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Old 2 Weeks Ago
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Default Crank Position Sensor (CPS) Question

Engine is a Yamaha 2004 150 hp TXRC. Not sure how to read the table in the Mechanics Manual. CPS voltage across leads reads 1.3 VDC @ 1,500 rpm. Table appears to show that this should be 5.5 VDC. Not sure what the table headings of 'Circuit', 'Loaded' and 'Cranking' signify. I'm assuming that, at 1,500 rpm (out of gear and on muffs) that the voltage across the CPS unit should be 5.5 VDC and that @ 1.3 VDC, I need a new unit. Volt reading was taken as per manual with leads remaining connected to CDI.
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Old 2 Weeks Ago
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Does your 2004 150 have any letters before the 150 like F, LZ. SX, or a Z?
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Old 2 Weeks Ago
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Nope; engine model reads 150 TXRC.
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Old 2 Weeks Ago
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How about the exact model and Serial number off the transom bracket...that would be helpful. We could then look at the service manual for your engine and see what it says.

Thanks
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150TXRC. 2004 model year. Carburetted.
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Old 1 Week Ago
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Serial #6G4X1009702P. That is correct: engine is carburated 2-stroke, oil injected. Sure appreciate the help.
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Old 1 Week Ago
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are you using a PEAK reading meter or a meter that shows RMS?
makes a HUGE difference.
if you lose the CPS on that motor you dump spark on cyl 2 and 5.
methinks your hunting sasquatch.
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Quote:
Originally Posted by Psalm 99 View Post
Engine is a Yamaha 2004 150 hp TXRC. Not sure how to read the table in the Mechanics Manual. CPS voltage across leads reads 1.3 VDC @ 1,500 rpm. Table appears to show that this should be 5.5 VDC. Not sure what the table headings of 'Circuit', 'Loaded' and 'Cranking' signify. I'm assuming that, at 1,500 rpm (out of gear and on muffs) that the voltage across the CPS unit should be 5.5 VDC and that @ 1.3 VDC, I need a new unit. Volt reading was taken as per manual with leads remaining connected to CDI.
First, are you using a peak voltage reading meter or do you have a peak voltage adapter attached to a regular voltmeter?

Even though you are actually measuring AC volts the meter is set to the DC scale.

Loaded means the sensor is connected to the engine harness. Unloaded means the sensor is disconnected from the engine harness.

If the voltage is low reverse the leads and test again. A CPS that reads on the low side does not automatically indicate that the CPS is the source of a particular problem. What problem are you having?
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CPS voltage @ 1500 rpm: Peak: 1.4 MV with leads either way (loaded). I'm trouble shooting the CDI inputs after engine began reverting to RPM reduction mode. Have verified correct operation of all three thermal sensors, oil tank liquid level sensor, stats, and battery voltage is fine. All grounds are cleaned and re-assembled. Haven't had boat on water to fully test and problem may have been solved. Last thing I noted as going through the CDI was the CPS so it was also tested per manual. Sure seems to be faulty (MV??). Would have been easier if I could have gotten a Yamaha CDI diagnostic tool (Yamaha part #YB-90890-6765) but such a device is 'unavailable' per vendor's inventories.
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Quote:
Originally Posted by Psalm 99 View Post
CPS voltage @ 1500 rpm: Peak: 1.4 MV with leads either way (loaded). I'm trouble shooting the CDI inputs after engine began reverting to RPM reduction mode. Have verified correct operation of all three thermal sensors, oil tank liquid level sensor, stats, and battery voltage is fine. All grounds are cleaned and re-assembled. Haven't had boat on water to fully test and problem may have been solved. Last thing I noted as going through the CDI was the CPS so it was also tested per manual. Sure seems to be faulty (MV??). Would have been easier if I could have gotten a Yamaha CDI diagnostic tool (Yamaha part #YB-90890-6765) but such a device is 'unavailable' per vendor's inventories.
Here is the DVA I use....works well.

https://www.amazon.com/dp/B00R3B6HYW...detail_1?psc=1


Rodbolts words: "are you using a PEAK reading meter or a meter that shows RMS?
makes a HUGE difference.
if you lose the CPS on that motor you dump spark on cyl 2 and 5.
methinks your hunting sasquatch."


From what you are saying....


"engine began reverting to RPM reduction mode" Maybe it was not going into RPM reduction at all, BUT instead it is dropping two cylinders as Rodbolt says will happen if the CPS fails.....making the engine FEEL like it is in RPM reduction.
Attached Images
File Type: jpg DVA.jpg (106.1 KB, 2 views)

Last edited by panasonic; 1 Week Ago at 05:07 PM.
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Old 1 Week Ago
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That makes a lot of sense as the CPS is definitely out. I think we've gone full circle on this and a new CPS is on order. Again, many thanks for the good advice.
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Old 1 Week Ago
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methinks your gonna have a spare CPS.
I would have spent my coin on a Kv tester and checked the KV on cylinders 2&5 and when I saw I had ign coil secondary voltage I would have continued testing.
verify the audible is working.
anything that will cause RPM reduction will also sound the audible.
if the alarm works but does not sound your not going into RPM reduction.
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Old 1 Week Ago
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Received & installed the new CPS today. Pretty fast service from boats.net. Running engine on muffs. Engine started right up with new unit and CPS delivered 7.73 peak VAC @ 1500 rpm. Engine running noticeably smoother. Removed new CPS unit and re-installed old unit. Old unit reading no voltage @ 1500 rpm with increased vibration. Faulty CPS unit definitely was a problem. Put new unit back on engine & looking forward to going out. Not sure but also not too worried due to the voltage generated by new unit being significantly higher than manual (7.73 vs 5.0).
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Quote:
Originally Posted by Psalm 99 View Post
Received & installed the new CPS today. Pretty fast service from boats.net. Running engine on muffs. Engine started right up with new unit and CPS delivered 7.73 peak VAC @ 1500 rpm. Engine running noticeably smoother. Removed new CPS unit and re-installed old unit. Old unit reading no voltage @ 1500 rpm with increased vibration. Faulty CPS unit definitely was a problem. Put new unit back on engine & looking forward to going out. Not sure but also not too worried due to the voltage generated by new unit being significantly higher than manual (7.73 vs 5.0).
Sounds like you found the "sasquatch" you where hunting....you are now famous.

Hope it works well when you try it out on the water.
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Old 1 Week Ago
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7.3 peak VAC.
what the ell?
peak is supposed to be a DC reading.
we are not looking for AC volts.
RMS is NOT peak.
RMS is about 70% of peak.
also known as WVDC.
I hope it works.
would be maybe the second CPS I have ever seen failed.
it is a simple coil of wire fed a small current looking for a single flywheel tooth to pass to generate a small voltage so the ECU marks it as a crank position.
if you look at it with an ocillioscope you would see a basic square wave signal.
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