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TPS reading survey

G

GrahamNZ

High Miler
Joined
Feb 17, 2009
Messages
618
Location
Wellington New Zealand
Given that the Guzzi specs say that with a closed throttle the TPS reading should be 4.7 degrees +/- 0.2 degrees, I wonder what reading we VDSTS users are tending to get?

In my case it's usually 4.5 degrees and sometimes 4.6
 
Same here 4.5 to 4.6 after reset. I have little experience, just recently got my VDST. Bike had drifted to 5.2 before the reset.

Wally
 
On both my Grisos I re-set the TPS at the first service and since then it NEVER changed.

Mind you I didn't stuff around with shit as the bike was running fine. No doubt if I'd done a whoel load of 'Tuning' to it I could of stuffed it up wonderfully! :)
 
Graham,

Most of the Brevas I've worked on come in at 4.6. However my personal bike began acting up a little for the reset and started to come in at 4.8 to 4.9. I then placed a .002 inch feeler gauge at the throttle stop, do the reset, and come out at 4.8 with the gauge between the throttle and the stop, and 4.6 degrees when I remove it.
 
I was told -and I don't know the reason or truth in it- That leaving the contact switch on with the engine off might cause the TPS to rise over time.

I always stop the bike with the key, so it never stays on without engine, and my TPS remains constant.
 
Zapa wrote:
I was told -and I don't know the reason or truth in it- That leaving the contact switch on with the engine off might cause the TPS to rise over time.

I always stop the bike with the key, so it never stays on without engine, and my TPS remains constant.
Click to expand...

I use the key to shut off the bike also therefore I do not believe this is related to my experience. What I've been experiencing is a function of the ECU reset. BTW, it does this with both VDSTS and AXONE. I just use the feeler gauge as a shim so that when it is removed, I get the reading I want at closed throttle.
 
I always stop my engine with the 'kill' switch, as the manual says, and then switch off the bike with the key at some point that is convenient to me. I have no reason to suspect that my TPS wanders all over the place.

In fact, the only time I had suspicions was just after my 20k service when I'd also gotten the stiffer rear shock that my mechanic installed from above. So I guess about everything got dis- and re-connected at that time.
For the 1st 100-200km, the bike ran rich. Much richer than usual, which felt nice, but made me lose at least 1l/100km in economy. It sorted itself, as if a good heavy hand on the throttle (after a highway toll station ;) ) made something "jump back". Never really understood what could have happened, but since mileage has been back to what it was before, I won't complain O:)
 
Interesting feedback, thanks.

During my recent "tuning orgy" the TPS started at 4.5 degrees and after adjusting one slightly loose tappet and balancing the vacuum a smidgeon, the TPS hovered between 4.5 and 4.6 degrees. All sweet I'm sure.

While I've never had the TPS off the Breva, I have removed the one on my Buell, where there's a tuning trick to position the sensor on its mounting screws to ensure that its plunger is very slightly preloaded before doing a reset. The TPS is just a spring-loaded pot and so is susceptable to wander if only from wear. While mine holds tune very well I'd not be surprised if the reading did move a bit at the 10,000km checking intervals. Also contributing to wander is any wear in the moving parts along the throttle link rod.

A pity that Guzzi didn't fit the TPS onto the factory-set left throttle body so that all adjusting the right body's vacuum would do it bring it into line with the left's. That's how it works on the latest Suzuki 650 V-twins.

To try to overcome the interference the stepper motor causes when adjusting the idling vacuum balance, I repeated that procedure immediately after a run when the idle vacuum was much steadier as the stepper motor seemed to be less active.
 
Once reset, mine stays at 4.6, but i do mess with the screw that shall not be touched, then reset the tps, pete started it, and I've gotten good improvment by experimentation. The sacred screw is not so sacred
 
Graham: I have kept a log. The first column is the initial reading and the 2nd column is after reset.


4.5 4.8
4.8 4.6
4.7 4.6
4.6 4.6
4.7 4.5
 
jon
Agreed that if you know what you're doing, adjusting the sacred screw isn't the end of the world. Just be certain that the vacuum balance is correct at 3,000rpm and at idle before touching the screw, be confident that the stepper motor is either working properly or is bypassed, and then use the screw carefully only to perfect the idling speed does seem to work OK. That has been proven to work.

NeroGuzzi
Nice one. Interesting first measurement - out of step with the rest. Tappets maybe?
 
GrahamNZ wrote:
NeroGuzzi
Nice one. Interesting first measurement - out of step with the rest. Tappets maybe?
Click to expand...

Yes. After witnessing a dealer molest my tappets, I took the bike home, reset tappets, and ordered the VDSTS from Todd. Below are the actual gaps I measured when I got home. They're going to make you cringe.

L/S intake initial gap: 0.20mm
L/S exhaust initial gap: 0.30mm
R/S intake initial gap: 0.25mm
R/S exhaust initial gap: 0.30mm

When the VDSTS arrived, I got the readings below.
Initial TPS: 4.5
Reset TPS: 4.8

Two weeks later (~300 miles), I checked TPS again and got the following:
Initial TPS: 4.8
Reset TPS: 4.6

All has been well since. Being self-sufficient is a wonderful thing! Thanks for posting the step-by-step instructions. It was very helpful.
 
NeroGuzzi

Yoicks! No wonder you're a do-it-yourselfer when faced with things like that.

Pleased to help where I can. Many people have helped me to get wiser over the years and trying to continue that theme seems a duty as much as a pleasure. :)
 
Why would mis-adjusted tappets have an effect on the TPS?

Or maybe that should read: If the ECU adapts its TPS zero-reference to mis-adjusted tappets, why does it not re-adapt it once the tappets have been re-adjusted?
(I guess no one actually tried if that's the case?)
 
RJVB

Poorly adjusted tappets won't alter the TPS setting, but when tappets are adjusted that alters the volumetric efficiency making a vacuum balance desirable. That in turn makes a TPS reset necessary.
 
Because a vacuum balance means touching one of the screws on the throttle bodies, altering air intake for a given throttle position? Yes, then I see it.

Kind of makes me wonder if there isn't another way to measure air intake, more in the way a carburetor does... but I guess that might not work very reliably, given the complexity of the underlying physics.
 
GrahamNZ said:
Given that the Guzzi specs say that with a closed throttle the TPS reading should be 4.7 degrees +/- 0.2 degrees, I wonder what reading we VDSTS users are tending to get?

In my case it's usually 4.5 degrees and sometimes 4.6
Click to expand...

My 1200 Sport consistently gets the same TPS readings you do.

Charlie
 
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