2002 Merc 115 Fourstroke EFI

[Marble Eyes]

I have a Mercury 115 fourstroke EFI which I bought new in May 2002. It has been running perfectly until now. Cruising at about 5000 RPM it began cutting out. It would cut out and then come right back up to power. All within about one second. The tach drops right down to about 1000 RPM and come right back up again. Originally it did not seem to change with RPM but now if cruising at 4000 RPM it goes for quite awhile without a hiccup but when I bring it up to about 4600 RPM or more it cuts out and comes back up varying in frequency from every few seconds to every few minutes. The dealer originally thought it might be water in the fuel but it happens so quickly and varying with RPM I think it is electrical. I have not brought it to the dealer yet. Any Ideas? This is my first ever posting on a forum. Any help would be appreciated before I take it to the dealer. Warranty has technically expired in May(Great timing eh?)

 

[JB]

Re: 2002 Merc 115 Fourstroke EFI

Howdy, Marble Eyes.<br /><br />Welcome to iboats. <br /><br />If you don't have a water seperating fuel filter I am inclined to agree with your dealer. In any event, if you don't have one you need one.<br /><br />Try it with a portable tank and fresh fuel.<br /><br />Good luck.

 

[Dunaruna]

Re: 2002 Merc 115 Fourstroke EFI

The dealer should be able to diagnose an electrical fault by reading the codes, at the very least it will give him a starting point.<br /><br />An EFI definetely should have a water seperator, unlike carby's, they don't handle water at all.<br /><br />IMO they should be fitted as standard equipment, not an 'optional extra'.<br /><br />Aldo

 

[Marble Eyes]

Re: 2002 Merc 115 Fourstroke EFI

It is now in the middle of winter and it is time I post a reply and let everyone know what the actual problem was with my Merc 115 EFI momentarily cutting out. I took my boat to the Merc dealer in Kenora, Ontario and had them check it out. They spent a whole day swapping out the ECU and the high pressure fuel pump and checked the fuel pressure. None of these solved the problem. Then they swapped out the tachometer with a test tachometer. This fixed the fault. They ordered a new Merc tach and installed it. I picked up the boat, put it back in the water only to find out the fault was still there. I was not happy! I brought the boat back again. A few days later I called them and they again said it was a defective tach. They replaced it again. The engine runs fine now. Can you believe it? <br />I asked why the diagnostice codes from the engine could not have picked out a bad tach. They told me that beacuse it is a Yamaha engine, Merc is given very few diagnostic codes for finding faults. I would think that a defective tach that can actually cause a failure in the engine should be something that the diagnostics should be able to find and generate an error and not have to spend hours swapping modules only to find out that the fault was actually not in the engine but an external device. By the way, disconnecting the tach did not make the fault go away. It seems that the engine must get some feedback from the tach. This to me seems like a serious design flaw. I will be sending a message to Mercury and see what they have to say about it. Anybody know who at Mercury I should send it to? I would like to hear any comments you might have about this whole problem Thanks.

 

[rodbolt]

Re: 2002 Merc 115 Fourstroke EFI

seems your techs are clueless. the tach has no feedback circuits and the ECU could care less if the tach is installed or not.<br /> my money will be on a partially clogged injector or a vapor seperator filter or a loose connection. if all they did was change the tach odds are its still broke. the F115 ECU does not give much information yet the merc F115 manual is far superior to the yamaha manual. trust me on this. I would suggest popping out the injectors and cleaning the injector filters and cleaning the VST filter then install the yamaha 10 micron water seperating filter. but that motor is very easy to test. there is just not much that goes wrong, the ign system is battery powered as are the injectors and the fuel pump. bad cable connections or a faulty main relay will create a momentary shutdown. its amazing though how quick the engine will miss if it cannot maintain 35PSI on the fuel rail. its not usually a gradual power loss.<br />not at all like a carb. the ECU generates the tach pulses on that motor and like I say it does not care if a tach is installed or not.<br /> about the only codes the F115 sets is,pulser signal13,thermosensor 15,tps 18,battery voltage19,atmospheric pressure sensor 22,intake air temp sensor23,shift switch position 28,intake air pressure 29,idle speed control 37,buzzer signal recognition 43, stop switch recognition 44and overcooling 49. not all F115 motors have all the signals. the early 02 and older only set about 8 of them. you can also check for codes with a 12 lamp and some pigtails a laptop is not nessasary. my suggestion is to ask to see the school training manuals not service manuals your techs are using.<br /> the most commonly used codes on your engine will be,13,15,18,19,23,29,33(engine cold)37 and 44. but dont let the techs baffle ya with BS, ask to see their training certs. the merc techs have better manuals than us poor yammie techs. I have both manuals .

 

[Marble Eyes]

Re: 2002 Merc 115 Fourstroke EFI

It has a few years since I had this problem with my Merc. After changing the tach a second time, it was fine for awhile and then it started cutting out again. I put a scope on the tach output from the engine (the signal going to the tach which comes from the ECU)and when the fault happened there was no signal coming from the engine.This time I took it back to the dealer. The tech spent considerable time on it (swapping every related part)but none of these cured the problem. In the end he replaced the entire engine wiring harness. The engine has worked fine since. It was not the tach or a fuel problem. I thought I should reply with the actual fix even though it has been awhile. Thanks for all your help.