5.0 MPI surging and bogging down at cruise speed

[metsfan3197843]

5.0 MPI with bravo 3 OM656133

last trip out after getting up on step, (3400 RPM) my engine started surging and slowly bogging down/loosing RPM’s. Ran fine at lower speeds, we even trolled our way back to the dock. I was able to repeat the problem 4 or 5 times. I had my scan tool with me but nothing was jumping around besides fuel usage. I figured I had water in the fuel but when I got home and pulled the filter, not a drop. Hooked up the fuel gauge at got 35 psi and held when pump shut off and raised around 5 psi when the vacuum line was removed from the regulator. Got a replacement inline filter coming. Not sure where else to look. Any thoughts?

Thanks

 

[achris]

The scantool has limited application for diagnostics. It can't show, for example, the realtime sensor reads. If you have a sensor failing, that could account for your symptoms, but without the diagnostic software running, you're all just guessing.

One thing worth doing it replacing the spark plugs... Beyond that, you'll need the software to at least rule out other things.

Chris...

 

[Searay240sd]

Keep the fuel pressure gauge hooked up and take boat for a ride. Keep an eye on the gauge when the motor starts to act up.

 

[metsfan3197843]

Hmm I was told by the Rinda salesman on the phone that the tool could see every parameter that the software can. I actually wanted to buy the software and he talked me into buying the cheaper option, the scan tool

 

[wellcraft-classic210]

Running & recreating the problem with the fuel pressure gauge hooked up would verify a pressure issue -- If you find that you might want to inspect your check valve oa the fuel tank exit ( typically a barbed fitting where the rubber line meets the tanks.

Debris can get caught and limit fuel flow -- only drops pressure under high demand & could cause symptoms as you described --

 

[tpenfield]

Seeing every parameter vs. doing something with every parameter is the difference between the scan tool and the software.

Maybe Rinda will let you trade up to the software, since they may have sold you short on the expectations.

 

[metsfan3197843]

I replaced the inline fuel filter on the upstream side of my fuel pump, the contents were pretty nasty. This boat is new to me and I'm not sure when it was changed last, if ever. I attempted to check the anti siphon valve but the fittings are corroded and feel like they want to strip so I have not had that apart. Took it out on the water and had both the scan tool and the fuel pressure gauge hooked to the fuel rail. Had 35 psi on start up and rose a couple of pounds on acceleration. Once on step and at around 3200-3400 RPM fuel pressure would slowly start to drop to around 15 psi and the engine would dog down. Nothing abnormal on any parameters on the scan tool. was not going into guardian mode and all sensors reading good. Looked to be completely fuel related. I've had this boat out around a dozen times since I've owned it and last time out was the first time I've had this issue. I remembered that I had run the kicker on the trailer in the driveway the day before the issue started so last night for grins I again ran the kicker, a 9HP Mercury 4 stroke. The day I ran it in the drive I opened the ball valve just upstream of the priming bulb and had to prime it for a long time before I got the line filled. I only bring this up because after running the kicker last night, all my main engine fuel issues went away. After shutting down the kicker and closing the ball valve I tried the main again and got to wide open throttle no problems. Cruised around for a bit and shut off the engine and repeated multiple times. I'm convinced my issue has something to do with my kickers fuel plumbing but can't make it make sense.

My fuel system consists of the main fuel tank pick up, anti siphon fitting that goes to an inline filter. Out of the inline the line T's with one line going to the Mercruiser fuel pump/water seperator skid and the other running to the kicker with a ball valve just before the priming pump. Is this plumbed incorrectly?

Hope all that makes sense......

 

[Searay240sd]

What year is the boat? Does it have cool fuel 3 module. Did you see any paint when you check the filter? Did you also replace the mesh screen below the canister filter?

 

[scoflaw]

What year is the boat? Does it have cool fuel 3 module. Did you see any paint when you check the filter? Did you also replace the mesh screen below the canister filter?

To make a point about the CF3, which the OP probably doesn't have, the paint chips don't show up in the filter, they are down stream of that. You will see them on the fuel pressure regulator, which is bolted to that module.

 

[metsfan3197843]

It is a 2004 Trophy Pro 2359. I don’t believe I have the cool fuel 3 but to be honest I’m not sure what I have. The engine compartment is so frigging tight you can’t see what goes where.....

 

[achris]

It is a 2004 Trophy Pro 2359. I don’t believe I have the cool fuel 3 but to be honest I’m not sure what I have. The engine compartment is so frigging tight you can’t see what goes where.....

Doesn't matter what the boat is... All we need the engine information and serial number... That's what tells us what it is... Boat makers, all of them, don't make the engines. They just buy them from one of a few suppliers (mainly 2, Merc and Volvo, who mainly use GM long block engines) and install them. Often not even install them, they leave that to the shop/dealer selling the boat. So telling use the boat is of no consequence, it tells us nothing. You gave us the engine and serial number right at the beginning, top line of the first post... EXCELLENT. :thumb:

But the tight engine compartment is becoming a standard for boats... It's annoying when you're doing your own work, and expensive if you have a shop do it... But, buyers want more 'people room', so engine rooms have to get smaller,

Chris.........

 

[metsfan3197843]

Gotcha I was just responding to post #8 asking what year the boat was

 

[metsfan3197843]

What is common practice on the fuel supply to the kicker. Do most people tee off the main motor supply line or run a separate line from tank to kicker?

 

[achris]

Gotcha I was just responding to post #8 asking what year the boat was

I think he didn't read the opening post (where you gave the serial number), and was asking for the year of the engine... Most people think of boats and engines the same way as cars. The year of the car IS the year of the engine... Boats, not always true. (Read the boat description in my signature :facepalm: )

What is common practice on the fuel supply to the kicker. Do most people tee off the main motor supply line or run a separate line from tank to kicker?

As most 'kickers' are 2 strokes, and I/Os are 4 strokes, then no, it's usually a separate tank.

If I was using a 4 stroke auxiliary engine, I would probably tee off the main tank, but I would ensure I had absolutely isolation when on the main engine, ie, a 1/4 turn valve, AND a check valve so fuel/air couldn't be dragged back into the main engine supply line. Overkill? probably... But that's me.

Chris.......

 

[alldodge]

replaced the inline fuel filter on the upstream side of my fuel pump

Looks like you have one of the few motors which used the upstream filter. They only used it for a few before doing away with it

https://www.mercruiserparts.com/bam/subassembly/31849/8093/80

9HP Mercury 4 stroke. The day I ran it in the drive I opened the ball valve just upstream of the priming bulb and had to prime it for a long time before I got the line filled. I only bring this up because after running the kicker last night, all my main engine fuel issues went away.

Having the ball valve for the kicker was a good move. Maybe the valve was not fully closed so it was sucking the fuel from the kicker side. Having to take some ball squeezing to fill would lean me in that direstion something was not sealed.

You may have fixed your main issue

 

[Scott Danforth]

and that is why I recommend two separate fuel pickups in a tank vs any tee. if you use a tee, you really need to use a pair of check valves to prevent the main motor from pulling air from the kicker and visa versa.

the little rubber flapper valves in a primer bulb are not sufficient enough of a check valve to prevent this from happening again in the future.

 

[metsfan3197843]

Yup I agree with separation. I’m planning on pulling the drive and motor this fall and completely going through everything and will make the fix then. Thanks everyone for your advice and suggestions