I have a 2002 F115 four stroke Yamaha. Nearly 900 hours of great operation until last month. Low speed idle started creeping up and within 2 days had gone from 800rpm in neutral to 1900-2100rpm in neutral. This has also affected rpm at high speed.
I have been to 2 authorized Yamaha service shops. The first (in Canada) installed a new idle control unit which worked for 2 days before problem returned. Then they tried a CPU (brain) from another boat and checked many connections and settings. No luck and I had to tow boat back home (900 miles) without fixing problem.
Next shop (in Missouri) tried putting my CPU in another F115; it made the idle increase so we figured it was the CPU. Put a good used CPU in my boat yesterday and it did not sove the problem. HELP!
9/1/11 - Thanks for all the ideas! I am not a mechanic (not even close), but there are a couple of your ideas I can check myself. To put things in perspective, I have watched the mechanic replace the ISC and I installed the used CDI. I don't know what a YDS is, but I'm guessing it may have something to do with the computers both shops hooked up to my Yamaha???
The mechanic in Canada checked many parts and settings and compared them to a new F115 he had for sale. He had some of the specs written down and gave me a copy when I left to help the solve the mystery; these included intake pressure, timing, voltage (battery and TPS, whatever that is), ISC opening %, fuel injection duration, temperatures, etc. He also said compression was good and he adjusted all of the "butterfly" settings. Below (attached) is my attempt at summarizing his hand-written notes.
He changed out the ISC and the motor ran fine for 2 days, then the low idle increased again and stayed that way; they put my old ISC back on and refunded the cost of that part before I towed the boat home (very fair on their part!). So my most recent test (yesterday) was my old ISC with the used CDICould it be that my ISC and CDI were bad??? Thanks for any more ideas.
I have been to 2 authorized Yamaha service shops. The first (in Canada) installed a new idle control unit which worked for 2 days before problem returned. Then they tried a CPU (brain) from another boat and checked many connections and settings. No luck and I had to tow boat back home (900 miles) without fixing problem.
Next shop (in Missouri) tried putting my CPU in another F115; it made the idle increase so we figured it was the CPU. Put a good used CPU in my boat yesterday and it did not sove the problem. HELP!
9/1/11 - Thanks for all the ideas! I am not a mechanic (not even close), but there are a couple of your ideas I can check myself. To put things in perspective, I have watched the mechanic replace the ISC and I installed the used CDI. I don't know what a YDS is, but I'm guessing it may have something to do with the computers both shops hooked up to my Yamaha???
The mechanic in Canada checked many parts and settings and compared them to a new F115 he had for sale. He had some of the specs written down and gave me a copy when I left to help the solve the mystery; these included intake pressure, timing, voltage (battery and TPS, whatever that is), ISC opening %, fuel injection duration, temperatures, etc. He also said compression was good and he adjusted all of the "butterfly" settings. Below (attached) is my attempt at summarizing his hand-written notes.
He changed out the ISC and the motor ran fine for 2 days, then the low idle increased again and stayed that way; they put my old ISC back on and refunded the cost of that part before I towed the boat home (very fair on their part!). So my most recent test (yesterday) was my old ISC with the used CDICould it be that my ISC and CDI were bad??? Thanks for any more ideas.
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