No power after half throttle on port motor. Mercury horizon 2001

DarrenC

Member
Jul 10, 2018
161
Boat Info
2001 Sea Ray Sedan Bridge 400
Engines
Mercruiser horizons 350
this is now the second season with no answers yet. My port motor gets up to 3.9 at half throttle and same with starboard motor. When I give more throttle starboard motor goes up over 5.5 rpm giving outstanding power and port motor gives nothing more. After a while it will increase slightly as it’s working off the other motor it seems. Things I’ve done so far. Checked timing by a professional, replaced fuel pump. Checked all cylinders doing a compression test and fantastic compression. She throttles up in neutral no problem it’s when it’s under way. Would anyone have any idea what it could be the restriction? I’ve even took off props and sent them out to be checked and cleaned and tuned up, could it be a fuel restriction? Any help from anyone that had this in the past would be sincerely appreciated. I’m racking my brain. Thanks
 
Fuel injected MPI sorry
 
Why was the fuel pump changed out?
Do you know what your fuel pressure is on the rail? If it is 40-43 pi at load, then I would move to the fuel injectors next. If not, then I'd start with the easy restrictions, like the fuel water separator, and fuel shutoff solenoids. Any sounds of missing at idle or at load?
If you want a real fun read, grab a beer or three, and read this:
http://clubsearay.com/index.php?posts/1061202/
A work in progress.
 
Why was the fuel pump changed out?
Do you know what your fuel pressure is on the rail? If it is 40-43 pi at load, then I would move to the fuel injectors next. If not, then I'd start with the easy restrictions, like the fuel water separator, and fuel shutoff solenoids. Any sounds of missing at idle or at load?
If you want a real fun read, grab a beer or three, and read this:
http://clubsearay.com/index.php?posts/1061202/
A work in progress.
Why was the fuel pump changed out?
Do you know what your fuel pressure is on the rail? If it is 40-43 pi at load, then I would move to the fuel injectors next. If not, then I'd start with the easy restrictions, like the fuel water separator, and fuel shutoff solenoids. Any sounds of missing at idle or at load?
If you want a real fun read, grab a beer or three, and read this:
http://clubsearay.com/index.php?posts/1061202/
A work in progress.
 
The water Separator filter was changed last year and this year. We did a fuel compression test at the rail and if I remember correctly it was going up to 20 psi that it wasn’t holding it was dropping to zero so we changed the fuel pump. The fuel pressure had remain the same and was told by another mechanic that the fuel pressure was good. When you say Testing under load do you mean checking fuel pressure while the boat is Under way? Is there a way to check the fuel injectors?
 
Boat runs perfect at idle in under load until I try to increase over half throttle on port motor it simply does nothing at all and seems to bog a little.
 
The water Separator filter was changed last year and this year. We did a fuel compression test at the rail and if I remember correctly it was going up to 20 psi that it wasn’t holding it was dropping to zero so we changed the fuel pump. The fuel pressure had remain the same and was told by another mechanic that the fuel pressure was good. When you say Testing under load do you mean checking fuel pressure while the boat is Under way? Is there a way to check the fuel injectors?
I'm going to make minimal comments because by 2001, you could be running a smart enough fuel injection system to let you test injectors with a scan tool or other device. That other thread I pointed out is mine, and is about 5 pages deep now. Bigger boat, older engines, perhaps a shadier past, but basically having the same issue (among others). The smart guys will be showing up soon to help you diagnose.
If you know your engine's serial number, posting that can help take a lot of guesswork out of what you are working on.
Good luck.
 
What do you mean “compression test at the rail”?

Sound like a fuel pressure test.

Two things I would do first:

1. fuel pressure test under load.
This will require a pressure gauge and possibly a helper.
Record the fuel pressure, especially when the engine isn’t running well.

2. A properly performed compression test, both wet and dry. If this was done already, can you post the results?
 
Engine serial # OL670519
Engine serial # OL671965
 
when fuel pump was changed did they change out as a complete assembly or just the pump?? Make sure the fuel pressure regulator was changed as well. Without a good regulator pressure will never be enough. Been there twice.
 
when fuel pump was changed did they change out as a complete assembly or just the pump?? Make sure the fuel pressure regulator was changed as well. Without a good regulator pressure will never be enough. Been there twice.
 
Yes the entire assembly was replaced just to be sure. I’m stumped and can’t figure out if it is a sensor or fuel issue
 
I agree with scoflaw. I had a 2002 310DA with the same problem. Turned out to be two bad injectors on the port engine.
 
I agree with scoflaw. I had a 2002 310DA with the same problem. Turned out to be two bad injectors on the port engine.
Was there a way to test them or did you just replace them all? If so did you use OEM injectors or aftermarket? I’m going to change the injectors this weekend and praying that is the issue.
 
Was there a way to test them or did you just replace them all? If so did you use OEM injectors or aftermarket? I’m going to change the injectors this weekend and praying that is the issue.
I replaced only two that were bad (literally broken wires). The Mercruiser scan tool has a feature that allows for injector testing. Without it, you can try to feel or listen to each of them. They make a clicking sound if they are opening and closing. You may be able to feel them with your fingertip, or place a screwdriver on them and your ear on the handle of the screwdriver to listen. If they are opening and closing, but are not spraying cleanly, that would be hard to diagnose without sending them out for service. OEM injectors are expensive, but I was in a rush for time and they were immediately available to me. There are shops that clean them for comparably short money, depending on where you live, there may be a place nearby you to send them. Those places generally have decent turnaround times.
 
If your fuel lines and injectors are 18 years old, they're overdo for a replacement on the lines and at a minimum have the injectors serviced

I can't speak to the injectors, but the fuel line at 18yrs is end of life. Even on an A1 rated hose, ethanol deteriorates the hose from the inside, looks fine outside, but under pressure - ie high RPM loads - the fuel line starts collapsing on the inside. Had this happen on my 185, over about 3500rpm it started surging and would seem to run out of gas. After a short period it would start up and run fine but the cycle would repeat. Was shocked to see the condition of the inside of the fuel line. I was also seeing debris from the hose in my fuel filter. Replaced hose / filter, problem solved. If replacing the fuel line is hard on your boat, I would run a portable tank to confirm or eliminate a fuel tank / feed problem.
 
I can't speak to the injectors, but the fuel line at 18yrs is end of life. Even on an A1 rated hose, ethanol deteriorates the hose from the inside, looks fine outside, but under pressure - ie high RPM loads - the fuel line starts collapsing on the inside. Had this happen on my 185, over about 3500rpm it started surging and would seem to run out of gas. After a short period it would start up and run fine but the cycle would repeat. Was shocked to see the condition of the inside of the fuel line. I was also seeing debris from the hose in my fuel filter. Replaced hose / filter, problem solved. If replacing the fuel line is hard on your boat, I would run a portable tank to confirm or eliminate a fuel tank / feed problem.
I would guess I would have to do it under load while driving correct? Because she throttles up in neutral and runs great.
 

Forum statistics

Threads
112,950
Messages
1,422,862
Members
60,932
Latest member
juliediane
Back
Top