How to service Mercury 4 Stroke Outboard FSM Fuel Supply Module

[@jagtds79]

Marine Boat Guy, great video and thanks for sharing! I have a 2009 90hp Merc 4 stroke w/this same FSM. Here’s my issue and what I’ve done so far.... Engine cranks fine, moving around in the 1000-3500/4000 rpm range is fine. If I bury it to wot it bogs down and hangs up around 5k rpms. If I back off to around 4200 you can hear/feel the motor pick up and get to the correct rpm range of that particular position of the throttle (NOT FLY BY WIRE THOUGH). If I ease into the throttle little by little I can get it a little higher in the rpm range than when I bury the throttle, but it will go slightly higher if you ease into it. Dependent on load (passengers/towing a tube) it can be as low as 5000 rpm with a decent load or 5400 with just me in the boat. Here’s what I’ve done....Changed high and low pressure filters, plugs, changed fuel lines from the tank to the motor, added a fuel/water separator and electrically checked the coils and the injectors. From a resistive standpoint there is no deviation between like components. There is no primer bulb. My next test was to put gauges on the fuel lines under the cowl and see what I get. Oh, I also have vessel view and I’ve gotten no warnings, codes or anything from that....I’m just trying to figure out what points at the FSM? there’s 2 pumps and a float. 🤷‍♂️

[@maineboatguy]

You’ll definitely want to hook up a fuel pressure tester to the high pressure test port on the engine and run it while someone watches the gauge to see if you have a loss of pressure. Adding a fuel primer temporarily could help you diagnose it as well, light pressure on the bulb while it is bogging down to see if it picks back up.

[@danielpersa2688]

@jagtds79 I'm having this same issue on my 2014 90HP Merc 4 stroke and done the things you mentioned above. Did you ever find the culprit?

[@jagtds79]

@@danielpersa2688 Yes - Coil pack I swapped a new one in until it went away. Replaced all 4.

[@danielpersa2688]

@@jagtds79 thanks for taking the time to respond after all these years. Appreciate you.

[@jagtds79]

@@danielpersa2688 FWIW, I did replace the float as mentioned 4 yrs ago and that didn't fix it. However, when I replaced the coil packs (Amazon, not OEM) it fixed the problem. The other day though, when I was going out I got a short alarm and Vessel View showed a code (1111-23) Fuel Float switch. Alarm went away and we kept going with no issues. 🤷🏻‍♂ I'll also add that a year ago I got code (1112-23) Fuel Vent Switch alarm and it went away and we kept going with no issues......🤷🏻‍♂

[@GoldenParachuteEnt]

Thank you for making this. I just bought a 2013 75hp 4s EFI with only 50 hrs. It sometimes has really rough idle and stalls or wont move past 2500 rpm WOT. I heard it could be the floater switch.

[@maineboatguy]

K Ramsey yes that's a possibility. Make sure the fuel supply hoses are free and clear, sometimes easiest to try and run the engine off a separate fuel tank to rule out other issues. If you have a primer bulb installed inline you can give it a couple pumps to see if that corrects the issue. I had another one of these that ended up needed a low pressure fuel pump. mercury has a service bulletin out that helps with diagnosing.

[@GoldenParachuteEnt]

@@maineboatguy Do you know where I can find the Bulletins?

[@maineboatguy]

K Ramsey www.marinepartsexpress.com/Merc_Product_Bulletins/Fuel%20Supply%20Module%20FSM%20Troubleshooting%20Bulletin%20No.%202009-09.pdf

[@kipawaoutpost]

I changed the low pressure pump still doing problem Does switch control the pump?

[@bowhunter182]

Sir,great video, I have a 2012 115 hp 4 stroke that is not running right. Has 96 hours on it from new. Starts up and runs fine for 10 minutes or so then starts running rough and shaking and won't stay running. Usually starts right back up .it may run for a little bit then starts acting up again. I have good pressure at the Schrader valve when I depress it in. Could this be my float switch? Do you have the meter set to ohms to check it ? Also,my foam filter was completely gone. I replaced fuel, fuel line, filters,plugs and installed a water separator filter. Any help is greatly appreciated.. Scott

[@maineboatguy]

Are you experiencing those issues only at idle? Can you drive the boat? Check throttle position sensor and idle air control. Could be float switch if it’s overflowing fuel into the air intake. Yes check on ohms setting. Troubleshooting this engine is easiest with diagnostic software unfortunately.

[@bowhunter182]

@@maineboatguy, yes I can drive the boat at times in between when it is acting up. Most of the time o can't get it on plane.it runs for 10 to 15 minutes then o have to shut it down..it starts right back up .but then it won't idle. Could it be the float switch? What is the beat way to do those checks you mentioned? Thanks so much for your help...

[@maineboatguy]

@@bowhunter182 do you have a service Manual for your engine? I suggest finding the correct Mercury service manual so you can perform those tests. Do you have any way to pull the engine trouble codes from the ecu? Would really help to see what the ecu is showing.

[@bowhunter182]

@@maineboatguy ,I will look at the float switch and see if that is the issue. If not I will take it to a service technician and have it looked at. Thank you so much for your help and promptly answering my questions..

[@Tomcoker1952]

Thank you for the video, I have the 75 hp version, and pulled my FMS to check the pumps. Can you tell me where you ordered the rebuild kit with the seals form? Thank you

[@maineboatguy]

Tom Coker sorry I missed your comment, hope you got it all figured out. If not let me know....

[@madelynasbury1508]

Hey Maine Boat Guy. You tested the float switch in your video but apparently got no continuity. Was the switch you tested OK? I've tried testing mine. I get nothing from the meter. No continuity no matter the position of the float. Bad float???? Should get an open or closed continuity, right? Appreciate any help......

[@maineboatguy]

Madelyn Asbury if you’re sure the meter is set up properly it sounds like you have a bad float, best to have a meter that beeps so you know the switch is opening and closing instead of watching the meter. Circuit should be open with float upside down and closed when in upright position. Hope that helps and isn’t more confusing 😂

[@dscopes]

I have a Mercury 6 hp 4 stroke. Fuel is not pumping/moving past the fuel pump into the carb when I pull the starter rope. I put a new fuel pump on and the carb is still dry. Any tips? Many thanks.

[@maineboatguy]

Darryl Scopes can you get fuel past the pump by using the primer bulb in the fuel line? Mercury had some fuel lines that will deteriorate on the inside and clog the lines and inlet valve on carburetor.

[@dscopes]

Maine Boat Guy I’m familiar with what your saying, but I confirm fuel is in the filter, past the lines. Fuel goes into the pump, but not out the top

[@maineboatguy]

Darryl Scopes you said the "carb is dry"? Can you get fuel to the carb with the primer bulb?

[@dscopes]

@@maineboatguy there is no primer bulb

[@maineboatguy]

Darryl Scopes there should be a primer bulb. I'd install one to pump some fuel up to the carb. I've never seen a carbureted outboard start without getting fuel up to the carbs before cranking.

[@claudew5582]

‘13 90hp merc. 4 stroke, first 3 serial 1B6. Motor starting running rough after the 2nd time out, while changing the fuel filters and plugs I noticed 2 things, plugs were wet (gas) and the foam air filter had chunks of foam missing. I heard that mercury replaced the foam filter for disintegration, how do I fix this if the foam pieces were sucked in?

[@maineboatguy]

The chunks of foam will usually get sucked in, pass through the engine and out the exhaust, you can look inside the intake and remove any sensors in the intake to ensure the foam isn’t stuck in a sensor, you may have to remove the entire intake to inspect sensors and fuel injectors. I’ve seen the foam completely gone from the air filter but never effect the running of the engine so if sensors and injectors are clean I don’t think I’d be chasing the foam pieces for long before searching for another issue.

[@claudew5582]

@@maineboatguy Thanks for the information, appreciated.

[@claudew5582]

@@maineboatguy Motor has been at dealership for 3 weeks, the only code was overheat so they replaced the impeller, no more code but motor runs terrible. Did pressure check of cylinder hot and cold all within specs. Pulled fuel rail/ injectors cleaned and tested All test done with fresh fuel to be sure. They suspect, but no sure that it’s a faulty ecm or water getting into #1 cylinder both very expensive.

[@vaughnspence8366]

what did you set your meter to?

[@maineboatguy]

Set to continuity so that it makes an audible beep. At least that's how I do it.

[@mljavabrle]

Hello, I have Mercury 100 EFI 2007 and probably a problem with fuel pressure regulator but I’m not sure and I will appreciate if you could give me your opinion. If engine is running within 2000-5000rpms and I want slow down to a minimum speed usually engine shuts off. Then again I need to turn engine on put in a gear and I can drive with a minimum speed. What can be a problem?

[@maineboatguy]

Paolo Nacinovic a diagnostic computer would eliminate most parts that show values on there. Otherwise I would have the injectors cleaned and fuel system serviced unless you've already done so?

[@mljavabrle]

Maine Boat Guy for me is a problem to find someone with a diagnostic computer in my home town. FSM was already opened, there was plenty of dirt on a small filters that are on pumps and on fuel pressure regulator. Pipe that is connected on fuel pressure regulator was damaged. So I’m sure that both pumps are working fine, and injectors been cleaned afterwards, I can only measure fuel pressure? Also air filter was all falling apart, maybe some piece of filter stuck somewhere and interrupts working of IAC valve?

[@maineboatguy]

Paolo Nacinovic have you checked the throttle position sensor voltage to make sure that is adjusted properly? Also did you leave the fuel pressure tester on the engine when it stalls to see if you actually loose fuel pressure?

[@mljavabrle]

Maine Boat Guy I didn’t check voltage on throttle position sensor. Can you tell me how to properly check or adjust it? Unfortunately I haven’t done fuel pressure test, I hope that I will do it this weekend.

[@maineboatguy]

Paolo Nacinovic you'll need a multi meter and the service manual. Most tps should be set at .7 volts to 1.0 but the service manual will tell you exactly.

[@deejathome]

part 2?

[@maineboatguy]

deejathome I apologize, I haven't uploaded the rest of the video. Not sure what happened but I'll get it asap!

[@deepseadeepsea7243]

Hello, I find a lot of gasoline in my engine oil I HAVE A MERCURY VERADO 300 HP 6 L CAN HELLP ME

[@heraclez7750]

volume too low dude

[@RICHJMS]

Flip that float switch over again!!!!