TPS voltage offset with engine running

[raz]

How much difference do you guys experience measuring TPS voltage with engine on versus engine off?

 

As long as I've had my bike, the voltage with engine running is much higher. At first I didn't think much of it. Then I started to think it's wierd because even if the nominal 12V goes from 11.5V to 14V, the TPS is run from a stabilized 5V that should not vary much regardless of that.

 

Today I finally confirmed that, by establishing the fact that my TPS voltage is not affected at all if I connect a charger with engine off (voltage went from 12.6V to 13.5V, TPS output at idle remained at 414 ±3 mV).

 

When I start the engine though, TPS voltage immediately and consistently rises to 488 ±3 mV at idle. The problem is this causes the ECU to read one row too high, which is a Bad Thing™ at fully closed throttle, or idling at redlights. I could compensate for it, but if this is a problem with my particular bike, I better fix the real problem.

 

I'm thinking since the 5V is unaffected, it must be a grounding problem. The ECU ground sinks pretty high currents from the coils and injectors. But I have already improved the original grounding quite a lot, and I'm not sure where I should add more. So before I dig too much into this I wanted to know if this is pretty much normal. I know others have mentioned it, but do you have this much difference?

 

I am interested in V11 figures, but even more so in Sporti figures. And I'm particularly interested in MyECU figures

[Cliff]

I think it is due to the butterfly valve being sucked ( open in this case ) while the engine is running.

[dlaing]

Interesting posts.

I got a difference today of 521 and 582.

This could be a good reason to set the right set screw, to avoid flexing of the linkage at closed throttle.

This is a difference of 60mV at idle and perhaps more under hard deceleration.

Raz's difference is even greater.

[raz]

I think it is due to the butterfly valve being sucked ( open in this case ) while the engine is running.

That is an interesting theory, I should be able to verify that easily. If you're right I'm amazed it's so consistant and stable. I'll watch it under really hard decel too, it's should be worse then.

 

Interesting posts.

I got a difference today of 521 and 582.

This could be a good reason to set the right set screw, to avoid flexing of the linkage at closed throttle.

This is a difference of 60mV at idle and perhaps more under hard deceleration.

Raz's difference is even greater.

Thanks, that confirms my figures are not much worse than others. Maybe that supports Cliff's theory.

 

I've also studied the schematics and real world grounding. Even a severe grounding issue should not affect the 5V circuit much as long as it's not inside the ECU. And I'm pretty sure it's not.

 

I'll make some field studies!

[Cliff]

The idle screw would stop it closing but the problem is it openning.

[Cliff]

It probably due to wear in the cross linkage.

[luhbo]

To speak in MyEcu figures: 60 engine off - 56 engine running. I see no problem here. I think the plate gets sucked, on the other hand it then should be blown open when the engine pops. That's not the case either.

 

Why don't you just measure the 5V support to the TPS. As long as this is stable it's just a mechanical problem. Measure these 5V to the battery ground and then compare this to a measurement between 5V and ECU ground (cable at TPS), engine on and off both times. This should give you more correct answers.

 

Hubert

[dlaing]

The idle screw would stop it closing but the problem is it openning.

Thanks! So much for that idea.

[pasotibbs]

Thanks! So much for that idea.

Just to muddy the water even more, mine changes with temp !

I've got a MY15M so can monitor the TPS easily and as the bike warms up the TPS changes, (this could be due to the idle speed increasing as Cliff has said but I thought I'd mention it)

[Dan M]

Only a .02v difference with mine .536 - .538

 

The butterfly cannot be sucked open. What would happen when you closed the throttle at high rpm? If the shaft bushings are worn the butterfly can rock around some and alter readings. I wonder if the bikes with this variance are high milers.

[dlaing]

I wonder if the bikes with this variance are high milers.

Could be.

I thought I previously tested the difference and got about a 10mV variation.

But now at 43000 miles there is more difference.

[v11cafe]

http://www.v11lemans.com/forums/index.php?...mp;#entry145582

[raz]

I think it is due to the butterfly valve being sucked ( open in this case ) while the engine is running.

That does not seem to be the problem. In Optimiser figures, it's 85 with engine not running. It's consistently 100 with engine running, whether I do hard engine braking or just sit idling. With engine running, I tried backing off the linkage by hand at left or right side, and wiggle the butterfly shaft in other directions, but I only managed to lower it to 96 (some 20 mV decrease). The same is possible with engine off, with a similar amount.

 

So it doesn't seem to be mechanical. I'll check things with a multimeter when I get the time.

[Cliff]

It could be that the idle pressure is enough to take up the slack. That is why you don't see any more increase.

[raz]

It could be that the idle pressure is enough to take up the slack. That is why you don't see any more increase.

I thought I should be able to wiggle it down to 85 if that was it, but maybe you're right. Anyway, for the moment I should set TPS to the 100 seen with engine running, right? That ought to be more appropriate than the 85 only seen with engine off.