Throttle Position Sensor (TPS) bad?

[psi4power]

My bike has been running funny lately. At about a quarter throttle the bike surges pretty bad as if the engine is running lean. These symptoms have gotten worse and worse the past few months. At first I thought it was the pilot jet and air/fuel screw settings but I'm pretty sure it is not since I have set the carbs per Eddie's specs. Currently the bike has the 3X3 mod and full Ti exhaust. I have since checked the petcock and the float level but both are functioning correctly. I then checked the tps and it seems as if its not within spec. With the throttle fully closed it measured 4600 ohms and fully open it also measured 4600 ohms. The book says it should read 78% of the closed measurement when the throttle is open. Could the tps cause these types of symptoms? What does the tps do? Please help!!!

[Wayward Son]

just unplug it and go ride.

[psi4power]

Eddie, do you think this is my problem or is it something else?

[Wayward Son]

possible,but unplugging and riding will tell you.if its cured,just leave it unplugged and go about your business.

[smcdonn]

Just unplug it and then tell US whether it's the problem or not. Seriously, unplug it and go ride it.

[yyzmxs]

What exactly is the purpose of TPS on this bike?

[eddie odell]

What exactly is the purpose of TPS on this bike?

The purpose of T.P.S. on bikes in general can be:

1. Alter the ignition curve based off of engine load. (ours are bogus).

2. Control servo or stepper motors for the purpose of exhaust valves in exhaust systems or other remote devices.

3. Traction control.

4. A reference voltage signal sent to the ECU to be used in concert with other input data for the ECU to make various decisions; ie fuel injection.

5. Can be used to arm or trigger solenoids or anything you want.

5. I use my own TPS strictly as a means of knowing where the throttle is accurately at all times while tuning so as not to guess, ie 1/4, 1/2 etc.

[William1]

Retards timing slightly for emissions reasons, also assists in making a very slow idle steadier. I set my idle to 1,800 rpm and it is fine. Higher idle also reduces the propensity for a bog and piston slap, win-win.

[yyzmxs]

Thanks for the info. I kind of know what it can do on EFI bikes, but wasn't sure other purpose on carbed bikes.

So particularly on DRZ the only reason is/can be "retarding timing". You mentioned higher idle speed. How do you verify your idle speed? I don't like the guessing method. Do you have an aftermarket tacho clock fitted in?

[eddie odell]

Thanks for the info. I kind of know what it can do on EFI bikes, but wasn't sure other purpose on carbed bikes.

So particularly on DRZ the only reason is/can be "retarding timing". You mentioned higher idle speed. How do you verify your idle speed? I don't like the guessing method. Do you have an aftermarket tacho clock fitted in?

If you were talking to me, yes I do

http://s654.photobucket.com/albums/uu266/omandrz/?action=view&current=DSC03702.jpg

[William1]

Thanks for the info. I kind of know what it can do on EFI bikes, but wasn't sure other purpose on carbed bikes.

So particularly on DRZ the only reason is/can be "retarding timing". You mentioned higher idle speed. How do you verify your idle speed? I don't like the guessing method. Do you have an aftermarket tacho clock fitted in?

Both an aftermarket instrument (The Vapor, like many do). I also have some stand alone diagnostic tools that check RPM. You bike, if the fuel screw is perfect, can idle as slowas 800 rpm, which is painfully slow, your bike would be bouncing at that speed. Set it fast, then adust it just a tad less than fast.

I know this is tough to know when you have nothing to go by. If you have a reasonably decent dealer, they can pop the shop tack on and let you get a idea what the speed is and what it sounds like.

[2WYKD]

Who has removed the TPS completely from their carb?

[eddie odell]

Both an aftermarket instrument (The Vapor, like many do). I also have some stand alone diagnostic tools that check RPM. You bike, if the fuel screw is perfect, can idle as slowas 800 rpm, which is painfully slow, your bike would be bouncing at that speed. Set it fast, then adust it just a tad less than fast.

I know this is tough to know when you have nothing to go by. If you have a reasonably decent dealer, they can pop the shop tack on and let you get a idea what the speed is and what it sounds like.

+1 Good idea. FYI Stock engine can tolerate the usual 1,500 rpm idle. Modified engines like 1650+ at a slight sacrifice in off idle vacuum. But nobody rides down that low anyway.

[yyzmxs]

Is this the Vapor mentioned above?

http://www.trailtech.net/75-301.html

[Chas_M]

Retards timing slightly for emissions reasons

I have seen this 'Old Wives Tale' repeatedly bandied about. It is not true. The primary function of the TPS in the FCR carb is to increase the default CDI advance curve during part throttle operation. The added advance diminishes as the throttle is opened. At full throttle the advance curve reverts to the default advance curve built in to the CDI. The TPS (theoretically) increases part throttle fuel economy and keeps full throttle detonation potential to a minimum.

[William1]

You are incorrect. A TPS on ANY CARB solely provides a signal to the CDI. CDI's all handle it differently.

What I stated is the case with a DRZ. A DRZ with the TPS disconnected defaults to the advance map, which the TPS would enable about 2,000 RPM.

With most other CDI's it causes the CDI (in concert with the RPM signal) to switch between two or more ignition maps. Most other CDI's default to a retard map with the TPS unplugged, the opposite of a DRZ. None of this has anything to do with a FCR. In fact, most that install a FCR on a DRZ do not get them with TPS as it is so unneeded.

[William1]

Who has removed the TPS completely from their carb?

If your carb has a TPS on it, leave it on, but you can unplug it. Removing it and not having a cover provides a entry point for grit.

[William1]

+1 Good idea. FYI Stock engine can tolerate the usual 1,500 rpm idle. Modified engines like 1650+ at a slight sacrifice in off idle vacuum. But nobody rides down that low anyway.

I tend to set idles on the high side. My DRZ stock and the 470 both have idles set to 1,800 to 1,900. I find the engine is a bit quieter (less 'rattly'), I never get that 'nail the throttle single piston slap' and it greatly reduces any propensity for a bog.

[eddie odell]

You are incorrect. A TPS on ANY CARB solely provides a signal to the CDI. CDI's all handle it differently.

What I stated is the case with a DRZ. A DRZ with the TPS disconnected defaults to the advance map, which the TPS would enable about 2,000 RPM.

With most other CDI's it causes the CDI (in concert with the RPM signal) to switch between two or more ignition maps. Most other CDI's default to a retard map with the TPS unplugged, the opposite of a DRZ. None of this has anything to do with a FCR. In fact, most that install a FCR on a DRZ do not get them with TPS as it is so unneeded.

Well done and well said. I'm glad you did it so I wouldn't have to.

[Wayward Son]

the best thing about TT is we get to relive the past non stop.