But check it’s not just the rpm limiter first off, before I go into that. I’ve a similar 2016 engine to yours.

 

[BrianVT]

Start by taking the fuel filter and dumping contents into a clear container to see if there is anything but clean gas.

I'll 2nd that.
I had a similar issue and found clear plastic shards in my filter. It was the fuel lines between the tank and the quick connector at the engine. They are known to have a clear inner liner that degrades and falls apart.
I replaced them and the primer bulb. But the problem continued. It turns out that crap had built up in the quick connector and was restricting fuel flow at the ball valve.
Easy and cheap think to check and replace.

 

[QBhoy]

I'll 2nd that.
I had a similar issue and found clear plastic shards in my filter. It was the fuel lines between the tank and the quick connector at the engine. They are known to have a clear inner liner that degrades and falls apart.
I replaced them and the primer bulb. But the problem continued. It turns out that crap had built up in the quick connector and was restricting fuel flow at the ball valve.
Easy and cheap think to check and replace.

Hi Brian. Interested to hear more about this. Especially if you are referring to the quick connect with the wee red push to release tab that connects to engine. My 2016 merc has this fitting

 

[BrianVT]

Hi Brian. Interested to hear more about this. Especially if you are referring to the quick connect with the wee red push to release tab that connects to engine. My 2016 merc has this fitting

Mine is the old, all metal, push/turn type.
But the concept is the same. The inside can get plugged up with crap.
This may not solve the OP's problem but it's wise to check the easy/cheap things first.

 

[QBhoy]

Mine is the old, all metal, push/turn type.
But the concept is the same. The inside can get plugged up with crap.
This may not solve the OP's problem but it's wise to check the easy/cheap things first.

Absolutely. Also have an incline he might be hitting the rpm limiter. Not always obvious when it happens. No beeping as you’d expect. If he is underpropped, might be the case.

 

[oba97]

Start by taking the fuel filter and dumping contents into a clear container to see if there is anything but clean gas. Then check fuel pressure to see if it falls off as you get to WOT. It might be a restriction in the fuel supply side or weak fuel pump

How do you check fuel pressure? I don’t think I have a gauge.

 

[alldodge]

Get a vacuum/fuel pump test gauge, similar to this one
https://www.amazon.com/Hromee-Carbu...P4P97H2/ref=pd_lpo_2?pd_rd_i=B08P4P97H2&psc=1

Disconnect the line between the fuel pump and carbs and place a Tee fitting. Connect gauge to Tee and go for a run

 

[QBhoy]

How do you check fuel pressure? I don’t think I have a gauge.

Did you check you’re not just hitting the rpm limiter ? Sure sounds like it. What rpms does it happen at ? My 2016 merc does exactly what you describe when I have less pitch on the prop. No audible warning. Just gets to it’s max…drops off the rpms…climb to max then same again.

 

[oba97]

Get a vacuum/fuel pump test gauge, similar to this one
https://www.amazon.com/Hromee-Carbu...P4P97H2/ref=pd_lpo_2?pd_rd_i=B08P4P97H2&psc=1

Disconnect the line between the fuel pump and carbs and place a Tee fitting. Connect gauge to Tee and go for a runT

Get a vacuum/fuel pump test gauge, similar to this one
https://www.amazon.com/Hromee-Carbu...P4P97H2/ref=pd_lpo_2?pd_rd_i=B08P4P97H2&psc=1

Disconnect the line between the fuel pump and carbs and place a Tee fitting. Connect gauge to Tee and go for a run

No carbs. My outboard is fuel injected.

 

[oba97]

I was able to get out tonight and try a few things out. The only thing I did before taking the boat out was disconnect the fuel line at the motor then reconnect. I also disconnected the fuel filter then reconnected. I didn’t clean anything at this time, I was just inspecting.

I was able to run at WOT with no issue????? My tach was at ~5600. So who knows…The only thing I can think of is that I added a can of sea foam last time out and that cleaned the injectors or there was some crud that fell out (unnoticed) when I disconnected the lines.

 

[alldodge]

Being injected there should be a shrader valve on the rail to test. Will need a high pressure gauge that goes to at least 100 psi

 

[Texasmark]

Start by taking the fuel filter and dumping contents into a clear container to see if there is anything but clean gas. Then check fuel pressure to see if it falls off as you get to WOT. It might be a restriction in the fuel supply side or weak fuel pump

While you are at it, get a new filter and cut your old one open to see if its clogged. You may be "un" pleasantly surprised at what you might find therein.