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  1. #1
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    Mercury 115 EFI 4 Stroke Stalling

    Mercury 2002, 115 ELPT 4S, Serial# OT552866, Max RPM 5600 to 5800, best I can tell by gauge idles around 650 to 700 RPM, fuel injected 4 stroke

    260 hours on motor, sent injectors to European Marine for service Dec. 2014 and have put on about 100 hours (around 20 hours annually) after injector cleaning, new spark plugs, thermostat, in-line Racor 120-10 micron filter replaced annually, factory under the cowling filter cleaned annually. Have never found any debris or water in filters. Do run Mercury Quickare with all gas and at times have used SeaFoam. I've read several things in regard to primer bulbs on this motor, i.e., yes/no. Don't know if this would matter but the fuel line has been replaced and does have a primer bulb same as original set up.

    Issue: starts right up and idles fine, will troll at idle fine, runs through RPMs without a miss clear up to WOT. When trailering boat and back off throttle into neutral as starting on to trailer motor stalls/dies. Will start right back up instantly. Put into gear and give it a little throttle and back off again into neutral dies. Creates quite the challenge when trailing in the wind. If you back off throttle slowly like coming off of WOT it doesn't appear to have near the problem. Any thoughts appreciated. Thanks
    Last edited by Shotgun1; 08-30-2021 at 05:25 PM.

  2. Member Extremeboating's Avatar
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    #2
    Quote Originally Posted by Shotgun1 View Post
    Mercury 2002, 115 ELPT 4S, Serial# OT552866, Max RPM 5600 to 5800, best I can tell by gauge idles around 650 to 700 RPM, fuel injected 4 stroke

    260 hours on motor, sent injectors to European Marine for service Dec. 2014 and have put on about 100 hours (around 20 hours annually) after injector cleaning, new spark plugs, thermostat, in-line Racor 120-10 micron filter replaced annually, factory under the cowling filter cleaned annually. Have never found any debris or water in filters. Do run Mercury Quickare with all gas and at times have used SeaFoam. I've read several things in regard to primer bulbs on this motor, i.e., yes/no. Don't know if this would matter but the fuel line has been replaced and does have a primer bulb same as original set up.

    Issue: starts right up and idles fine, will troll at idle fine, runs through RPMs without a miss clear up to WOT. When trailering boat and back off throttle into neutral as starting on to trailer motor stalls/dies. Will start right back up instantly. Put into gear and give it a little throttle and back off again into neutral dies. Creates quite the challenge when trailing in the wind. If you back off throttle slowly like coming off of WOT it doesn't appear to have near the problem. Any thoughts appreciated. Thanks
    This is a really stupid question, but are you starting the engine without running water through it?
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  3. Member
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    #3
    No, it's happening when I'm on the water. In the eight years I've owned the boat I've replaced the pump a couple times. If running it out of the water, I'll just idle it with muffs on it.

  4. Member Extremeboating's Avatar
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    #4
    Quote Originally Posted by Shotgun1 View Post
    No, it's happening when I'm on the water. In the eight years I've owned the boat I've replaced the pump a couple times. If running it out of the water, I'll just idle it with muffs on it.

    Oh okay, just checking. You know I had that issue once myself. It wound up being that the terminals at the battery were just loose. You need to tighten them with a socket or wrench properly and not just call it good with finger tight tension.

    I don't know if this is your problem but it is the first thing I would check.
    - 2020 Bass Tracker Classic XL - SOLD
    - 2024 Lowe Stinger 178
    Mercury 115HP ProXS CT
    Vance 6" hydraulic jack plate
    22P 3 blade Tempest Plus propeller
    NGK Ruthenium plugs
    Garmin Force troller
    Garmin 126SV/93SV/73SV Livescope/ dual GT54 transducers
    DD26 motor toter
    IG: extremeboating



  5. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #5
    Make sure you have replaced the spark plugs FRESHLY (now), with the correct plug and gap. Don't overlook this, even if they're not that old.

    Fuel Pressure should also be checked. If within spec, it may be wise to have the injectors checked again (it's been a good while).

    This particular engine DOES require a primer bulb. It already had a water separating filter inside the cowling, so be very careful about adding ANY filters, 90 degree fittings, splices, etc. Every single item added has a restrictive value that can exasperate problems.

    Also note: Idle speed, IN GEAR, should be checked on an inductive-pickup tachometer (or timing light with tach). Very limited adjustments are available on the EFI's, but I have seen a number of them that were out of "sync" (upper two throttle blades didn't match lower two). This can cause stalling.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #6
    Don, thanks. Your feedback gives me some items to pursue. Believe I'll start by replacing the plugs, bypassing the Racor and see if things improve. If not, then move forward from there. Again, input is appreciated.

  7. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #7
    Perhaps one at a time, just so you can conclusively say "that's it".


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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  8. Member
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    #8
    Update: by-passed the Racor filter, replaced the IAC/ISC valve, replaced spark plugs, checked for any loose fittings/hoses and replaced fuel lines. Still rough idle and stalling, above 1000 rpm runs great. Had Mercury mechanic coded motor and all sensors showed no issues with no alarms. He did several other tests and checks also, i.e. ignition, loose or broken wires, etc... However, problem continued so he called Mercury and talked to them. He was told the ISC should be reading around 20% at idle and it was reading 65%. They thought a possible intake manifold leak and at the higher rpm it was less of an issue with the volume of air and gas being used. We were out of town fishing so after the testing/checking I filled it up with 91 octane and put a can of Marine Seafoam in the tank. After about twenty gallons of gas going through it up at some high rpms, it started running fine. It seemed like it cleared up rather quickly as one long run and it was idling fine. I do also put Mercury Quickleen in with every gas fill. I'm no mechanic but I'm wondering if an injector was partly plugged causing the ISC to hunt trying to set the idle speed. Anyway, thought I'd pass this on as I did learn some things.
    Last edited by Shotgun1; 09-20-2021 at 02:05 PM.

  9. Member
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    #9
    Quote Originally Posted by Shotgun1 View Post
    Update: by-passed the Racor filter, replaced the IAC/ISC valve, replaced spark plugs, checked for any loose fittings/hoses and replaced fuel lines. Still rough idle and stalling, above 1000 rpm runs great. Had Mercury mechanic coded motor and all sensors showed no issues with no alarms. He did several other tests and checks also, i.e. ignition, loose or broken wires, etc... However, problem continued so he called Mercury and talked to them. He was told the ISC should be reading around 20% at idle and it was reading 65%. They thought a possible intake manifold leak and at the higher rpm it was less of an issue with the volume of air and gas being used. We were out of town fishing so after the testing/checking I filled it up with 91 octane and put a can of Marine Seafoam in the tank. After about twenty gallons of gas going through it up at some high rpms, it started running fine. It seemed like it cleared up rather quickly as one long run and it was idling fine. I do also put Mercury Quickleen in with every gas fill. I'm no mechanic but I'm wondering if an injector was partly plugged causing the ISC to hunt trying to set the idle speed. Anyway, thought I'd pass this on as I did learn some things.
    It sounds like you don't put many hours on the motor and dirty injectors are probably the problem. I see this all the time when someone sends me a set of 4 stroke injectors for cleaning and flow testing for a motor that sits for long durations. They dont have to be off that much to have a significant affect on performance. The good part is it just takes a good injector cleaning, new filters, and flow testing to bring them back. For as much as you use the motor, I would use Seafoam and Stabil every tank to keep your fuel from going bad and from gumming up the injectors from sitting for long durations. If the fuel sits in the boats tank for a few months, pump it out with a small electric fuel pump (can buy one for $20 at the auto parts store) and put it in your vehicles. Then start over with fresh gas in the boat. I live in the midwest with 2 boats that sit for 6 months over the winter and I start with fresh fuel every spring. Good Luck!!!

  10. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #10
    Quickare and Quickleen would be my choice for everyday fuel treatment. Those products are specifically designed to be safe with your engine, and contain absolutely no form of alcohol.

    The high IAC percentage (BTW... 20% is a little low) is an indication that the engine is likely running RICH and needs more air to stabilize the idle speed. Common mistake to suspect a manifold leak (which would do the same thing as opening the IAC further, causing a LEANER condition).

    At any rate- sounds like proper octane (87), fuel additives and using the engine more often may be just what the doctor ordered in this case.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor