YZ426 TPS sensor

Shawn Mc · Jul 15, 2002

I want to advance the timing a couple of degrees, but not necessarily over the entire range. I was wondering if I advanced the TPS sensor making the computer think the throttle was open a little more than normal, if that would advance the timing in the lower RPM ranges. I usually run 100 octane unleaded fuel and the rest of the engine is stock so Im not worried about detonation. I know all the factory guys have the TPS removed, but I dont know where computer defaults to or how that would impact the mapping without being able to dump the 3D programing. Advancing the stator would advance the entire map. I dont want to do this. I dont want the thing getting lazy on the top end.

jescombe · Jul 16, 2002

Shawn,

I can't answer your question directly, but I once disconnected my TPS during a troubleshooting session on the dyno, and didn't see a significant change in performance anywhere. Possibly a slight loss of torque right off the bottom, but the way the throttle is opened tends to produce some variation there anyway. Would have needed more runs to be really sure. Anyhow, read into that what you will... :think:

Edit: It's worth pointing out that this was measuring full-throttle performance only, the TPS might have greater effect at smaller throttle openings.

I spent some time looking for an aftermarket ignition, but they all came out pretty expensive once you added in the programming facilities. I have good access to an eddy current dyno though, and think setting up an engine specific map may be worthwhile if I can find the right product...

HTH, Jon E.

Shawn Mc · Jul 16, 2002

Is it possible that they would use the TPS like an RPM sensitive advance? I would think that they would use the TPS to retard the timing at low RPM and higher throttle settings to avoid detonation. The loss in torque down low, could be from detonation on the bottom end, and could be cured with jetting, Ya think? Also, do you know what changes Yamaha made to the map from 2000-2001? I know they changed something I just dont know what. Im betting it was the low RPM timing settings.
Did you happen to check the timing of the engine without the TPS connected? Assuming the top end performance was unchanged, it can only be retarding the timing, Man im getting confused with too many scenarios. Id love to know how that thing (TPS) is used in the map.

Kramer · Jul 17, 2002

I can't tell you what you want to know, but I do know that the TPS cannot tell the ignition anything about rpm, only throttle opening.

The combination of throttle position and sensed RPM, though, implies load condition. So the ignition characteristics can be different at say 5k rpm wfo, vs, 5k rpm & 1/2 throttle.

Shawn Mc · Jul 17, 2002

Kramer, your right. And in that vein, advancing the TPS would screw me If im looking for low speed advance. Now if I retard the thing, making the ingition think the throttle is lower than normal, that should allow more advance at lower RPM, and throttle settings.

AS a side note, I hate not being able to adjust the timing. And 3D timing is a pain in the butt. Sure you can get away with crappy gas and high compression with 3D timing, but it still bugs me.

Shawn Mc · Jul 18, 2002

AS I contemplate the mod, Im thinking that possibly retarding the positioning would do what I want. If retarding the timing at lower RPM and larger throttle settings is the purpose of the TPS, it would reason that if the TPS is reading a lower throttle opening than what is set or expected by the computer, in relation to the RPM the computer wouldnt retard the timing to prevent detonation. Right?

jescombe · Jul 19, 2002

I'm only guessing here - but I suspect the CDI won't have a lot of throttle map points like an EFI system would. You might find there are only 3 or so curves that it moves between, and if that's the case you may need to tweak the pot by a larger angle than is physically possible to signigficantly influence the selection..

YZ426 TPS sensor

Shawn Mc

jescombe

Shawn Mc

Kramer

Shawn Mc

Shawn Mc

jescombe

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