Optimax with air in the fuel rail

**Narcoholic** · 08-07-2020, 01:20 PM

I have an 06 175 hp opti. I purchased the boat at a pretty decent deal as it had been sitting for quite some time. Here is a list of what i did. Took off vst replaced all fuel pumps, even the small one behind it. New Plugs water pump , trim pump, drained entire fuel tank, cables sc1000 gauges etc etc etc. Motor was running fine. I was having a issue with the other motor, so i took it to the ramp put it in the water left it idling for 10 mins. Got in to take it out the one motor with no issues shuts off , wont start back up. Take it home. Spray starting fluid in it starts right up. Push in shrader valve with just the key on and clear air out of system. Retry to start it and LOTS of air in the rail now. I put a clear hose to it with air chuck and get lots of air. Turn the key on and off clear air out try to start again wont start check shrader and LOTS of air again. I pulled left and right diaphragms and see no holes or cuts I have no fuel in the air side. The other motor I was having issues with would idle great rev up at dock but under load would run out of fuel before getting on a plane the primer bulb was not flattened and I replaced all fuel lines to the motor from tank as well and no anti siphon valve on tank i checked. I took injectors air and fuel to be cleaned, flowed and tested
. They were dirty I have not been able to test if that problem is fixed yet, because the other motor just decided to quit. So i have numerous issues I know.

Question is for the motor that wont start. How does a lot of air get in the fuel rail ? Also when pulling Fuel diaphragm I did not find it hard to install it by hand. People on the web talk about some 90lb heavy duty spring. Mine was not that hard to do by hand I did not need a tool. Did that spring lose pressure all of a sudden ?

Obviously could use any help, Ant is much appreciated.

**XstreamVking** · 08-07-2020, 01:54 PM

There is a priming procedure for the dual fuel pump opti's. Hit the primer bulb, turn the key on for a few secs. then back off. Do this several times to prime the system.

**Narcoholic** · 08-07-2020, 03:19 PM

Yep did that numerous times. So I went to Oreilys and got a pressure gauge put it on the air side and got 80 psi using starting fluid. Then the motor started running by itself i quickly added water to it and it ran for maybe 2min. Then it quit along with a lost coms fault. I put the fuel pressure gauge on the fuel side and squirted out lots of pure air then some fuel . Went back to turn key on run pump, off then on until pure fuel came out. Tried to start it got nothing. Used starting fluid got it running only using starting fluid, pressure only came up to 86 psi. So I assume because I dont have the 10 psi difference the motor wont run. My question , is that because of all the air from some where. It is a new pump. Where is all this air coming from. The pump can't be making pressure with all that air.

**nitro_rat** · 08-07-2020, 03:34 PM

In an Opti fuel is injected into a pressurized chamber of air before being injected into the cylinder. If the fuel pressure isn't 10 psi greater than the air pressure air backs up into the fuel rail when the fuel injector opens. So your air leak is the injectors due to inadequate fuel pressure.

Mercury makes a neat dual gauge tester with clear hose so you can check air and fuel pressure simultaneously and actually see the air backing up into the fuel system as it's happening. Probably about a grand for that setup. That's why I don't work on Optis...

**InjectorService** · 08-07-2020, 04:35 PM

Just go grab 2 fuel injection pressure gauges from Harbor Freight or something. Air should be 80psi, fuel should be 90. Watch them at the same time. Have a friend key it on, the fuel should prime up, and once he starts cranking the air should start catching up to the fuel at which point they would be at 80 & 90. I think Nitro hit it on the head for sure.

EDIT: Did I read that right that the fuel pump is new, or were you talking about something else? If so which pump(s) were replaced. Could be a weak fuel pressure spring too. Maybe swap springs & diaphragms, or complete rails from one motor to the other?

**Narcoholic** · 08-07-2020, 05:06 PM

Thank you SO MUCH. I did not understand how or why the air would get in rail. New pump will be getting returned for a another new one. Again i can't thank you enough. Between the two of these mercs I have been going nuts. The easiest of tasks were not going easy like they used to. Have a great weekend to all Thank You

**Motv18** · 08-10-2020, 04:46 PM

Air can get in through the fuel regulator or diaphragm.

leek down the fuel side get the pressure up and watch it drop to 14-20psi if it goes under 14 you have a leak. In the injector, regulator, diaphragm or various o rings that seal the injectors in the rail.

**Narcoholic** · 08-15-2020, 12:00 PM

Well i replaced the high pressure pump with a Walboro and the motor started right up. i took it to the ramp and now BOTH motors wont go over 1800 rpms without breaking up. the port which i was having the fuel issues with will die out like its still losing fuel but will start right back up with choke the primer bulbs are fine . The starboard never shuts off but wont rev up. UGHHHH I'm so sick of these motors.

**Narcoholic** · 08-15-2020, 12:20 PM

I have a question. I did not think this was an issue but the only alarms on both the motors say the oil is at 98%. Would that put me in safe mode ? Both side tanks are full to the top and both tanks below have about a 1/4 tank in them . I have not messed with them since I purchased this boat. I don't know what kind of oil is in them,but by color it looks like walmart super tec oil really blue.

**racer** · 08-16-2020, 08:55 AM

I dont work on many of these but have you verified the computer knows they are in gear? Yes oil codes will but the engine into self protect/safe.

**Narcoholic** · 08-16-2020, 10:40 AM

How do I check to know if the computer knows they are in gear ? I know the yellow wires to the throttles are not hooked up and the motors can be started in gear.

**Euroski** · 08-16-2020, 10:45 AM

my 300xs wouldn't go above about 2K if wasn't in gear

**Narcoholic** · 08-16-2020, 12:18 PM

Ok so I pulled the lower cowl and looked at the switch on the selector and it does go in and out. Past knowing that the switch is moving and not stuck is there a way to check that the switch is working ? Also I re checked oil in the side fill tank and it is to the top but the alarm saying 95% oil is still going off. I checked the two blue wires for continuity and they have none. Not sure what this means if anything.

**Narcoholic** · 08-16-2020, 12:20 PM

I'm not being able to go above 2k in gear and moving. I have rev'd the motors up in neutral and they dont go above 3000-3500 and the alarm goes off about over rpm.

**Narcoholic** · 08-16-2020, 02:03 PM

OK,,,,,,, So i made a loop between the two blue wires on both motors on the oil reserves. Took it to the ramp and no more oil alarm and the motors have full power. OMG!!!!! I can't thank you guys enough. I owe people drinks or food. HUGE weight has been lifted from my brain. All the other problems i was having were driving me just nuts. To know that this could be the light at the end of the tunnel is AMAZING. I might actually get to use this thing before the end of the season. Now to find oil tank. I will update when i get new tanks installed. Again THANK YOU GUYS