bad TPS??

[majestic rider]

i have an 08 yz450f.bike at idle,on the stand engine surges,making the chain slap wildly.at idle.is this a carb issue?a larger pilot?or i think an TPS malfuntion.do you just disconnect ?its expensive to replace.is it safe for the electrical circuit to leave the TPS disconnected for years?any input on my issue would be very helpfull.thanks. ed

[grayracer513]

Is that on the stand in gear? The chain should slap wildly. There's nowhere near enough rotating mass to make it run at a smooth steady speed under those conditions. Does it surge underway?

[majestic rider]

hey gray.yes running in any gear.ive got an 9.21oz fww on no change.i really cant feel it surge while riding,id say no to that.

[The Spanky]

I don't think you really have a problem, but the TPS is easy to check. It's nothing more than a normally open/normally closed switch. Just disconnect it, and see what happens, no harm will be done.

[bendover932]

i may be clueless but i have to ask.....why would you have your bike idling in gear on the stand to even know it did it ..lol

[majestic rider]

i do it to warm up the chain for lube,and to spin the water off after washing the bike.

[grayracer513]

I don't think you really have a problem, but the TPS is easy to check. It's nothing more than a normally open/normally closed switch.

Pardon me? The TPS is a potentiometer that returns a varying voltage to the CDI so that it can tell where the throttle is exactly. This information is used to alter the ignition timing based on load. It is safe enough just to disconnect it, in which case the CDI defaults to an assumption of a full throttle condition, but it is anything but an on-off switch.

[forklord]

does anyone know what the proper ohm reading would be on the TPS in all outputs?

[grayracer513]

The procedure is to measure resistance in several prescribed conditions, then measure the TPS output voltage while the engine is running. The process is outlined in the manual.

Don't have one?

http://www.yamaha-motor.eu/community/service/manuals.jsp

[The Spanky]

Pardon me? The TPS is a potentiometer that returns a varying voltage to the CDI so that it can tell where the throttle is exactly. This information is used to alter the ignition timing based on load. It is safe enough just to disconnect it, in which case the CDI defaults to an assumption of a full throttle condition, but it is anything but an on-off switch.

I understand that, I was just over-simplifying. The varying voltage tells the ECU to switch ignition curve maps. The ignition advance doesn't vary infinitely, it has two or three pre-programmed settings based on a 3-D map. The end result is no different that just using a two or three position switch. Disconnecting the TPS causes the ECU to default to the WOT map.

[grayracer513]

I was just over-simplifying.

Considerably.

[The Spanky]

Considerably.

Please don't be condescending, it's not necessary. I didn't think that a detailed description of the function of the TPS was really necessary as it clearly isn't related to the (non-problem) condition the OP described. Forgive me father, for I have sinned...?

[grayracer513]

Please don't be condescending, it's not necessary. I didn't think that a detailed description of the function of the TPS was really necessary as it clearly isn't related to the (non-problem) condition the OP described. Forgive me father, for I have sinned...?

It is always helpful to understand as fully as possible how a system is designed to work when you are trying to determine why or if it's malfunctioning. Describing the function of a component as incorrectly as that will certainly not help anyone analyze whether it's working right or not. This forum is supposed to be about information. Oversimplification to the point of misinformation is condescension in its worst form, in my opinion.