2003 F115 IAC vs ECM

[boscoe99]

there is still the mystery of why, in the manufacture of the valve,

is it advantageous to have two separate pins for (+)

each of which "internally" splits to supply two coils

rather than one power connector common to all four....

Found this on you tube. It explains different ways is which the coils of a stepper motor can be arranged.

https://www.youtube.com/watch?v=ZEcQW5rCbSQ

The engineers can argue till hell freezes over as to which configuration is the better. See Ford versus Chevy or two stroke versus four stroke.

[boscoe99]

Calling mr. fairdeal, calling mr. fairdeal,

How about you measuring the current flow through your ISC valve while the motor is running to see what is to be seen.

Does current flow through both red/yellow wires at the same time or not?

Is the current flow equal through both red/yellow wires at all times or not?

What is the current flow through the red/yellow wires?

Follow on questions to follow.

[rodbolt17]

current DOES not flow all the time.
only when the request % changes.
if current flowed through both at the same time the stepper would most likely burn out as it is now commanded in both directions at the same time.
one set of motor windings turn it in the other set turns it out.
excessive current flow can overtemp the ECU.
can be a bad ISC or a low speed engine miss that the ECU is trying to compensate for.

if you don't belive me next time your running an EFI motor with an ISC simply unplug an injector and watch what it does.

[boscoe99]

I know that a defective valve can damage the ECM. Which Yamaha engineering also knows.

Wondering why Yamaha did not design the system so that the ECM drives an electronic relay (miniscule current flow in the control circuit) which in turn drives the valve so that if and when the valve fails the ECM is not damaged.

Back to the drawing boards you defective Yamaha engineers.

[rodbolt17]

that I don't know.
cost maybe?

I do know a physically stuck ISC on an F225 can fry the ign coils,melt the coil holder and then fry the ECU.
can also happen with a clogged fuel injector.
if your meter has an Hz function you may be able to see a request change briefly as a frequency.

the rattle you hear at shut down is the ISC opening to the 100% request in anticipation of the next start.

that is why most EFI motors flare up at start then settle down.
takes a bit for the ECU to decipher all the sensor data.
now why the F250-F350 motors start so violently? I have no clue.

[fairdeal]

Calling mr. fairdeal, calling mr. fairdeal,

How about you measuring the current flow through your ISC valve while the motor is running to see what is to be seen.

Does current flow through both red/yellow wires at the same time or not?

Is the current flow equal through both red/yellow wires at all times or not?

What is the current flow through the red/yellow wires?

Follow on questions to follow.

Coincidentally I had the ISC off just the other day to play with it.

Only things I learned so far:

1. each of those 4 coils has a resistance of ~32 ohms

So if Ohm's Law applies....

2. If you apply power to any one of them, you get one "step" - that's all.
Must have to alternate coils to get it to keep moving.

[boscoe99]

The actual stepper motor part seems to be straight forward. The control for the motor is something altogether different.

As the motor "stepped" with the application of current, how did it respond when the current was removed? Did it stay where it was or did it return to the position before power was applied?

[99yam40]

Good questions I guess,
but what happens when power/ ground is applied but not removed would be another one.

I am not sure how they make the stepper motor switch between the steps.

does the system hit it for a short time and then stop, or hit and then something tells it when to break the ground when it gets to a point

[fairdeal]

The actual stepper motor part seems to be straight forward. The control for the motor is something altogether different.

As the motor "stepped" with the application of current, how did it respond when the current was removed? Did it stay where it was or did it return to the position before power was applied?

IIRC I felt a slight "twitch" when contact was made, a corresponding movement of the plunger -if there was one - was too slight for my old eyes.

Did not feel anything when power removed so I assume there was no backward movement.

I just watched that youtube video from the link above; very interesting.

My takeaway is that the motor requires pulses of current, not continuous,

and a second coil with a "staggered" pulse to make it turn.

So the ECM must be "momentarily" grounding the coils in an alternating pattern to move the valve -

[pstephens46]

I believe Mr Rodbolt said the new digitally con*****ed motors do not have the ICV? Since the throttle is con*****ed by a servo?

[boscoe99]

I believe Mr Rodbolt said the new digitally con*****ed motors do not have the ICV? Since the throttle is con*****ed by a servo?

At this point in time there are older model Yamaha's (dating back to the 2005 F250) that use an electronic throttle valve without an ISC valve and then there are some of the latest models (F150XB for example) that still use mechanical throttle bodies with an ISC valve.

But yes, it appears that all of the DEC (electronic throttle/shift) con*****ed motors use an electronic throttle valve without an ISC valve being employed. With some of the mechanically con*****ed models also using an ETV and no ISC valve.

Pity the poor mekanic trying to keep up with it all.

[boscoe99]

if you don't belive me next time your running an EFI motor with an ISC simply unplug an injector and watch what it does.

What happens? If the engine is at an idle and fully warmed up I am thinking that the valve will remain fixed at whatever position it happened to be in when it was disconnected. No change would be seen with respect to engine operation unless and until the throttle position was changed.

Since the ECM does not monitor the valve I am guessing that maybe a check engine light won't illuminate. Unless the ECM is just smart enough to know when the valve is disconnected.

Fairdeal, what do you see?

Too bad that all of this is not thoroughly explained in a Yamaha service manual. ISC valve are known to get gunked up and cause operational problems. The SM does not address the cleaning of the valve that I can find. Why not?