1993 Yamaha L250 txrr idle stuck at 1200 rpm

[AS19-1]

1993 Yamaha L250 txrr While out catching bait the other day engine was in neutral idleing around 700 then all of a sudden rpm increased by itself to 1200. Turned the motor off and back on but idle will not drop down. When I tried to run home the engine wouldn't go above 1800 even at wot. I idled back to the dock. I thought fuel pumps might be an issue and they had not been replaced in a while so I changed all three with new assemblies and a new 10 micron racor. Engine fires right up but still stuck at 1200 rpm. I have done a lot of searches but couldn't find much on non EFI motors. Thermostats are less than three months old so I dont suspect bad thermostat and am in Miami where the water temp today is 76. I don't have the winky blinky and am on a tight budget any help would be appreciated. Can I test knock sensor with a fluke meter, what do I set it for and what readings would I be looking for. Thanks again

 

[rodbolt]

Re: 1993 Yamaha 250 trxx idle stuck at 1200 rpm

Re: 1993 Yamaha 250 trxx idle stuck at 1200 rpm

as there is no such thing as a 1993 TRXX motor all we can assume is you have a carbed 3.1L 250.
any sensor failure and some out of range failures will lock timing at 7 degrees BTDC causing high idle(1100 RPM)some failures mean top speed cannot be reached.
all sensors on that engine can be tested with a DVM and the service manual.
always test the 5V sensor reference voltage before condeming sensor outputs or a sensor.
that engines ECU actually has 2 5V reference orange wirescoming from the ECU and uses 2 5VDC powersupplies in the ECU.

 

[AS19-1]

Re: 1993 Yamaha 250 trxx idle stuck at 1200 rpm

Re: 1993 Yamaha 250 trxx idle stuck at 1200 rpm

Sorry model # L250txrr year 1993. Any sensor in particular? It does not let me accelerate kind of like safe mode when alarm is going off but no alarm now. Is knock sensor failure common? The knock sensor looks old probably original. Would you happen to know off hand what voltage knock sensor should be giving me if good or bad. Thanks for the help.

 

[rodbolt]

Re: 1993 Yamaha L250 txrr idle stuck at 1200 rpm

now that I have your attention.
almost any sensor,TPS,Coolent,Knock, and even a bad electric enrichment pump can lock timing.
your system uses two basic systems to make spark at the correct time at a given RPM.
it uses 6 pulser coils to trigger spark.
a two coil staator to charge the capacitors in the CDI unit to produce primary voltage to the ign coils.
the ECU reacts to various sensor inputs to CONTROL spark.
and yes your motor exists, its a left hand whith trim,25 inch shaft and remote control, the last R indicates its a 1993 model.

the rest will be up to you.
knock sensor issues are rare but easy to test with the correct service manual and a DVM.
YOU MUST have a correct manual and a DVM and sometimes an old school analog meter to test this system.
without it your shooting blind.
have you checked the ign timing at idle and checked the coolent temp sensor as well as the crank position sensor and the throttle position sensor.
remember that engine has 2 coolent temp switchs and 1 coolent temp sensor.
the switch will set an alarm the sensor can cause increased idle but top speed can be reached.
the TPS or CPS will increase timing and top speed cannot be reached(timing locked at 7 degrees BTDC).
knock sensor is about the same if its failed or unplugged.

 

[AS19-1]

Re: 1993 Yamaha L250 txrr idle stuck at 1200 rpm

Rodbolt thanks for the replies. I made it over to the boat today and tried testing the sensors with my dvm Fluke 111. My CPS checked out OK according to the specs. The knock sensor however did not give infinity (OL) it was reading .585 does that mean it is bad? I also have a question on the TPS (please forgive my lack of knowledge) I unplugged the TPS and checked resistance between orange and red and I got 4.9 K ohms which is in spec. Now here is where I am confused. The book said I should read .47 -.51 volts between pink and orange with flaps closed. My meter will only give me a reading for this on the diode setting is that the right setting? On that setting it gave me a reading of 1.56 - 1.75 that was the full range of adjustment by loosening the screws When I advance the throttle the numbers would change downward. Really confused on what setting for TPS. Now if we could go back to my knock sensor not reading infinity does that mean it is faulty for sure. Thanks for helping me out with this.

 

[AS19-1]

Re: 1993 Yamaha L250 txrr idle stuck at 1200 rpm

Just realized of course I didn't get a reading on DC volts because I was testing sensor side of plug with the plug undone (brain fart). So know I understand it must be tested with sensor plug connected. Since this is the case do I need to determine my knock sensor is bad and was the culprit before adjusting tps and setting correctly

 

[AS19-1]

Re: 1993 Yamaha L250 txrr idle stuck at 1200 rpm

This morning I took out my knock sensor and cleaned it up with a wire brush and retested and got infinity. I screwed it back in set the tps and she fired right up with normal idle. Took the boat out and ran around for an hour no problems. A little worried the knock sensor will fail again. There was just one spot of corrosion by the threads that I cleaned could that have been the problem do they ever fail intermittently? Thanks again

 

[rodbolt]

Re: 1993 Yamaha L250 txrr idle stuck at 1200 rpm

ok
on the knock sensor.
its a piezeoelectril cystal device.
means if you shake it it shocks and if you shock it it shakes.
its a single wire device that grounds through the sensor body.
the ECU sends a constant 5Vdc signal to it.
if the sensor seat becomes corroded or the sensor is loose the ecu will see a loss of the sensor and default to 7* BTDC idle will be high and top speed cannot be reached.
in normal operation the ECU monitors that 5V signal and at a knock condition the block vibrates.
this vibration shakes the crystal resulting in an AC output riding on a DC signal at a specified frequency that the ecu will detect as knock.
resistance tests on that device is futile.
try using the test in the manual.
sounds like most likly you either had corrosion at the connector or the sensor to head connection(ground path) was dirty and the ECU saw it as a dissconected sensor or a sensor failure and did exactly what it was programmed to do.

on the TPS
now that you monkeyed with it it MUST be reset correctly.
the throttle shutter on the carb that drives it MUST be fully closed not at idle setting.
dissconect the linkage to that carb to reset it.
must be done with key on engine off and sensor connected to the engine harness.
should be .47V plus or minus .o1V.