2006 merc 40 4 stroke

[longeze]

Each time I take my boat out it runs great for the first 35 mins. After I throttle back and idle around it starts to want to stall out. If it does and I restart it idles fine for 5 mins then same issue. Changed tank fuel line and connectors, fuel filters, oil/filter, plugs. Can the idle air control solenoid cause this issue after 35 mins? Once this issue pops up I can't get it up to speed again. Only idle speed.

 

[Jeff J]

Have you tried pumping the primer bulb to see if that brings power back?

 

[longeze]

Have you tried pumping the primer bulb to see if that brings power back?

I have, no difference. Seems the bulb is always soft. I replaced the the fuel pump. Also the fuel line from the tank. It runs fine with the cowling off I found out. Guess something is breaking down. Coils? Idle control valve? Might replace them next.

 

[Jeff J]

Idle control valve issues I have seen only affect idle. There is one on a 150 hp in the fleet I clean twice a season.

Coils could be breaking down and causing problem when warmed up.

Anything electrical can have heat related failures.

Assuming it’s an EFI, the high pressure fuel pump comes to mind too. Do you have a way to monitor fuel rail pressure? Pumping the primer bulb would not necessarily provide enough pressure for the injection system to work.

I don’t have a manual for this size Mercury… yet. May have to get one for the same vintage 50 I have in the shop.

 

[longeze]

Idle control valve issues I have seen only affect idle. There is one on a 150 hp in the fleet I clean twice a season.

Coils could be breaking down and causing problem when warmed up.

Anything electrical can have heat related failures.

Assuming it’s an EFI, the high pressure fuel pump comes to mind too. Do you have a way to monitor fuel rail pressure? Pumping the primer bulb would not necessarily provide enough pressure for the injection system to work.

I don’t have a manual for this size Mercury… yet. May have to get one for the same vintage 50 I have in the shop.

Thanks for the ideas. I'm gonna try and replace the lower spark plug. 3 cyl. Couldn't get to it without removing the coils. When the issue happens I can't bring the power up. Idle only and it breaks up every 20 seconds then idles ok and I have to work the throttle. I limp home. Yesterday I took the cowl off and it worked ok to get back. Trial and error I guess. I have a meter, I might meter the coils.

 

[Jeff J]

A cautionary tale about spark plugs. My Yamaha ran me in circles a couple of years ago. Plugs spark tested okay on the boat so I kept looking. I finally circled back to spark plugs but put them on a tester with a pressure chamber. One quit firing as soon as the pressure got to 5 psi. I spent around $300 before figuring out all I needed was an $8 spark plug.

 

[longeze]

A cautionary tale about spark plugs. My Yamaha ran me in circles a couple of years ago. Plugs spark tested okay on the boat so I kept looking. I finally circled back to spark plugs but put them on a tester with a pressure chamber. One quit firing as soon as the pressure got to 5 psi. I spent around $300 before figuring out all I needed was an $8 spark plug.

Wow I was thinking that today. It was running fine last year. I changed the plugs did a oil change. Well I got to the third plug and changed it. Took it for a ride and fine for about 35 mins. So took the cowl off and ran fine going home. I felt the voltage regulator and burned my finger. I ordered a new one. It will be here tomorrow. I'll let you know. If that doesn't fix it I'll change the plugs again. Then coils.

 

[longeze]

Well I replaced the voltage regulator. No good. Took the cover off and drove home 40 mins. Took the thermostat off and it tested fine. What else? The Electronic control assy? I didn't replace the coils yet. Man runs so good with the cover off. Thinking about making a nice scoop on the front. Lol

 

[racerone]

Is a plug wire shorting to the cowling ?----Cowling does not suddenly need to let in more air after all these years I think.

 

[longeze]

Is a plug wire shorting to the cowling ?----Cowling does not suddenly need to let in more air after all these years I think.

I checked that. Nothing shorting.

 

[boscoe99]

Well I replaced the voltage regulator. No good. Took the cover off and drove home 40 mins. Took the thermostat off and it tested fine. What else? The Electronic control assy? I didn't replace the coils yet. Man runs so good with the cover off. Thinking about making a nice scoop on the front. Lol

What does a voltage regulator have to do with ignition?

 

[boscoe99]

Is the engine serial number not known?

 

[airshot]

Wasp or bees nest in cowling vents ? When installing cowel does it push on any wires to create a short ? Does it pinch a fuel line ?

 

[longeze]

Is the engine serial number not known?

1c015210

 

[longeze]

Wasp or bees nest in cowling vents ? When installing cowel does it push on any wires to create a short ? Does it pinch a fuel line ?

Not that I can see. Nothing pinched.

 

[longeze]

What does a voltage regulator have to do with ignition?

With the cowling off I burnt my finger on it. About the same time the garmin gps shut off. So the new one still gets hot. I saw a post on line with symptoms of a bad voltage regulator and one was a rough running engine.

 

[longeze]

Well I'll change the high pressure pump and check the screen when I get it back to NJ. I took it out of the water and put the travel cover on it.
I'm just shooting from the hip without proper test equipment. Frustrating. Thank you all for the ideas. This is a great site. When I finally fix it I will be sure to let the group know. Much appreciated.

 

[Jeff J]

I think buy a basic fuel injection test kit for ~$45 before spending $600 on a high pressure fuel pump that may or may not be needed.

Basic Fuel Injection Service Kit

Amazing deals on this Fuel Injection Service Kit at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

 

[longeze]

I think buy a basic fuel injection test kit for ~$45 before spending $600 on a high pressure fuel pump that may or may not be needed.

Basic Fuel Injection Service Kit

Amazing deals on this Fuel Injection Service Kit at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

I think buy a basic fuel injection test kit for ~$45 before spending $600 on a high pressure fuel pump that may or may not be needed.

Basic Fuel Injection Service Kit

Amazing deals on this Fuel Injection Service Kit at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

Great idea. Thanks!

 

[longeze]

Has anyone ever had an exhaust leak? Was wondering if it's possible for a leak to build up inside the cowling and cause it to lose power, then with the cowling off it runs fine ? Ever hear of it?