2001 SX225 Ox66 Sensor voltage

[Inpursuit]

Well I have been chasing a problem of a rich running condition once the air temp warms up so I checked the intake air sensor and the voltage was out of the range in the manual so I replaced it and the new one is lower yet so my question is does this motor have a common supply voltage to the sensors?

[rodbolt17]

yes the 5v reference is used. check the 5v ref,if its low check the 5v ref on the tps.
also check the coolent temp sensor.
also test rail pressure.if the screen in the regulator is dirty it spike rail pressure and will run rich.

[Inpursuit]

Thanks Sir, I will check those things
This is what i've been chasing,
I have been having a rich condition ever since I got this motor and finally got around to checking what I thought might be the problem.
The problem I'm having is that the motor will run fine in the morning when it's cool but in the afternoon when it warms up it runs very rich so my gut feeling is that the intake air temp sensor may be the problem or at least some of the problem so I checked it per the Yamaha service manual and it shows it should be from 3.4-5.3V with the key on but when I checked mine it shows 2.4V so is that enough of a difference to cause a problem?
I also put a hair dryer on the sensor and the voltage dropped and i'm also wondering if that is normal for it to go down.
Thanks: Frank

[Tucker]

Inpursuit I have the same motors. I'm no expert by any stretch and I've learned much from the shop manual and especially from following rodbolts posts here and on Iboats, the OX66's also have a large following on THT. I can't ever recall reading about a problem with the air intake sensor, not to say it's not your problem. How do you know you have a rich condition? Motor bog? Ever been inside your VST? As the RB said buy the test harness, about $20, and check the TPS. Seems to be one of the first tests to run when a problem like this arises.

[Inpursuit]

The reason I think it runs rich is that when it warms up (air temp) the gas fumes coming in the boat will make you're eyes water (very strong) and it idles rough and misses a little and will stall every so often, usually trying to dock the boat.
I have had everything apart that I can and checked the filters and changed o-rings or gaskets where needed.
My next plan of attack is fuel pressure and function of pressure regulator with a Mity Vac.
Today I checked the sensors listed below,
TPS 4.64 V Ref., Idle .62 V WOT 4.95 V
Intake Temp Sensor 4.64 V Ref., 2.75 V out @ 55 deg
Knock Sensor 4.95 V Ref. and functions per manual
Atmospheric Pressure Sensor 4.95 V Ref., 3.90 V out
Thermo Switch's 185 deg. close, 150 deg. open
Coolant temp sensor in spec with manual

[rodbolt17]

your ref voltages are out of spec.
all the orange wires and sensor wires,other than the O2 sensor, rely on a 5v ref.
if the ref s wrong the signal return is wrong.
have you changed the 3 lift pumps?
needs to be done about every 3rd season as maint.
have you tested the O2 sensor output per the 3 tech bullitens?
the flame test is worthless.
and fuel rail pressure is critical.
there is a filter behind the regulator,if this filter clogs the restriction spikes pressure.
increased fuel pressure means a rich condition.
the ECU doesnt realize the rail pressure increased and opens the injectors for its regularly mapped time.
if the ECU senses low batt voltage it increases injector on time,rich again.

[Inpursuit]

rodbolt,
What directly effects ref voltage and what can be done to correct it?
I have changed the fuel pumps with new yamaha ones but have not run it yet.
How can I get ahold of the tech bulletins for the 02 sensor.
The filter behind the regulator is clean, I went through all the filters and not a spec of dirt in any of them which was kinda surprising.
I am working on putting a guage together to check fuel pressure but wanted to cover the sensors while I try to find the fitting to go on the schrader valve on the fuel pump.
Thanks sir for the info it is greatly appreciated.

[rodbolt17]

on the 3.1L engines there are actually 2 5V ref circuits.
both are generated by the ECU.
any sensor on that circuit can load the circuit down.
however all the sensors can be tested manually with a volt or ohm meter.

[Inpursuit]

Please explain on how to check each sensor, can I disconnect them one at a time and monitor ref voltage and see if it goes up when the problem one is found?

[rodbolt17]

possibly, check your ign timing as well.
may also wish to check the VST vent line for raw fuel. should not have raw fuel in the VST vent line.

[Inpursuit]

I finally got a fuel pressure gauge and it holds at 35 psi after ign is off and will try to run it tomorow.
Is timing something the average guy can check?
Thanks

[rodbolt17]

yes its easy.
what your looking for is about 7* ATDC, make sure you understand ATDC as opposed to 7* BTDC.
if ign timing is 7* BTDC after engine warmup then you have a sensor/ECU issue.
at 7* BTDC engine idle speed will be in the 1200 RPM range.
the ecu will react to a sensor failure by locking base timig at 7* BTDC.
depending on what failed it may advance.

[Inpursuit]

Checked the coolant temp sensor per you're request and it checks to the #'s in the manual.
Any advice on checking the sensors other than checking them with the key on and hooked up?
If the timing was advanced would it idle @ 1200rpm all the time, last time I ran it it idled at 750ish in neutral.

[99yam40]

sounds like you are trying to confuse the issue or us.

If ECU is seeing a failed sensor as he said it will react

[Inpursuit]

Well i'm not trying to confuse the issue, the issue is confusing me.
What i'm looking for is how to best check the sensors.