F115 IAC Valve

[JONSNELL]

Will my 2002 F115 run with the plug to the IAC disconnected ?

Reasoning - My IAC is not working but is stuck at a level which provides an acceptable idle ie 880RPM. I know this my not be so good if it is cold but I can disengage the gears and life my cold start RPM that way. I'm in the tropics so cold is not a big issue.

Would prefer not to risk burning out that part the the ECU.

Thanks JON

[rodbolt17]

then keep the ISC valve unplugged.
myself?
I would wait,get the part, fix it correctly then run it.

[JONSNELL]

The reason I asked is I have a charter tomorrow and was concerned that the new part would not arrive in time.

Anyway - good news - new IAC arrived today

Bad news - installed new IAC and run static test and cant hear the IAC.

Will run active test later today but cant say I'm confident of it working.

So this problem that has been occupying my mind/ruining my life for a few weeks now remains ongoing.

Will use the boat tomorrow on the basis that I cant do any further damage to the ECU now that I have a new IAC installed.

Since my diagnostic when running the active test on the IAC changes % value it would appear to me that the ECU is still OK - is this correct ?

Then based on that then it can only leave the wiring to be the problem.

Thanks again for peoples input.

Snelly

[JONSNELL]

Yep as I suspected no change with the active test. On the screen it shows the IAC % going from 100 down to 30 but no change in RPM.

[JONSNELL]

Run the boat yesterday - fired up and idled fine. Went to first spot and went to move all OK , second spot and she will not fire up. Manage to get her to start by disengaging gears but would not allow me to bring back to neutral. I ended up disconnecting the start in gear switch and starting in gear. Managed to get through the day that way and she did start a couple of times in neutral but idle was 4-500RPM.

My thoughts are that the IAC may be operating intermittently and has now adjusted to further closed.

[rodbolt17]

my thoughts?
fix the dang thing BEFORE you kill your charters.
dang mercial fishermens.

I understand, gotta go gotta go.
I work with it daily.
however some times its best to find a dealer that understands and doesn't mind your gotta go.

[JONSNELL]

I'm trying to do my best with what I have to work with - all I want is to see it fixed and an end to my situation.

I'm not sure how to say this without getting anyone offside but I cant under stand why I have not got a reply to my question re my ECU based on the information I have given. If I'm missing something then let me know.

I have booked my outboard in to be looked at next week but I feel that I may not get a proper resolution ( ie dealer will tell me it all checks out and there are no fault codes ) as has happened to people in the past with the same problem.

I would never put myself or anyone else for the matter at risk.

[99yam40]

have you made sure the ECU has an output that gets to the plug at IAC or where it leaves the ECU?
If it has an output but not getting to IAC then it is a wiring problem.
Sorry but I have no idea even if you can get to the ECU out put connections, but seems like that should be possible

[JONSNELL]

Took it to the local Yamaha dealer today and was told the brand new IAC I got last week is not working ( and want to order a new one ) as it is not letting the motor idle at the correct RPM ..... well that is what I told them in the first place. They said they tried another IAC and it work fine and idled at 800rpm - what they didn't say is if they run the diagnostic test .. somehow I don't think they did. Anyway I gave them the secondhand one I had as I know it will allow the motor to idle at 800rpm and will see what they say about that. I'm concerned that they will say its fixed just because it now idles at the correct RPM. This is what happened when I put the new one in last week idles at 800 RPM but then for what ever reason through the day the idle reduced to a level where it wouldn't run. What also concerned me is I asked if they could bench test the IAC and they said not. Yet as you guys have said it can be easily done. I did try to test my origional one and got it to try and start to move but nothing more. I never tried the new one as I was fearful of damaging it.

Anyway will see what tomorrow brings but at the moment I cant say I'm confident.

[rodbolt17]

the ISC valve is a simple stepper motor.
was used in both a 4 and 6 wire configuration over the years.
the 4 wire is a single speed the 6 wire is a dual speed.
at key on 12V is applied through both the fwd and rev direction windings.\

with no ground path the 12V simply sits there like a bump on a log.

to adjust the idle speed the ecu requests a % change in the ISC valve opening.

so the ecu toggles the ground and ASSUMES the valve followed the command.

which is why when you shut the key off,after the engine actually ran, you hear the ISC rattling.

at engine shutdown the ECU sends a request for something between 67 and 100% opening(model dependant) in anticipation for the NEXT start cycle.

the ECU does not and cannot monitor the ISC for a physical position nor for the fact it can even move or the circuits(wiring harness,powersupply) is good.

the ECU to ISC is a rather stupid relationship.

the ECU looks at the TPS input,crank position input and map inputs and determines ISC position for the best idle speed.

the ISC is NOT designed to have a constant on time, it has a rather limited duty cycle.

IF the idle speed does not do what its supposed to the ECU will keep sending requests and the duty cycle increases to the point where something,typically the ECU,overheats and bites the dust.

at the end of the day? the ISC valve is a DC motor similar to a trim motor.
polarity change(which windings selected) determines what way the motor runs and either extends or retracts the valve.

its not complicated,it does require an understanding of how it works.
once the ISC moves,or not, the ecu removes the ground path and the circuit is dead and the ISC stays there until its toggled again.

if it does not move the ECU does NOT know that mechanically it failed to move.
the only thing the ECU "sees" is the idle speed failed to follow the request so the request keeps being sent and the ground path toggled.

typical ISC requests will fall between about 47% to about 65% while idling,much below and you may have excess air entering the intake manifold,much above and the passages are clogged or shutters are out of sync.

[JONSNELL]

The dealer today located some ground wires that were loose. He completed a reset and resync and the engine idled fine. He said that he had the ISC valve operating with the diagnostic. I was asked to take the boat for a run, before I run it I hooked up the computer and no response from the ISC static test. Put the boat in the water and run it - idled fine but no response form the active test. Then when I run it the idle gradually picked up to 1500rpm.

Mechanic thinks that the loose grounds may have damaged the ECM.

So they are to do another test on the wiring but I'm thinking the ECM will need replacing so it appears that even though the ECM can give out a signal to the diagnostic program it doesn't mean it is operating the ISC.

My question at the moment is what has peoples experiences been with this models ECM ? OK I know that a stuck ISC can/does burn that part of the ECM out other than this do they fail often ? I'm asking this as I'm considering my options of a secondhand part v's new.

[99yam40]

I can not answer your question about used ECUs with the proper knowlege, but how do you expect to make sure you get a good one if you cannot test the one you have to make sure that is your problem.

Seems like you should be able to monitor the voltage to ISC to make sure it is there at key on. I take it this voltage is from the ECU, but am not sure what voltage it is.

Then if the ECU is toggling the ground , you should be able to see that happen with a voltmeter hooked to the wires at ISC also as the voltage measured would change when a ground path is provided by ECU.



Edit: I just re read Rods last post and he said it was 12+ but I am still not sure from where is comes from and if the 12 v to the ISC is what burns out if it comes from ECU or if it is just the ground portion that burns out and looses the ability to complete the ground even though 12v+ is still there

[JONSNELL]

Finally !!!!!

Managed to get my hands on a replacement ECU and all is good.

So the answer to my question re the ECU is yes in fact the ECU can give the diagnostic program a signal that it is adjusting the IAC valve but in fact it is not.

Cant say definitively it was the IAC that wrecked the ECU or a combination of that and loose earth wires.

Does anyone know if the ECU can be rebuilt ? If so where ?

Much happier to put this behind me ... on the positive side it has been a good learning experience and thanks for everyone's help.

On a side note I was talking to the mechanic this morning and he said that he has had quite a few failing IAC's lately in F80's and F100's and even replacements have only lasted a couple on months in some cases.

[seahorse5]

On a side note I was talking to the mechanic this morning and he said that he has had quite a few failing IAC's lately in F80's and F100's and even replacements have only lasted a couple on months in some cases.

That must be quite a mechanic that you have there !

The F80 and F100 Yamahas are CARBURETED engines, not fuel injected like your 115 so they do NOT use an IAC on them.

[JONSNELL]

Mate in Australia they are fuel injected