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Mercury 115 hard start problem

T

Tonyk1984

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I have an 09 mercury 115 EFI four stroke s/n 1B738410. Motor starts fine when unloading at ramp. Idles fine. Throttle up and it gets to 3,500 rpms then starts to act bogged down. Finally will plane out and reach WOT. Idle back down and sometimes it acts like it might die when getting near neutral. Leave it running and take it back up to WOT with no hesitation. Let it sit for a bit while fishing and it is hard to start but eventually does. Same thing happens with difficulty getting on plane. Changed float in FSM, had injectors cleaned and tested, changed all fuel filters and spark plugs, new fuel pressure regulator. Nothing helped. Had computer innit and not throwing any codes, mechanic couldn’t replicate problem in the tank. Any thoughts? Mechanic thinks maybe weak fuel pump? I did notice that there was an unusual amount of sand in water pump when I changed it, maybe a bad thermostat now? Everything on this motor costs at least $100 so I’m tired of guessing.
 
30 views and no replies?!?! I need some help guys! Are these four strokes nothing but problems or what?!? Never had any trouble out of my old two stroke
 
OK.....

What color is the potting in your ignition coils?

Do you have an anti-siphon valve on your fuel tank?
Do you have a inline fuel water sep filter?
Do you have a primer ball on the fuel line?
 
I would have thought the computer would have said if TPS was out of spec. I don’t know what color ignition coil is but will check and get back to you. Yes I believe there is an anti siphon valve in the tank. I have run an auxiliary portable tank with same issues. No primer bulb on my set up. No water fuel separator but I have siphoned all the gas out and re fueled with ethanol free. No change. I have noticed a little white smoke at times when having this problem also seen a small “oil slick” coming from prop sometimes when this happens. I checked lower unit and no leaks so I’m assuming it’s fuel and oil. What exactly do you mean by “potting” in ignition?
 
That the triple nickle ECM and it should have tripped a code..it wont if stripped internally. Also check MAP sensor. I have heard that the TPS is the same as used on mid 90's Chevy
 
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Tonyk1984 said:
I looked at my coils but obviously I’m not sure what I’m looking at. They just look black.
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If they are black then they are probably good.
You will not have any codes stored in the Module when you have a fuel delivery issue.
I am suspecting that your low pressure (lift)fuel pump is working intermittently. You will have to isolate the wires on the FSM plug for the lift pump and check the amperage draw when the issue occurs.
 
Would the lift pump going out cause the oil slick? It almost seems like it’s getting too much fuel to me. If the lift pump couldn’t keep up wouldn’t it act like it was out of gas or actually die at top speed? I will check that though for sure it may be a few days before I can because I actually have to get it on the water for that and where I live lakes are all about 60 miles away so it’s a pain to go to just test
 
Tonyk1984 said:
Would the lift pump going out cause the oil slick? It almost seems like it’s getting too much fuel to me. If the lift pump couldn’t keep up wouldn’t it act like it was out of gas or actually die at top speed? I will check that though for sure it may be a few days before I can because I actually have to get it on the water for that and where I live lakes are all about 60 miles away so it’s a pain to go to just test
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You are probably seeing fuel in the water.
If the fuel pressure drops at the injectors (FSM Empty/extremely low) the fuel will not be atomized(fuel just drips out of the injector) and just pass through the engine and into the water.

You will want to check this, low fuel level in the FSM will damage the high pressure pump.
 
Thank you I will check those. The mechanic I took it to said he thought duel pumps also. Is this a common problem with these? The fuel pumps are expensive from what I’ve seen $300 each. Any chance I could find some cheaper?
 
Chris, do you think that there is anything to my t-stat theory? Would mechanic have found that with computer if thermostat was working intermittently? I’m just worried about it because of the sand and damage I saw in the water pump housing. Dang t-stat is $100!! Crazy
 
Chris, I checked the lift pump and it was weak. Replaced it and now it jumps on plane like it should! Thanks. I still occasionally have the hard start issue after it’s run full throttle. What I have noticed though is that if I slow down to idle after WOT and let it idle for about 30 seconds or so then shut it off it starts right up. Still stumbles a little if backing off the throttle too fast.
 
Tonyk1984 said:
Chris, I checked the lift pump and it was weak. Replaced it and now it jumps on plane like it should! Thanks. I still occasionally have the hard start issue after it’s run full throttle. What I have noticed though is that if I slow down to idle after WOT and let it idle for about 30 seconds or so then shut it off it starts right up. Still stumbles a little if backing off the throttle too fast.
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Good to hear.
For the hard restart, Make sure you have good water flow through the FSM...


As far as the stumbling, I would wait until it becomes a real problem. You will be able to pinpoint it. Something on the control side of the engine may be "failing in range" that will be hard to find until it totally fails.
 
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