2006 Optimax 150 Surging at 3000 RPM

[spilman]

Engine starts and runs fine until I try to get up on plane. At about 3000 RPM, the engine drops back to 2000 RPM and then surges back to 3000 RPM two or three times until it will quit. The fuel pressure runs at 90 psi and drops back to 80 psi as the engine looses rpm's. Does this sound like the tracker valve?? We have checked fuel pumps and even swapped computers from one engine to another.

 

[Faztbullet]

Re: 2006 Optimax 150 Surging at 3000 RPM

Whats your air pressure???

 

[spilman]

Re: 2006 Optimax 150 Surging at 3000 RPM

Whats your air pressure???

Air pressure stays constant at 80 psi.

 

[jeffersondodson561]

Re: 2006 Optimax 150 Surging at 3000 RPM

What about the boost pump pressure (along side the VST), fuel restriction to vapor seperator? What fuel pumps did you replace? Does not sound like a tracker valve problem, the tracker valve primarily just protects against spikes in pressure from the air and fuel differentials. If your fuel pressure is staying constant at 80 psi when your having the problems I would suspect a fuel delivery to the VST problem. I would also check the vent from the VST #10 for a restriction or possible overflow of gas.

 

[spilman]

Re: 2006 Optimax 150 Surging at 3000 RPM

What about the boost pump pressure (along side the VST), fuel restriction to vapor seperator? What fuel pumps did you replace? Does not sound like a tracker valve problem, the tracker valve primarily just protects against spikes in pressure from the air and fuel differentials. If your fuel pressure is staying constant at 80 psi when your having the problems I would suspect a fuel delivery to the VST problem. I would also check the vent from the VST #10 for a restriction or possible overflow of gas.

I have two engines on the boat. We took the VST off of the other engine, which runs good, and put it on this engine and still has the same problem. The fuel pressure drops to 80 and then surges back up to 90, then back to 80. Could a small leak in the diaphram cause this problem? I'm afraid the only other thing could be the fuel regulator in the port fuel rail.

 

[brandon110]

Re: 2006 Optimax 150 Surging at 3000 RPM

if the med preussure fuel pump is bad the motor will drop rpms to 2300 ish that is the pump next to the VST. you test this by using what merc calls the "touch test" after running the engine while it is failing touch the brass fitting at the top of the pump if it is hot the med prussure fuel pump is bad. is this system there is 3 fuel pumps a pick up pump (diaphram pump) the med pressure fuel pump and the high pressure fuel pump in the vst. i would highly doubt this is a tracker valve issue. i have only seen one tracker valve fail. it got a rip in it and leaked fuel into the air system and the motor ran super rich. I have aslo seen this same issue that you talk about with clogged filters on the high pressure fuel pump in the vst tank more common of a problem with yamahas HPDI system due to the filter on the high presure fuel pump is much finer. hope this helps

 

[spilman]

Re: 2006 Optimax 150 Surging at 3000 RPM

if the med preussure fuel pump is bad the motor will drop rpms to 2300 ish that is the pump next to the VST. you test this by using what merc calls the "touch test" after running the engine while it is failing touch the brass fitting at the top of the pump if it is hot the med prussure fuel pump is bad. is this system there is 3 fuel pumps a pick up pump (diaphram pump) the med pressure fuel pump and the high pressure fuel pump in the vst. i would highly doubt this is a tracker valve issue. i have only seen one tracker valve fail. it got a rip in it and leaked fuel into the air system and the motor ran super rich. I have aslo seen this same issue that you talk about with clogged filters on the high pressure fuel pump in the vst tank more common of a problem with yamahas HPDI system due to the filter on the high presure fuel pump is much finer. hope this helps

We swapped the VST with the med and high pressure pumps intact from one motor to the other. I think this would eliminate these pumps. We did not swap the pick-up pump. However, we did squeze the fuel primer ball constantly to ensure that there was a constant supply of fuel to VST and the motor still stumbles and will not continue to run above 3000 rpm. Could it be the relay that powers the high speed pump is intermittent. We did change out the computers from on engine to the other and still did not resolve the issue. To make matter worse the boat is in the Bahamas and I live in Florida. If I had the boat in FL I would of had it to a dealer long ago. I really appreciate your responses, I am looking at any possibility at this point and need to start replacing things until we find it. I'm just trying to start with the most logical and least expensive part first.

 

[jeffersondodson561]

Re: 2006 Optimax 150 Surging at 3000 RPM

Could a small leak in the diaphram cause this problem? I'm afraid the only other thing could be the fuel regulator in the port fuel rail.

Yeah potentially it could, but did you remove that vent hose (10) with the VST. If I remember correctly that hose vents to the starboard side. If you took that hose off while swapping VST's and put it on the other VST, if that is the problem it could cause the same runablity. How long does it take to loose rpm. If you are priming the bulb and it stayed firm to the point where you could not pump any more, that would pretty much eliminate a fuel restriction. What happens if you stop the engine and key up, when the fuel pressurizes the rail what does the pressure get to and hold at and for how long? Did you ever have any fuel contaminents?

 

[brandon110]

Re: 2006 Optimax 150 Surging at 3000 RPM

do the engines use the same fuel tank? or do they have there own?

 

[Faztbullet]

Re: 2006 Optimax 150 Surging at 3000 RPM

Whats your battery voltage on engine running?

 

[spilman]

Re: 2006 Optimax 150 Surging at 3000 RPM

I believe the vent hose #10 goes to the black air breather cover that sits on the engine. We left this hose on the VST so it was changed when the fuel pumps were changed.
The engine drops RPM almost immediately as the engine reaches 3000 +- RPM the voltage is 14.2 +-.
Once in a while the engine will actually run perfectly for up to 15 seconds and then go back into the same surging mode.
I think the fuel pressure went up to 35 psi or so when you turn the key on but don't crank the engine.

 

[spilman]

Re: 2006 Optimax 150 Surging at 3000 RPM

The engines run off of the same tank, both have water seps. We swapped the fuel lines and it didn't help.

 

[Faztbullet]

Re: 2006 Optimax 150 Surging at 3000 RPM

Sounds like you eliminated the fuel system, it could possibly be a bad TPS sensor that is failing in that particular range....

 

[spilman]

Re: 2006 Optimax 150 Surging at 3000 RPM

I switched the throttle position sensor from good engine to bad engine and it didn't help. It seems that the next easiest part to try is the tracker valve.

 

[jeffersondodson561]

Re: 2006 Optimax 150 Surging at 3000 RPM

Yeah I would try the tracker valve first. If that does not fix it and you move on to the fuel pressure regulator be careful, merc makes a special tool for this that braces it against the rail because of the pressure, you could easily strip out the threads on the rail or worse. (This is what I love about this forum, it makes you dig a little bit in the service information and everybody learns). I am a little unclear about this but I think you have to replace the port fuel/air rail if fuel pressure regulator is bad?

 

[spilman]

Re: 2006 Optimax 150 Surging at 3000 RPM

The forum has been great and I sincerely appreciate all that have taken their time and offered suggestions.

 

[spilman]

Re: 2006 Optimax 150 Surging at 3000 RPM

Changed out diaphram in the starboard fuel rail and still won't run. Does anyone know if the fuel flow regulator in the port fuel rail can be repaired????. Are there any aftermarket fuel rails out there. We are going to swap fuel rails from other engine and see if that is it. I really don't know what else to do.
Thanks.

 

[jerryjerry05]

Re: 2006 Optimax 150 Surging at 3000 RPM

The regulator on my 225EFI a part that EVERYONE said wouldn't go bad,was bad.I did everything twice before following my instincts and change it.
Ran great after that.
Not sure this helps but test the pressure.Any variation?Change it or swap it with the other one.J

 

[spilman]

Re: 2006 Optimax 150 Surging at 3000 RPM

Jerry,
I live in Vero Beach, call me if you get a chance at 473-2430. Lynn

 

[jeffersondodson561]

Re: 2006 Optimax 150 Surging at 3000 RPM

I think you have to purchase the rail

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