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2002 Mercury 115 Fourstroke idle issue HELP!

M

Masher

New member
Hi,
I have a 115 fourstroke mercury 2002 model with the Yamaha power head (534 hours on the ECM). The motor will not idle after a run of about 30 minutes or more. It will cough and splutter for some ten minutes while I keep it going with the warm up leaver and then as if by miracle just comes good running perfectly. If I put the throttle down to get the revs up about about the 1500revs it runs fine developing 5600 revs AWOT. I have used a YDS and checked and done many things to no avail. 1. Checked the cooling system and replaced grommet seal under the powerhead. This seal had broken apart and gone through the motor. We found some of it caught at the water outlet side of the powerhead. Changed thermostat, temperature sensor, water pump impellor. On the fuel side I have had new injectors, new low pressure fuel pump diaphragm, cleaned the filter inside the high pressure pump chamber. Checked the flow on the fuel water cooler. I have replaced the entire IAC valve and associated assembly. The YDS is giving some eractic readings at idle with the comparison between the IAC open percentage being inconsistent with the Thotte opening degrees to the revs. The problem I have is that the motor does not show the simptoms when cold so the mercury mechanic can never see the issue - the motor runs fine and unfortunately I don't know a mechanic well enough to come for a longer run to see the issue? Any thoughts would be greatly appreciated. Lastly the diagnostic is saying the Throttle position sensor had had an error at about 100 hours ago and the diagnostic shows at stop/off ignition negative .5 degrees and outlines the information in red. Any thoughts apart from sinking it would be greatly appreciated.
regards
Masher
 
''diagnostic shows at stop/off ignition negative .5 degrees and outlines the information in red.'' does the diagnostic fail now or is that too from 100 hours ago?to me this is a fix what you can see and this is your only clue....a good merc man with the mercury support available to him from mercury should be able to solve this...if this is an old one time failure then the failure would drop in priority of course but mercury support should still be able to give him a quick answer on it...some shops have a test tank and i would deal with a merc shop that has one..back the boat up to the tank and let it run under load til it fails...this will be cheaper on labor cost than him putting it in the water and trying to duplicate the problem.....plus he has all his diagnostic tools handy including the telephone to merc support for his computer hookup...this mercury support cost the guy money...he has to pay for updates on his diagnostic discs etc...but i would not deal with a shop that does not do this...they are shotgunning without this support on computer driven motors......if you dont urgently need the boat most of the time the guy will charge you less if you can leave it and he can work on it without time restraints...time is money to him and a good relationship is worth the time it takes to develop it..
 
Hi I"m interested in being in contact with other 2002 Merc 115 efi four stroke owners. always good to know others with similar motors.

While reading the this thread Papyson is complety correct with his comment of using a mechanic with tub and support diagnostics.

While on that note I did not know this motor had enough computer hard drives to do diagnostics, great news.

is 5600 rpm the reccommended max? I ask as I've not found this info anywhere else, With my prop set up I can get 6000rpm but bring it down as I just generally figured 6000 may be to high.
your ideas?
cheers
 
I am not sure if you specified weather your 115 is fuel injected or carbureted. The carbs on the 115s are notoriously sensitive and any slight amount of debris in them will cause your engine to run weird. They also have to be synchronized with a vacuum gauge if any work is done to them. I've rebuilt hundreds of them.

Check your fuel as a first precaution. Ensure that you are delivering clean, crisp, and water free fuel to your engine. If you do, and you have an EFI, we'll take it from there.
 
Masher, did you ever find out what the problem is? My 115 is doing the same thing and it driving me nuts. I also did and changed all the parts as you noted in your post.
 
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