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Author Topic:   2004 Mercury 115 FOURSTROKE: Misfire

Marsh posted 09-11-2013 03:34 PM ET (US)
I have a pesky engine miss that I can't get rid of. Things I have already done include:
--adding Sea Foam to fuel,
--changing fuel tank and fuel,
--changing spark plugs,
--replacing fuel filter.
Still the misfire persists. Before I haul it out and take it to a service tech, is there anything else I should try? Engine has only 120 hours on it. When changing fuel filter, I noted a small amount of sediment in the bottom of the filter canister, which I thoroughly cleaned before replacing the filter cartridge with a new one.
Thanks for any advice.
L H G posted 09-11-2013 05:22 PM ET (US)
I would take that Yamaha EFI engine to a Yamaha dealer for service. My experience with EFI is that they are not easy for the owner to diagnose problems and to work on.
Marsh posted 09-18-2013 04:14 PM ET (US)
I called a "Mercury" repair shop - the one closest to me. Asked the service guy if they worked on the Mercury 4-stroke engines made by Yamaha. He said he had never heard of Mercury engines made by Yamaha. I told him thanks, that he had answered my question. I took my repair work back to my selling dealer, even though he is 50 miles further away. Crossing fingers here.
L H G posted 09-18-2013 06:06 PM ET (US)
Your service guy should talk to JimH. Jim will set him straight.
jimh posted 09-18-2013 07:13 PM ET (US)
Naw, the service guy should just read the testimony of the United States International Trade Commission. That is where the real truth comes out. You can find the transcripts on-line, and they make interesting reading. They put to rest a lot of internet blustering.
jimh posted 09-19-2013 10:51 AM ET (US)
It is understandable that a typical Mercury dealer might not be able to provide good service for that engine. Mercury was buying so many engines from so many different other manufacturers that their service people must have been pulling their hair out trying to keep up. That engine is from an epoch when Mercury had no four-stroke-cycle engines of their own, and they just bought engines from Yamaha and painted them black. The poor technician at a Mercury dealer probably never got any good training on servicing those engines. This may explain why we see so many problems reported with the Mercury-branded versions of these engines compared to the Yamaha branded ones. The Yamaha branded engines were probably set-up and serviced by technicians who got some training. The poor Mercury dealer was in a whirlwind of different engines being sold under the Mercury brand. Look at the crazy position a Mercury dealer would be in back then. He'd have to be trained and qualified to service all the Mercury engines and then be trained and qualified to service all the Yamaha engines, too, as that is what Mercury was selling at that time. At that time, Mercury was one of the biggest importers of four-stroke-cycle engines made in Japan. This all came out in the USITC investigation.
jimh posted 09-19-2013 10:58 AM ET (US)
But all this sidebar discussion started by LHG is not helping your misfire.
A misfire sounds like an electrical problem. I don't think the method of fuel induction--electronic controlled throttle body injection or carburetor--is going to affect the electrical spark generation.
Test the spark using an in-line spark gap test tool. See if you can find a cylinder with weak spark or no spark. Check the plugs for proper gap and for good condition. Check the spark plug wires--some of those Yamaha high-voltage spark leads have a tendency to work loose from the plug. (On my Yamaha outboard I resorted to using nylon ty-wraps to secure the rubber boot to the plugs.) If you find one cylinder is showing something odd, try switching the spark coil from that cylinder with one from another cylinder.
Also check the neutral cut-out switch (if that engine has one). This is usually on the shift linkage and cuts out a few cylinders during shifting. If the alignment of the switch and shift linkage is not just right, it might be cutting out a cylinder at an inappropriate time.
Marsh posted 09-20-2013 04:33 AM ET (US)
Turns out all my trouble was due to mis-routed plug wires. Apparently, sometime early this summer, my plug wires got crossed. That's when the engine began to mis-fire. Then when trying to solve the mis-fire, I replaced the plugs, and unwittingly left the plug wires oriented the same way, hence the miss continued. Changing the fuel, fuel tank, and the fuel filter would obviously have had no impact.
I dropped off my boat, motor, and trailer at the Mercury dealer on Wednesday afternoon. On Thursday morning, I got a call saying it was ready, and running like new, with properly routed plugs wires.
Since my boat lives on a hoist, on a lake with a constant parade of boaters, fishermen, and PWC riders of all types, and since I have two neighbors who love practical jokes, I am wondering if someone popped my engine cover, swapped plug wires, and replaced the cover. Could be easily done in two minutes or less. I can't see any other way plug wires could spontaneously be mis-routed. The engine only has a little over 100 hours on it. I don't mess with plug wires when changing oil. Hmm.
jimh posted 09-20-2013 09:19 AM ET (US)
Thanks for the follow up. Your story reminds me of a similar incident from years ago. I worked with a bunch of engineers who liked practical jokes. I had just bought a new car, and I was bragging about how well it ran and the great gas mileage I was getting. One of the guys snuck out and swapped the spark plug wires on my engine. When lunch time came, we were going to go in my car so everyone could see how well the engine ran. To the amazement of the guy who swapped the plug wires, the engine started and seemed to run normally. At that point he confessed to what he had done, and we restored the plug wires to their normal positions.

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Author	Topic: 2004 Mercury 115 FOURSTROKE: Misfire
Marsh	posted 09-11-2013 03:34 PM ET (US) I have a pesky engine miss that I can't get rid of. Things I have already done include: --adding Sea Foam to fuel, --changing fuel tank and fuel, --changing spark plugs, --replacing fuel filter. Still the misfire persists. Before I haul it out and take it to a service tech, is there anything else I should try? Engine has only 120 hours on it. When changing fuel filter, I noted a small amount of sediment in the bottom of the filter canister, which I thoroughly cleaned before replacing the filter cartridge with a new one. Thanks for any advice.
L H G	posted 09-11-2013 05:22 PM ET (US) I would take that Yamaha EFI engine to a Yamaha dealer for service. My experience with EFI is that they are not easy for the owner to diagnose problems and to work on.
Marsh	posted 09-18-2013 04:14 PM ET (US) I called a "Mercury" repair shop - the one closest to me. Asked the service guy if they worked on the Mercury 4-stroke engines made by Yamaha. He said he had never heard of Mercury engines made by Yamaha. I told him thanks, that he had answered my question. I took my repair work back to my selling dealer, even though he is 50 miles further away. Crossing fingers here.
L H G	posted 09-18-2013 06:06 PM ET (US) Your service guy should talk to JimH. Jim will set him straight.
jimh	posted 09-18-2013 07:13 PM ET (US) Naw, the service guy should just read the testimony of the United States International Trade Commission. That is where the real truth comes out. You can find the transcripts on-line, and they make interesting reading. They put to rest a lot of internet blustering.
jimh	posted 09-19-2013 10:51 AM ET (US) It is understandable that a typical Mercury dealer might not be able to provide good service for that engine. Mercury was buying so many engines from so many different other manufacturers that their service people must have been pulling their hair out trying to keep up. That engine is from an epoch when Mercury had no four-stroke-cycle engines of their own, and they just bought engines from Yamaha and painted them black. The poor technician at a Mercury dealer probably never got any good training on servicing those engines. This may explain why we see so many problems reported with the Mercury-branded versions of these engines compared to the Yamaha branded ones. The Yamaha branded engines were probably set-up and serviced by technicians who got some training. The poor Mercury dealer was in a whirlwind of different engines being sold under the Mercury brand. Look at the crazy position a Mercury dealer would be in back then. He'd have to be trained and qualified to service all the Mercury engines and then be trained and qualified to service all the Yamaha engines, too, as that is what Mercury was selling at that time. At that time, Mercury was one of the biggest importers of four-stroke-cycle engines made in Japan. This all came out in the USITC investigation.
jimh	posted 09-19-2013 10:58 AM ET (US) But all this sidebar discussion started by LHG is not helping your misfire. A misfire sounds like an electrical problem. I don't think the method of fuel induction--electronic controlled throttle body injection or carburetor--is going to affect the electrical spark generation. Test the spark using an in-line spark gap test tool. See if you can find a cylinder with weak spark or no spark. Check the plugs for proper gap and for good condition. Check the spark plug wires--some of those Yamaha high-voltage spark leads have a tendency to work loose from the plug. (On my Yamaha outboard I resorted to using nylon ty-wraps to secure the rubber boot to the plugs.) If you find one cylinder is showing something odd, try switching the spark coil from that cylinder with one from another cylinder. Also check the neutral cut-out switch (if that engine has one). This is usually on the shift linkage and cuts out a few cylinders during shifting. If the alignment of the switch and shift linkage is not just right, it might be cutting out a cylinder at an inappropriate time.
Marsh	posted 09-20-2013 04:33 AM ET (US) Turns out all my trouble was due to mis-routed plug wires. Apparently, sometime early this summer, my plug wires got crossed. That's when the engine began to mis-fire. Then when trying to solve the mis-fire, I replaced the plugs, and unwittingly left the plug wires oriented the same way, hence the miss continued. Changing the fuel, fuel tank, and the fuel filter would obviously have had no impact. I dropped off my boat, motor, and trailer at the Mercury dealer on Wednesday afternoon. On Thursday morning, I got a call saying it was ready, and running like new, with properly routed plugs wires. Since my boat lives on a hoist, on a lake with a constant parade of boaters, fishermen, and PWC riders of all types, and since I have two neighbors who love practical jokes, I am wondering if someone popped my engine cover, swapped plug wires, and replaced the cover. Could be easily done in two minutes or less. I can't see any other way plug wires could spontaneously be mis-routed. The engine only has a little over 100 hours on it. I don't mess with plug wires when changing oil. Hmm.
jimh	posted 09-20-2013 09:19 AM ET (US) Thanks for the follow up. Your story reminds me of a similar incident from years ago. I worked with a bunch of engineers who liked practical jokes. I had just bought a new car, and I was bragging about how well it ran and the great gas mileage I was getting. One of the guys snuck out and swapped the spark plug wires on my engine. When lunch time came, we were going to go in my car so everyone could see how well the engine ran. To the amazement of the guy who swapped the plug wires, the engine started and seemed to run normally. At that point he confessed to what he had done, and we restored the plug wires to their normal positions.