2005 mercury 115 fuel injected 4 stroke

[sudsy]

Hi, I bought this motor second hand this year and have had a re-occuring issue with it. I have asked around to a few mechanics but havent actually brought it into anyone, so just thought i would poke peoples brains here for some ideas.


Situation: when operating the motor in gear from idle to wide open throttle, there is a dead spot in the throttle. around the 3/4 full throttle positoin the motor seems to just die for a micro second, then carry on to wide open thrrottle. If i ease the throttle back from wide open throttle to the 3/4 throttle postion the motor starts to run very rough (4500 rpm) and sounds like it is missing firing, anything on either side the motor runs fine.....


secondary issue.... about 1 out of 5 times that i run the motor up to cruising speed (4800-5200 rpm) and get to where i am fishing, i ease back on the throttle to idle (neutral) but the motor stays at 1700 RPM and wont let me get any lower and actually wont let me go to neutral (because its still too high rpm) I basically have to turn off the engine, then go to the neutral postion on the control box, then turn the motor on again..... Very frustrating....

I have done a bit of research online but havent found anything relating to my specific problems.... i have thoguth that maybe it is something with the Throttle position sensor, not sure how easy that would be to rule out or if it is related to it sticking in gear?


thanks for any help you may have to offer....

 

[sudsy]

After reading a bit online about how the fuel injection system works, im not sure if the Throttle positon sensor would cause this, i did check to make sure that my fuel injectors are all firing...i did this by puting a screwdriver up against them and listening with my ear to hear for a solenoid sound and they are all working. I have read some forums online of people having problems with the VST (vapor seperator tank) and debris collecting in there but most symptoms they describe are that they are unable to achieve anything over a certian RPM (3000rpm) my symptoms are that my motor bogs down for a split second, almost like it is dieing, then carries on to full wide open throttle....I was also suspecting a problem with the mechanical linkage in the control box itself as it is the original equipment from 1995 (quicksilver commander 3000). I have noticed a trend that anytime i get the engine bog, when i go back off on the throttle and try to put it in neutral it wont go in and is stuck at 1500 RPM (usually goes to 900 for nuetral) so not sure why the engine would be stuck at 1500....i have to turn off the engine, then it will go to neutral, then restart the motor....

81 Views and no replies...anyone have any suggestions?

 

[scott craven]

Try giving Marc Shubrook a call 250-744-9720
he runs a mobile marine repair service, I believe he is a trained Merc mechanic.

 

[GLG]

Sounds like you need to have a marine tec, with his computer, out in your boat.
You can switch sensors till you find the bad one, but that's spendy.
If you have a multimeter you can check some sensors against the specs.
But no way of knowing if the bad one will show up.
You can also ask the parts guy, at your dealer, if he has heard of this problem.
If he is good with his computer he can search what parts are regular orders.
That can be telling on sensors, if that's the problem.
There is a couple of forums that have good people in the threads.
http://www.marineengine.com/boat-forum/forumdisplay.php?30-Mercury-Mariner-Outboard-Forum
and
http://forums.iboats.com/forumdisplay.php?f=25

Remember to thank people and post the solution to your problem.

 

[trendsetter]

Does that motor have any sort of check engine light to indicate a problem or that service is required? Most newer outboards do or they have system that makes a series of beeps/tones when you first start the motor to indicate the problem. If you aren't seeing any of this I would suspect a possible mechanical problem with the throttle cable and linkages at the motor.

It's hard to figure why you might have that dead spot around 4500 RPM, that shouldn't be caused by a linkage problem. It sounds a bit like a timing issue; i.e. the ignition timing is too far advanced or not advanced enough at that RPM. Bogging is usually a fuel/air restriction but since you can go past 4500 RPM and it runs well I don't think that would be it.

Just a wild guess but it could be the powerpack or ECU that is malfunctioning or another electrical sensor in the system. The easiest way to diagnose this is to bring it to a merc shop and have them plug it into their computer and test it.

 

[Last Chance]

Post it on the Yamaha forums, it's just a rebranded Yam, and there are a lot more of them around.

 

[sudsy]

Thanks everyone for the replies, going to go to the mercury dealer tomorrow and ask them if they have any ideas or heard of anything....also check out those websites and maybe call the mobile mechanic...i do have the shop manual and the motor has a diagnostic port which you can plug a light tool into and it turns on and off to give you trouble codes, going to inquire about buying one tomorrow at mercury dealer, could be simple to make my own aswell... Il keep everyone posted, thanks again

 

[sudsy]

Just an update: went in to the mercury dealer and talked to him about my symptoms, he immedietly thought it was the throttle position sensor. Which is a high ware item on these motors, he gave me some ideas on how to check it so i went home snd hooked up the multi-meter and found that i have a dead spot in the sensor, it gradually rises from 0.68 volts and up then drops to zero volts around the 3/4 throttle position....happy i found the problem, undortunetly the part is $150 but seeing as i can install it myself and did the troubleshooting il be saving more than that in labour costs...