2006 F90 ISC valve - for Boscoe

[fairdeal]

pulled the covers off the 2006 Mercaha EFI 4-stroke - or should I say Yamamerc F90
and looked at the ISC

its a four-wire - - seems this part was used only on the F75 and F90



as one would expect, there are two coils - each reading about 30 ohms

[fairdeal]

not surprising - at key on, one coil pair had power to one lead, and ground on the other:



and was drawing ~ 0.3 amps

[fairdeal]

but this was surprising:

at key on, both leads to the second coil showed ~8V !



it appears - from the Merc SM (I don't have a Yamaha version) -

that all four leads connect directly to pins on the ECU:

[rodbolt17]

at 8V on bothe pins it will lock the rotor shaft.
it is NOT a yamamerc.
Yamaha built the merc f115 and the F200/225 back in the day.
merc built the Yamaha f25 and F40.

exactly how the ECU is wired inside or how it is mapped is appearently top secret cause it is published nowhere.
all I know is I can test it.

[fairdeal]

so in terms of "watching the valve work" -

I know I can parallel an LED to the ground side of coil #1

but I'm momentarily baffled by what I'm seeing on coil #2...



I'm fairly confident that when the valve moves, one lead gets 12v and the other grounded -

but why is the ECU apparently putting 8V on both of them when the valve is static?

[fairdeal]

hey good morning Rodbolt!

but what do you mean, "not a yamamerc" ?

[rodbolt17]

back in the day mercury marine and Yamaha worked on the 4 stroke models as a joint venture.
started back about 1993.
in 2003 merc sued Yamaha for unfair practice.
they lost.
the marriage ended in divorce in 03.
since 03 mercs are not anywhere connected with Yamaha or Yamaha cconnected to mercs.

[boscoe99]

but this was surprising:

at key on, both leads to the second coil showed ~8V !



it appears - from the Merc SM (I don't have a Yamaha version) -

that all four leads connect directly to pins on the ECU:

The Mercury manual agrees with Yamaha data with respect to the use of a four pin ISC valve and the wire colours. The Mercury manual would have more detailed information as to the actual operation of the valve than would the Yamaha manual. I suppose anyway.

[99yam40]

If both leads on the second coil read 8v, to me that would mean the ecu is only sending 8 volts to it and the negative/ground in the ecu is not made up.
I am guessing the negative meter lead is on a motor ground connection
is this while coil is hooked up to ecu?
does not look like it in the pics unless you have a test harness hooked up. if not testing with coil hooked up you would not read thru the coil

If I get what Rodbolt wrote about both having 8v would lock up the rotor, maybe he meant if both coils received 8 volts it would lock the rotor not both leads on one coil.
At key on you are showing 12v on one coil and 8 on the other.
ecu is grounding the one with 12v so you read nothing between ground and the grounded pin

[Angelo4730]

I own a 2005 Yamaha F90 TLRD and I have a bad ISC valve, so I am in the market to buy a new one. Can I buy an equivalent "mercury" ISC valve that looks the same? It is my understanding that Yamaha makes these for the mercury 90 hp engine that Yamaha used to manufacture. The reason I ask is because the mercury part is over $50 cheaper in price even though I think it may be the same part.

Thank you

[fairdeal]

I would hesitate to identify a part simply because it "looks the same"
but certainly parts are available with a Mercury label for those engines which were in fact made by Yamaha.

Specifically for the ISC, I happen to know that Mercury part 880883T02
is identical to the Yamaha 6D8-13105-00-00 used on the 2005 F90

there is one available on eBay:

Mercury 880883T02 Control Valve / Yamaha ISC 6D8-13105-00-00 6D8-13105-01 | eBay

[boscoe99]

Diagram added.

[fairdeal]

Diagram added.

thank you, boscoe.

it was interested that Rodbolt was familiar with the practice of applying the same voltage to both ends of the coil to "lock it".

I'm not sufficiently smart or educated to discern how that acts differently
from simply having one end connected to ground, and the other "unpowered"
it certainly requires a more complex system to provide

and in total Yamaha used 4 pins of the ECU for the valve -
when I would have thought they would only need 2 -
one to ground each of the coils

so speaking of ECU -
Rodbolt unnerved me with his concept that in 2005,
without Yamaha's cooperation, Mercury was "cloning" F90 powerheads
maybe I will start a new thread...

[99yam40]

Just in case you do not realize it ,if you apply a voltage to one side of a coil with the other side open ended, both sides will read the same voltage.

[fairdeal]

if you apply a voltage to one side of a coil with the other side open ended, both sides will read the same voltage.

interesting point, 99
the 8v was measured at the wire connector terminals - detached from the valve coil

but that means I was measuring directly the pins on the ECU - and who knows exactly what solid-state circuitry is inside there