throttle position sensor question

[mikesail]

Can someone describe how the throttle pot is mounted? it appears to be mounted on a stud, but I cannot tell what is the means to tighten or loosen. i do not recognize this fastening scheme.

Next can you tell me if there is any adjustment range for alignment, or is it fixed to one position?

[Byrdman]

Are you trying to tune the Power Commander?

[tomek]

The Big Book does not call for adjustment. I guess the system is self calibrating,basically once TP is bolted in ecu will figure out readings for closed and open throttle.

Closed would be 0.4-0.6 V

Open 4.2-4.8v

When openning and closing the throttle readings should smoothly increase/decrease.

[mikesail]

The Big Book does not call for adjustment. I guess the system is self calibrating,basically once TP is bolted in ecu will figure out readings for closed and open throttle.

Closed would be 0.4-0.6 V

Open 4.2-4.8v

When openning and closing the throttle readings should smoothly increase/decrease.

[/quote

I did check the pot a year ago, and it is fine.

Here is the reason for my interest. By measuring fuel pressure it is obvious that the vacuum is not maximum at closed throttle, vacuum increases at modest throttle opening. This means that the ECU cannot use the MAP sensor alone to figure mixture, especially at low throttle openings.

Therefore, I have to believe that it is delivering fuel based on throttle position, at least at these low throttle settings. Thus the throttle pot should have a direct effect on mixture for this operating region.

Tomek, I do not know how it could self calibrate without some training sequence. If you never go to full throttle then the ECU cannot know what that voltage is. Closed throttle is also not defined, with the choke holding the throttle partially open. I suspect that the ECU has fixed voltage values for throttle calibration, and that the pot is expected to deliver the exact setting, so any discrepency will cause a mixture error, at least for low throttle.

I did observe some sealing paint on the side of the pot, so it seems there may be a factory calibration. I just don't know how to move the fastener!

Jeff, I know that the usb PC can adjust for this, but I would like to understand the baseline operation and get it correct. The guy who did my PC said that my bike was extremely rich, I am hoping this might explain why.

[tomek]

You bring some valid points.

I believe EFI on XX is a typical dual stage system ,it is using MAP sensor for small throttle,and switches to TP everywhere else or combination of both.

System based on TP is not confused be pressure pulsation,or back flow in intake ( "double carburation") ports but does not have definition needed for those small throttle openings.Engine would have very poor On/OFF transition.That is why we have a hybrid here.

Calibration.

I guess you could use MAP readings to calibrate TP,let`s say at given rpms and MAP vacum TP reads X,ECU can compare that with stored data,and calibrate .

It has to have some self calibration ability,you know 0.4 to 0.6 volts,it is 50 % gain,,,,,,,,,,

Interestingly enough BIG Book does not call for any start up procedure for new TP,so I`m assuming it is selfcalibrating.

In case of, let`s say RX7 Turbo,car I know very well,you have to follow certain procedure after TP replacement.After that it self calibrates and adjust for wear.

[mikesail]

I suspect that a car will have different calibration needs because of emissions. It is possible that a bike does not need such fine tuning. I am curious about the idea that it uses MAP for part throttle, since I have observed that the vacuum power relationship is inverted at low throttle opening. I'm sure you know how carburators are flow sensing on the power circuits, but vacuum sensing for the idle circuit. I would think that using TP to set fuel in the low power region would be more reliable, by basically emulating a hilborn type of system. Any way to find out what our ECU really does? Of course for anyone who has seen an early 80's California Honda car emissions setup, nothing the japanese do here would seem crazy.

What you mention about setting the initial position of the RX7 pot makes sense to me, although I have a hard time believing it compensates for wear and aging. A good wirewound pot is extremely accurate, and has neglible aging. I think any attempt for a ECU to self calibrate would involve other sensors which are less accurate than the TP.

I think you make a mistake by saying the 400 to 600 mV closed setting gives a 50 percent gain change. It could be mostly offset instead of gain, it really depends on how the system defines its zero point and what the slope is of the measured quantity. I have never seen a flow chart of an ECU computation, so I really don't know what the computations are.

Is it believeable that the Bird has a fixed factory cal which is deemed close enough? That it is set as part of the TB assembly, and not intended to be touched again. And that the voltage range they give is really just to make sure nothing is broken, and not representative of what accuracy the ECU expects?

And finally, since no one has replied to this point, how do I loosen the pot mounting???

[tomek]

Well,TP in RX7 is not directly mounted on the shaft,there is cam,and push rod deal,so there is mechanical wear involved.

Older models of RX7 did not have self calibrating future and FSM calls for periodic adj.On newer as long TP is good there is no need to touch it.They do go bad.

Honestly I˛m not TP specialist,just trying to come to some logical conclusion.

As far as a part throttle deal,engine wear,valve lash,etc will effect vacum reading.Honestly,I don˛t see how engine would operate properly over its life if relied on TP alone.

Plus ,intake charge is not weightless,it takes some to accelerate when you open the throttle.

I understand pure car competition motors dont bother with Map sensor,but bikes need more gentle on-off transistion and definiton of TP is not good enough in first couple deg of throttle,,,,,,,,,,,

Why are you trying to mass with TP,,,,,,,,,,,,,I would, I guess, attack BARO or intake temperature sensors if I were trying to get across the line leaner or richer mixture.That is pretty much how PC2 works.

PC3 modulates lenght of injector pulse.

[mikesail]

OK, I have gotten to the throttle sensor finally. It is mounted with a tamper proof screw, whose head breaks off after it is torqued down. A little work with a dremel grinding disc to slot the head and the screw is easily removed. It is a 5mm screw, about 12 mm long. The pot has a metal insert around the screw hole to absorb the clamping force and not break the plastic body.

I will say that the pot calibration is very sensitive, moving it a few degrees caused the bike to stall when at idle. Since the Bird cruises at a very low throttle opening, I have to believe that this will greatly affect highway cruise operation. I'm just going to play with the setting for a few days, try to see where it is happy and what effect it has.

more later......

[cbrxxquad]

I cant read all this, right now, so this might be well, wrong, I have found after I put the mr turbo fuel regulator on, that the lower throttle settings allowed,,,,,,Idle settings,,,,, 750 rpm,,,,, have an effect. It the fi,,, might recalibrate tp settings.

On autos I have found that I can get better tune at the lowest rpm idle. The fi might also. I think it does.