OX66 Throttle Position Sensor Q’s

[fishinAK1]

Good morning (AK time).

I’m having mid to low RPM surging issuesw my 2005 Saltwater Series OX66 200hp. For the full story and diagnostics it’s all in the “OX66LP pumps” thread.
HOWEVER, my current thought is the TPS. When I test resistance, w cylinder 1 disconnected and fully closed, I’m measuring about .9 and fully opened about 4.5.
This seems high on the low end and low on the high end.
Also, when slowly moving throughout the throttle range it’s not a nice steady increase in resistance.
One more thing, the resistance jumps around a bit when I tap on the TPS with my finger.

Questions:
-How can I test voltage of TPS without the having the special wire harness?
-can I expect voltage results to be different from my resistance test?
-Should I attempt to adjust my TPS? It never has been (still has yellow dummy paint on screws)
-is this normal behavior for TPS? (Fluctuations when tapped and not smooth increasing resistance)
-where can I buy the test harness?

Thank you so much for all help and ideas! I hope everyone is doing well able to find and spread a little joy this weekend.

 

[wspitler]

I use the YDIS software and harness as opposed to the harness that only tests the TPS, worked great for me and will be useful in the future. It will show you the TPS voltage and many other parameters. Lots of capability. All you need is a lap top computer to run it. You can see the TPS voltage during any surges. One source:

For Yamaha YDS Diagnostic cable set for Outboard / WaveRunner / Jet boat | eBay

All data can be saved to your computer. Supports all models up to 2020. This kit allows full Diagnostics for your Yamaha engine. Everything you need to get up and running is included (Cable, Easy Install software and the latest data files).

www.ebay.com

 

[fishinAK1]

bummer! Looks like YDS doesnt work for OX66 engines.

"Important: The software will NOT work on Yamaha OX66 fuel injected engines, Yamaha carbureted engine,
or MAC computers!"​

 

[wspitler]

Too Bad! Didn't know that.

 

[seasick]

Only diagnostics are the blinkey lamp.
O2 resistance values at extremes are not bad and are not your problem.
Did you look for and check the filter in the pressure regulator valve n the VST assembly
Trying to be logical; If the TPS seemed to act up at fairly open throttle possible due to a bad spot on the TPS resistor, why would the motor act up at lower throttle?
Did you ever check if there is a screen on the output of the fuel regulator?

 

[fishinAK1]

I have not checked the fuel regulator screen. Mainly because the one time I tried, it couldnt loosen the screws wo risk of stripping. AND I just dont think a that screen could be plugged as I have never had a dirty filter or screen in 10 yrs of ownership. this includes the injector baskets, VST filter, onboard filter, and Racor.

Seasick, Im curious what makes you so sure it is NOT the TPS? At cruising speeds the motor did NOT act up. seemed to run fine, other than losing a little top end RPMS. at mid to low throttle is where the surging is occuring.

Im working on jury rigging a TPS test harness now. will report back with voltage readings...

 

[fishinAK1]

Ok w my jury-rigged test harness I got 0.48 V fully closed throttle, 0.6V at idle, 4.45 V fully opened, and 3.75 V full throttle.
To me these values all seem like they are within spec. except maybe the 3.75 at full throttle. Shouldn't this be closer to 5V? Could this possibly why im losing very top end WOT? maybe I just need to adjust linkage...

So guess Im kinda ruling out bad TPS.

one oddity I did notice, the TPS has an audible click when it clicks on from fully closed SOMETIMES. But sometimes I dont hear the click, but still shows volts. Is this something to consider?

Now what? I guess Ill triple check the VST filter and try once more to remove the fuel regulator. However, if the screen on the fuel regulator were plugged wouldn't that cause a high fuel pressure reading?

 

[seasick]

I have not checked the fuel regulator screen. Mainly because the one time I tried, it couldnt loosen the screws wo risk of stripping. AND I just dont think a that screen could be plugged as I have never had a dirty filter or screen in 10 yrs of ownership. this includes the injector baskets, VST filter, onboard filter, and Racor.

Seasick, Im curious what makes you so sure it is NOT the TPS? At cruising speeds the motor did NOT act up. seemed to run fine, other than losing a little top end RPMS. at mid to low throttle is where the surging is occuring.

Im working on jury rigging a TPS test harness now. will report back with voltage readings...

I am having a very difficult following your issues since you post in three separate threads at the moment. That's why my head is spinning.
First you were convinced it was LP pumps.
Then is was O2 sensor, now it's TPS sensor.
Do yourself a favor and buy the blinky light YB-06765 /90890-06765 ( part number may have changed).
If you have a TPS fault, it will tell you. It will also tell you any pending alarms that haven't been cleared.
When folks on this board suggest a specific test or approach, generally it's a good idea to follow their advice and report back.

Final option: Have a decent mechanic look at your motor It mat turn out less expensive than replacing every part that might be an issue.

 

[fishinAK1]

Seasick, I appologize for the confusion. the reason for the multiple thread is just to make it easier for folks to chime in and not have to read the preceding novel. Guess, I made it more confusing in my attempt. Sorry, I feel like I am following advice and reporting back.

Yes, youre right I have had a number of differnt therories and am trying to rule them out one at a time.
-Not the VST
-Not the TPS (seems to have passed my jury rigged test harness test)
-Not the lp fuel pumps
-Not the fuel injector pump
-Not the O2, (well part of the problem may have been) but now new
-Not the injectors (cleaned and recalibrated). (although they were all running rich, according to Rich Brucato)

Not sure what to look at from here. I did notice that my oil link rod maybe a bit to far the stopper 0.075" (as measured by caliber), but I kinda doubt thats my problem. That wouldve been like that for past 10 years.

I guess as Family suggested, maybe the CDI just needs to learn my new O2.

As far as a "decent mechanic" I dont have the luxury of towing the boat to an infinate number of hungry mechanics. No road access here. and the only 2 Yammi mechanics in town, while very qualified, are busy with a back log of 4 stroke work.

 

[seasick]

No knock sensor as suggested on that motor,
The ECU does not need to learn the O2 sensor. It is not a car

 

[fishinAK1]

Is 3.75 v at WOT the normal?

 

[seasick]

The voltage at full open throttle plate is fine. The lower voltage at basically the WOT position seems a bit low but all that tells me is that the throttle plate may not be opening far enough when the control is pushed forward.That won't explain the surging. Going back in posts you mentioned that the fuel rail pressure did seem to vary a bit. I think instead of looking at every system, you should try to find a fuel delivery issue or 100% prove there isn't one.
First step is to run using a separate portable fuel tank with fresh gas and a new hose connected at the motor (bypassing the main filter, primer bulb and fuel lines and see what happens. Go for a ride and have the fuel gauge connected. If you have issues, then the existing gas, filters, anti siphon valve, primer bulb and fuel lines are probably OK. If there are no problems running, the issue is with the fuel plumbing.