Yamaha F75 idle issues....

[kathys1guy]

Hi All;
I have been researching this one for a while. A few months ago, after running a load of family up the lake at cruise speed, when I went to reduce the power to idle, it stayed around 2000 RPM. After restarting, the idle returned to normal. It started up with no problem and it did not occur for a period of time after that. Since then I did routine maintenance which included oil/filter change, lower end lube change, and new NGK LFR5AIX-11 Iridium plugs gapped to .040 (.040-.044 normal). They were the original plugs, standard NGKs LFR5A-11 and were very clean with about 330 hours on them. On the test run after maintenance, it started right up, idled smooth when cold, accelerated nicely ran at high cruise (5000 rpm), reduced power to idle, now it delayed at 2000+ RPM then drifted to about 1500 and fell off to 1000 RPM, now running rough like 1 cylinder was not firing. Back 2 the shop (my home), filled the half tank of fuel to full with mid-grade and to cans of Sea Foam engine and fuel system cleaner and installed a fuel/water seperator. Rechecked plugs and test ran again...same results. Upon securing boat at home , noticed primer bulb was leaking...replaced, same results. Now thinking plug issues...reinstalled original set of plugs cleaned and gapped to .040, test ran...same reults. With the Computerized igniton and fuel injection, I am just about ready to give up and send it into the Yamaha dealer. By the way, at their direction, I did empty out the canister from the fuel/water seperator and it appeared clean...HELP...Please! Thanks in advance

 

[kathys1guy]

Re: Yamaha F75 idle issues....

Hi All;
I have been researching this one for a while. A few months ago, after running a load of family up the lake at cruise speed, when I went to reduce the power to idle, it stayed around 2000 RPM. After restarting, the idle returned to normal. It started up with no problem and it did not occur for a period of time after that. Since then I did routine maintenance which included oil/filter change, lower end lube change, and new NGK LFR5AIX-11 Iridium plugs gapped to .040 (.040-.044 normal). They were the original plugs, standard NGKs LFR5A-11 and were very clean with about 330 hours on them. On the test run after maintenance, it started right up, idled smooth when cold, accelerated nicely ran at high cruise (5000 rpm), reduced power to idle, now it delayed at 2000+ RPM then drifted to about 1500 and fell off to 1000 RPM, now running rough like 1 cylinder was not firing. Back 2 the shop (my home), filled the half tank of fuel to full with mid-grade and to cans of Sea Foam engine and fuel system cleaner and installed a fuel/water seperator. Rechecked plugs and test ran again...same results. Upon securing boat at home , noticed primer bulb was leaking...replaced, same results. Now thinking plug issues...reinstalled original set of plugs cleaned and gapped to .040, test ran...same reults. With the Computerized igniton and fuel injection, I am just about ready to give up and send it into the Yamaha dealer. By the way, at their direction, I did empty out the canister from the fuel/water seperator and it appeared clean...HELP...Please! Thanks in advance

August 8, 2009
Hello again all...a quick update and still have the problem. The Yamaha dealer pulled up some codes on the computer and found an air flow problem which led to the replacement of the Idle Speed Control Valve that had a metering rod sticking. They said they were getting electrical power to the valve, but it was not moving as it was designed and replaced it at $211.00 for the part and about $135 labor. They did a tank run of at only 4000 RPM since their tank would empty out at WOT. Everything checked out.....until today! Took it out for a shakedown on the lake and after 20 minutes ,10min of WOT, backed off the throttle slowly to idle. Decreasing RPM through 2000 RPM, idle stayed there. It slowly drifted down to about 1200 RPM then started to act like it was missing on one cylinder and tried to hold idle at about 800 RPM with a very consistant miss-like rough idle. Now I am thinking ignition (plug lead or powerpack?) after it gets heated up, gets some sort of breakdown. Possible computer? PLEASE ANYBODY...HELP?? My season is diisappearing rapidly as our lake is going down 2 feet/day and ramps will be out of the water in about 10-15 days!!

 

[rodbolt]

Re: Yamaha F75 idle issues....

I would lean towards a bad ECU or a faulty ECU ground.
at idle most all the air the engine is burning comes through the ISC valve. it will open and close slightly to aide in idle stabilizarion.
at wot its open 100% and about 60% at idle.
if it sticks at 100% you will ger a high idle.
if it sticks it can and will overheat the ECU and funny things happen.

 

[kathys1guy]

Re: Yamaha F75 idle issues....

Rodbolt...thanks so much for the reply. Your timing is impeccable. I was just calling the Yamaha Dealer in my area (about 45 miles away) to arrange to bring it back. The problem they have is that their run tank will only allow my motor to get up to about 4000 RPM. Any higher and their tank evacuates copious amounts of water and thus not able to get the motor back upto WOT where the start of the problems occur. I will take a copy of these posts to the mechanic to give them as much info as possible. I'll let you know how it turns out....THANKS AGAIN

 

[kathys1guy]

Re: Yamaha F75 idle issues....

Hi Rodbolt...brought boat back today,briefed mechanic with these narratives printed in hand. Told him about your response. He said he has never seen the Yamaha computers overheat. He will go through another dianostic check with the software and see what we get. He is still workin' on it...thanks again..

 

[kathys1guy]

Re: Yamaha F75 idle issues....

I would lean towards a bad ECU or a faulty ECU ground.
at idle most all the air the engine is burning comes through the ISC valve. it will open and close slightly to aide in idle stabilizarion.
at wot its open 100% and about 60% at idle.
if it sticks at 100% you will ger a high idle.
if it sticks it can and will overheat the ECU and funny things happen.

Hi Rodbolt. Extremely sorry for the late thanks on your input to this thread. Had a lot of personal health issues that got in the wqay. After nissing almost the entire season with the repair of this issue, thought I would followup with the update. Many hours of constant running at the shop, the intermittant condition returned in the mechanic's presence...a bad harness feeding the ISC valve. He wiggled the harness and was able to duplicate the problem. About a $1200 repair in all (new harness). The new computer actually made the boat run worse and they went back to the original computer. After I got the boat back, runs great by the way, my new problem is that I think the mechanic did not connect uo the trim/tilt indicator harness. The indicator indicates full up, The cam is still intact and in place. What wires would I look for to make sure the connection is done properly. I would hate to make another 90 mile roundtrip to the shop! Thanks in advance...

 

[rodbolt]

Re: Yamaha F75 idle issues....

tech should have caught a wiring defect with the laptop.
unplug a wire and you get a code.
you can also use the laptop to cylce the ISC both dynamicly(engine running) and statically,engine off valve in your hand and watch the pintle movement.
look at that little arm at the trim cam, does it follow the cam or lift off when trimming up?

 

[kathys1guy]

Re: Yamaha F75 idle issues....

Thanks Rodbolt...traced the harness from the trim indicator transducer back into the engine cowl and found the other end of the plug, underneath other wires, totally disconnected. Matched it up with it's cooresponding mate and it now works great. Thanks again for all your help!

 

[ebraker]

Re: Yamaha F75 idle issues....

Hi Rodbolt: seems I'm having a return to idle issue you might be able to help with: My 2000 F50 (carburated) does not always return to idle after a few minutes at WOT. It starts and idles easily, has a new water pump impeller, throttle return dashpot is set correctly, fuel lines have been blown out, engine and boat fuel filters have been changed. It seems to hang up anywhere between 1600-3300, and when switched off, it sometimes restarts with a normal idle. Gently pulling down on the large vacuum device that's linked to the top cylinder throttle plate rod (and thereby the other 3 cylinders) immediately returns the engine to idle. It appears as if the device is not working, or it's linkage is sticking, or maybe it has nothing to do with it. It does have a vacuum line running to each carburetor. I have also disconnected the throttle cable, but the hang up still occurs. Appreciate any ideas.