ISC testing - F225 TXRD

[fairdeal]

So today I hooked up the YDS to use the "Stationary Test" for the ISC and make some other observations with VOM and test light.

Boat is on the dock, didn't want to bother hooking up water, so this was just "key on" - no running.

The F225 ISC has, as has been discussed, 2 power leads, each supplying two coils - analogous to this:



So - first observation:

- at "key on" - two of the coils - one "side" of each hot lead - are continuously grounded by the ECM. ("S1" and "S4" on the diagram)

(I have noticed on prior occasions that, if I'm letting the engine sit with key on but not running- the ISC will get nearly "painfully hot".

I measured the coil resistance the other day: ~32 ohms. So with power continuously applied, that's two 4.5 watt (12 volts x .375 amps) "heaters" )

Does this "continuous ground" stop once the engine is running? I assume so...

Moving on to the 'Stationary Test" - which as stated by the YDS program - lasts for 3 seconds - here is a video (test repeated 3 times)

https://vid.me/U4J6

What I assume I'm seeing:

the "Stationary Test" moves the valve to "full open" -

"holds it open" by continuing to apply electrical pulses -

then finishes by bringing it back toward closed.

[fairdeal]

I then disconnected the valve,

connected a 4.5 watt incandescent test light

between a hot contact and a coil contact,

and ran the "Stationary Test" (3 times)

As the videos show, the lamp "flickered" as the ECU "pulsed" the ground.

(Of course, for the two coils with "constant ground" the bulb was already lit before "flickering" - then went back to continuously lit)

One of each "side"

https://vid.me/q9rf

https://vid.me/wpJQ

(I also tried using the Hertz function on the VOM - but got no reading)

[99yam40]

still makes me wonder what regulate the pulses
Time or something other that time?

but seeing as the ECU does not monitor if the unit moves when told to, then it must just pulse until it see other things change i guess.
when the ECU gets happy it stops pulsing

[fairdeal]

well, here's my "very general" understanding:

the valve has 120 steps between closed and open

the rattle we hear at shutdown is the ECU sending "many more" than 120 pulses

- in the "open" direction -

to ensure that at startup the valve will be open

Then at startup, the ECU - "knowing" (assuming) that the valve is open -

"counts" down - and up - "keeping track" as it controls the valve


Now, having said that -

- how is it that when I ran the "Stationary Test" that the valve opened more -

and then reversed toward close?


and it doesn't explain how a "bad" ("stuck"?) ISC causes the ECU to overheat and die....

[99yam40]

I have a feeling they did not set up anything to keep track of where it is, if they did they would not have to assume it was at the wide open spot or have to pulse it so many time to try to make sure it should be

[pstephens46]

Is it 100% open or closed at start? Rodbolt mentioned the ISC is responsible for the rpm jump at start, especially 250hp and higher?

[fairdeal]

Is it 100% open or closed at start? Rodbolt mentioned the ISC is responsible for the rpm jump at start, especially 250hp and higher?

You're right, it makes no sense that it would be "100%" closed (0% open) in the "key off" position.


I'm not sure what I'm seeing in the movement of that "Stationary Test".

Clearly its going from from "not 100% " to "100% open" - and back to "not 100%".

I'm remembering now that - although I could barely read the laptop screen in the sun -

the screen kept indicating - I think it was - "67%" after each test cycle

I didn't think to save a screenshot - here is the test screen from the manual:

(I was too busy holding the camera to watch during the test)



So perhaps the "parked" position on my engine is 67%?

and after the test takes it to 100% - it returns to 67%?

If thats' the case, the only way I can see the valve 0% open is with the "Active Test" ?

[pstephens46]

I have only used my YDS twice. I think I may play with it this weekend. The ISC is a chattering thing isn't it? You would imagine it would be a smoother running device on a Yamaha. Sort of like speedometers and other guages that use stepper motors. Wonder what Rodbolt has to say about these percentages? I have no clue.

[rodbolt17]

remember folks.
the ECU does NOT and CANNOT monitor the physical position of the valve.

the ECU opens the idle air valve to 100% at engine shut down cause the ECU is programmed to anticipate another engine start after that shut down.
will it be a COLD restart?
will it be a HOT restart?
that is far beyond the ECU's programming.

so the engineers that set up the computer map simply programmed it to go full open.

at a start cycle the ECU defaults to a set timing,injector on time and the ISC at 100%.
this insures a restart hot or cold.
it also typically starts at about 1000 RPM.
once running the ECU then gathers various information from various sensors and corrects the idle.
hence the term Idle stabilization control, the rest of the world calls it Idle air control.

the later F250 and up do not use the ISC,the ecu controls throttle angle directly.

but sometime, try unplugging an injector or grounding a plug lead and see what the ISC does.

[fairdeal]

the ECU opens the idle air valve to 100% at engine shut down cause the ECU is programmed to anticipate another engine start after that shut down.

Rodbolt - are you able to see my video of the "Stationary Test" on my F225?

https://vid.me/U4J6

The "starting" - and ending - position seen there in the video,

is what I find the valve at whenever I remove it with the engine off.

If it is NOT then, during the "test" opening even more - what IS it doing?