The Yamaha Road Star Warrior Forum

TPS - Throttle Position Sensor.  This is a rheostat (variable resistor) that sends a signal to the ECU based on the position of hte throttle.  The TPS is attached to the right TB.  If the TPS is faulty, the ECU won't get the proper signal.  Worse case scenario is that the bike won't run. 

CPS - Crankshaft Position Sensor.  This is a magnetic device that measures the speed and postion of the crankshaft and tells the spark plugs when to fire. 

Since the CPS is a simpler device than the TPS (it has no moving parts, only the crankshaft moves; the TPS does have moving pats), I'm assuming the TPS is more likely to cause this problem.  The only way I could see the CPS causing a problem is if the frequnecy of the engine's vibration in this RPM range is shaking wires loose or causing the CPS itself to vibrate.

SWODude .... i realize that this is also a discussion forum and we are all entitled to contribute   ....

IMO, it behooves you to read this topic and the enclosed hyperlinks within it: Engine Sensors 101 - Extracts fr Chapter 1 - Hyperlinked

Sensors are input devices that send information or feedback to the ECU. They are not decision makers.

The ECU makes decisions based on the inputs and triggers the outputs, such as the injectors, coils, relays etc.

The CPS is a reluctance device that generates a voltage that is inputed to the ECU. Without this info the bike is stone dead in the water.

The common failure of the TPS is a flat spot in the resistor windings as the TPS wiper passes over the area causing an erratic signal to the ECU. The factory recall bulletin has the details.

Bottom line, i can't ever remember reading about any member being stuck on the side of the road for a so called confirmed defective TPS.

On the other hand, many a member can attest to being stranded on the side of the highway or a near fatal episode while riding because of a failed CPS which have come in many many different flavors than you have described here

A cracked CPS wire can create intermittent engine problems that might be perceived as a faulty TPS w/o displaying any fault code!

Thanks.  Would a cracked CPS wire create flat spots in certain RPM bands?  As soon as I get everything back together (TPS installed and aligned, ensuring that the TB plates are aligned, making sure the fuel line isn't kinked up, etc.), I'll go back to my PCIII and try increasing the values for the 1500-2000 RPM range, because it seems like it leans out there.  It might be that simple.  I was thinking a TPS issue because it felt like there was a delay between rapid throttle changes and the fuel/air mixture catching up (i.e, opening the throttle seemed to momentarily lean out the mixture). 

i wouldn't rule the TPS out just yet, it definitely can go bad as described. it can have a "flatspot" where it kinda hangs on a certain position and then jumps as you accelerate.i replace a fair amount of TPS's on outboards(but that's different i know)

the reason they go bad on boats is 'cause the throttle stays in a certain position for long periods of time where on a bike they move all over alot more wearing the contact down equally.

i have to admit though i haven't heard of any TPS's go bad on bikes but then again i'm a newbie biker,lol

however i think if the TPS  goes bad, some engines (i'm not sure about the warrior) will run off of the MAP sensor only. it won't run as good but it will run.you can check it by checking the voltage and slowly increase the and decrease it and see if it "hangs" anywhere.

i wouldn't think the CPS would have a flatspot at a certain rpm , it would do it all over the rpm range.

Ok.

I got the part, but I'm still confused.  I got the TPS with the new part # today.  I tested it, but it only has about half the resistance, maxing out at 2.36.  I adjusted it so the min is at .32 and with WOT, it reads 1.82.  Anyway, I thought, "what the hell," so I went for a ride. 

A couple things I've noticed:

-Cold starts are much quicker.  Instead of going through 3-5 rotations, it fires up after about 1-2 rotations.

-Driveability at low speeds is much better.  The throttle response, at least in the low ranges, is much more precise and manageable.  The engine isn't surging in U-turns, even at lower speeds in 2nd gear.

-Freeway driveability is also more manageable.  I can run over bumps, potholes and RR tracks without the engine going lean and coughing through the TB's.  I can, however, produce the cough if I rapidly engage the clutch in upshifts (i.e., sloppy shifting").

Should I be concerned that the measure resistance is that much lower?  My response is fine when I test the throttle with the PCIII connected to the laptop.

I don't have my manual with me so can't check resistance values, but it sounds like huge improvements in ride quality resulted.  If there are no new negatives introduced with the repair then do what I do: go for a ride and smile!

That's what I'm doing.  Riding and smiling!  I still need to tweak my map a bit, I think.  I'm probably going to need to cry uncle and get a custom one done.  I'm curious about how the part number AND the resistance values would change.  MotorsportsSuperStore has the part listed under a new number.  I got the part with the new number.  The part is different AND has different values.  The service manual tells me the max resistance should be 4-6 kOhms.  The new part's max resistance is 2.36 kOhms.  The WOT value is 1.82 kOhms.  But the bike is running okay.  I'll be checking my plugs to see if the engine's running lean.  So far, it seems okay, though I still do get the knock when I ride it up my driveway into the garage.  My low speed rideability is definitely better.

After about 15 days at the dealer, my bike came back with the TPS and CPS recalls done...apparently. 

Dealer:  Your bike is done.

Me: Did you notice the sputtering at 1400 to 1900 rpm?  Do you think I need my thottle bodies sync'd? 

Dealer: Sputtering, could be bad gas.

Me: You did test ride it...right?

Dealer:

Yeah, so they didn't test ride it.    I guess I was going to be their guinea pig.  Even though the Star Motorcycle specialist said to not ride the bike until it was done, I never did trust a young mechanic.

When I talked with them , they didn't stamp my VIN number and they didn't even know I had a PCIII.

The bike feels like crap, I can't believe they gave it back to me like this.   I have to reset the throttle position, tires feel flat, and I have to call Star motorcycles again to be sure they did anything.