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Discussion Starter · #1 ·
Investigating annoying surging at cruise speed for months on my TREK I discovered my TPS is sending erratic position feedback in cruise conditions. For example, jumping between 10% and 16% under constant throttle at 3,300 rpm. This would obviously cause erratic running due to the large fluctuations in fuel delivery at constant speed and air flow. A bit of investigation revealed the potentiometer style TPS with a carbon track and brass contact are prone to wear under use and vibration. A new TPS is on the way but I wonder if anyone has addressed this by fitting a non-contact (Hall Effect) TPS? I apologise if this has already been addressed in the forums but a quick search did not throw-up anything.
 

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I have just had the same thing with mine .. it was going through all the positions from 1% to 100% but skipped 5% every time .
So id already cleaned it with electrical cleaner ..no joy so I then undid the fixing screws and rotated it in a way to eliminate the bad bit then reset the TPS . It's been fine for my last few test rides .
A new one will be on the cards after my trip .
 

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.. I wonder if anyone has addressed this by fitting a non-contact (Hall Effect) TPS?
Not as far as i know.
The TPS is also a BMW part made by Dellorto. I've had success substituting one off a BMW, but others have not. It's a question of range. Some will not position low enough for the ECU to deal with.
I'm on my second, at 136,000 km, so it isn't a highly problematic part, but if you can come up with a more reliable device I'd be most interested.
 

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Discussion Starter · #4 · (Edited)
Not as far as i know.
The TPS is also a BMW part made by Dellorto. I've had success substituting one off a BMW, but others have not. It's a question of range. Some will not position low enough for the ECU to deal with.
I'm on my second, at 136,000 km, so it isn't a highly problematic part, but if you can come up with a more reliable device I'd be most interested.
Thanks for the info on your site Errol, which enabled me to identify supposedly equivalent units selling for a reasonable price. I have a LÖWE automobil®: 63591 ordered, which is offered as the correct replacement for the BMW unit specified in the notes on your site. My bike spends the major proportion of its operating time sitting at 95-100 km/hr, as I live in rural SA where most of the roads are pretty flat & straight with 100 km/hr limits (and I value my license). The TPS seems to have gone erratic at the spot where it sits at 95-100 km/hr. I first became aware of the problem at about 25,000 km as far as I recall. It has now done 44,000 km. The TPS gives smooth behaviour when the bike is not running. I did not know I had an erratic TPS signal until I was riding with a tablet on the tank, monitoring TuneECU at 95 km/hr. I was trying to understand the annoying hesitation I feel at that speed, especially on rough roads. I noticed the TPS value was jumping around at constant throttle. Another member of the Aussie Benelli Riders Facebook group reported frustrations with erratic running in cruise at around 3500 rpm, despite replacing the TPS and a dyno tune, so I went in search of alternatives to the potentiometer. A search threw-up the Variohm Contactless TPS. https://www.efihardware.com/products/2821/Contactless-Throttle-Position-Sensor-Variohm It is listed at $264 but offered on eBay for as low as $208. It would require a bit of wiring to fit. In discussion on the Facebook page I noted: "It needs an output characteristic close enough to the original that the calibration process will deal with any difference. I think the essential electrical characteristics are: 1/. Three wires for: ground, a 5V reference voltage and an output. 2/. A linear output from about 0.9V to about 4.1V from throttle closed to fully open. According to the blurb on the website the Variohm unit shown is intended to replace "European" units. I think the Benelli unit fits that description. The advertised output of the Variohm is 1.2V at closed throttle to 4.2V at fully open. I hope the Walbro ECU will calibrate with these values." Errol from what you say the higher closed throttle value could make the Variohm unsuitable for the Benelli and I could be going down an unnecessary burrow anyhow. I have not fully investigated the physical aspects of installing the Variohm unit, although I think the shaft and screw centre dimensions are compatible. If the new potentiometer type TPS solves my problem I will not spend more time on the issue but if the erratic TPS signal continues or returns I will pursue the Variohm in the absence of a simpler or less expensive alternative.
 

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Could it be more of a problem if cruising mainly at one speed. With vibration and dust. What do they look like internally?
 

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Discussion Starter · #6 ·
Could it be more of a problem if cruising mainly at one speed. With vibration and dust. What do they look like internally?
You can see it here:
[video=youtube_share;2pHlk1pLsng]https://youtu.be/2pHlk1pLsng[/video]
Look from about 2:11 if you would rather not watch the disassembly. A screen shot is below.
TPS internals.jpg
 

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... Variohm Hall Effect TPS. .... It would require a bit of wiring to fit. .. characteristics are: 1/. Three wires for: ground, a 5V reference voltage and an output. 2/. A linear output from about 0.9V to about 4.1V from throttle closed to fully open..... The advertised output of the Variohm is 1.2V at closed throttle to 4.2V at fully open. I hope the Walbro ECU will calibrate with these values....
The two parts operate differently in that the OEM TPS is purely a variable resistor which requires 5V from the ECU to produce a voltage out proportional to angle.
The Hall TPS actually produces a voltage. There must be some amplification there because a Hall sensor doesn't produce that much by itself.
That said, if the Hall TPS can mimic the OEM TPS then I can't see why it wouldn't work, but it would have to be exactly the same. The ECU expects a particular V/degree rate, and only calibrates the closed position. The Hall TPS would have to be exactly the same rate.

Looking forward to your results, as the Hall part would have to be more reliable, providing the electronics is rock solid, given no mechanical degradation is possible. I'd switch to one next time mine fails - and it will.
 

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Discussion Starter · #8 · (Edited)
Variohm should work with Walbro. Maybe an issue with Sagem

I spoke to the Variohm man today and settled the concerns raised by Engenia plus some of my own.

The Variohm is designed to mimic the potentiometer/voltage splitter style TPS as a direct replacement. It is promoted to overcome problems with the potentiometer TPS that could not cope with the vibrations on race engines. I was told it has been successful on a VW Golf rally car where the engine vibration due to balance shaft removal repeatedly killed a Bosch pot TPS before the car could complete a race.

The Variohm can be wired for either anti-clockwise throttle opening or clockwise as required for the Benelli. The Bosch plug required can be supplied by www.efi.com along with the Variohm. See https://www.efihardware.com/products/2366/Bosch-3-Pin-Male-Junior-Timer-Connector

The TuneECU reset process for the Walbro ECU involves a full sweep. I trialled a reset on my old TPS with the idle screw set to give 1.2V. A sweep from 1.2V to full throttle at 4.14V then yielded a TPS range of 0% - 100%. This gives me confidence the TuneECU TPS reset on the Walbro ECU will work correctly with the Variohm. If the Sagem ECU TPS reset function on TuneECU still only sets the throttle closed voltage to zero % throttle opening the Variohm may not be suitable, because its minimum and maximum voltage output may be slightly higher than the original TPS.

The Benelli TPS mounting holes are oriented at 45 degrees to the flat on the throttle shaft. The Variohm body is attached to a plastic mounting flange with two screws. There are additional pairs of holes at different orientations in the mounting flange, enabling it to be oriented as required for the Benelli. See pic.
Variohm.jpg

The Benelli has an o-ring to seal between the TPS and the Dellorto throttle body. This appears to be to keep contaminants entering both the TPS and the throttle body. The Variohm is rated IP68, so I don't imagine it would need further sealing. I have not seen the Benelli throttle body dismantled so I don't know if there is a seal to stop contaminants entering between the throttle spindle and its bearing. If not, the Varohm would have to be sealed against the throttle body. This could probably be achieved with silicon sealant.

The final question is whether or not the Variohm will fit in the space available on the Benelli. It looks like it would but I guess that question will be finally settled if my replacement standard TPS lets me down again.
 

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Discussion Starter · #9 ·
Variohm is made in UK

The latest discovery, with help from Google, is the Variohm is made in the UK and is indeed a Hall Effect device despite what the Aussie sales bloke said. See https://www.variohm.com/images/datasheets/Euro_XP-Dshaft_1707_J.pdf

The blurb says the output is programmable. I assume the version sold by EFI Hardware of South Croydon, Victoria, Australia has been programmed to mimic the output of the European potentiometer TPS used on our Benelli triples. The advertised output is 1.2V at zero throttle to 4.2V at full throttle using a 5V reference voltage.
 

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The blurb says the output is programmable. I assume the version sold by EFI Hardware of South Croydon, Victoria, Australia has been programmed to mimic the output of the European potentiometer TPS used on our Benelli triples. The advertised output is 1.2V at zero throttle to 4.2V at full throttle using a 5V reference voltage.
If it is programmable then it should be possible to make it look exactly like the OEM part (ie. V/radian), in which case the Sagem ECU should be fine with just setting the close position.
All we need to know is the spec of the OEM part, and I could set up an experiment to measure that.

I just realised what this thing actually is. Honeywell, Allegro and NXP (to name a few) make the sensors themselves. It's based on a Hall device, and as we know they are sensitive to magnetic fields. A magnet is rotated in front of the sensor and the sensor responds with a voltage dependent on the field angle. All Variohm have done is packaged it with some electronics to tailor it to the TPS/ECU requirements.
Some time ago I was considering using one to determine the angle of a cord. The accelerometer currently doing the job was difficult to set up.

I'm liking this idea more and more :)
 

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Discussion Starter · #11 ·
Variohm Pricing

Best price I have found is about $213 including postage from T.I. Performance who apparently only deal and communicate on-line out of Victoria. https://www.tiperformance.com.au/pr...ess-8mm-d-shaft-throttle-position-sensor-tps/
The male 3 x 3.5mm Pin Bosch Junior Timer Connectors are $8.00 for five on Aliexpress. https://www.aliexpress.com/item/32781325168.html?spm=a2g0o.cart.0.0.71bd3c00fJkseu
Boots for the plug are $9 for five from the same store. https://www.aliexpress.com/item/330...28&spm=2114.12010615.8148356.1.2bed43d5GUx9x0
 

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Discussion Starter · #12 · (Edited)
TPS failed again - Variohm commissioned

The TPS on my TREK has failed again after 12 months and 8,500 km. The bike ran beautifully for the year but a fortnight ago it started to run rough and sometimes stall at small throttle openings, such as when I slowed for intersections. Data logging with TuneECU revealed the TPS % value was jumping around at about 7% throttle. That caused over-fuelling and the rough running. This time I fitted a Variohm Hall Effect TPS I purchased last year. I tried it last year but took it off again because it caused the bike to run lean. This time a 15% global increase to the fuel map fixed the problem. That is another story but essentially my whole map was too low but corrected by auto-adaption. In Winter the engine runs too cold for adaption, which only occurs over 80C coolant temperature, so the lean condition persisted until I adjusted the map. The charts attached show the slightly wobbly output of the old style TPS, the erratic TPS output at 7% throttle and the smooth output of the Variohm TPS. The pictures show the Variohm fitted. The logs show more work is required to fine tune the map but the bike is running sweetly again.
Log with Potentiometer TPS.jpg Erratic TPS static test.jpg Log with Variohm TPS.jpg IMG_20190902_125742.jpg IMG_20190902_215943.jpg Variohm TPS fitted.jpg
 

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Discussion Starter · #13 · (Edited)
TPS woes solved on TREK

I am very impressed with the Variohm Eurosensor XPD Throttle Position Sensor after a pretty good workout on my TREK yesterday. The ride was 370 km including everything from 40 km of smooth bitumen (where I gave it a fistful) to a few km of narrow, undulating kangaroo trail in damp sand with the occasional tree trunk to climb over and shrub to avoid in first gear. Most was on undulating, hard clay backroads covered in loose gravel, with some slow corners and intermediate gear work but mostly at 80-100 km/hr. The throttle was progressive and precise. The idle was much more consistent than it has been, although I can see from the TuneECU data logs that the stepper sometimes hangs-up causing a fast idle and lean condition until it is reset by switching off and on. The logs also show a bit more remapping was required. The fuel map is now looking more logical than before. Most obviously it had a low spot at small throttle opening where the old TPS eventually failed. It is pretty clear that I had been chasing the O2 feedback up by reducing the fuel to correct a rich spot caused by erratic TPS output. It seems to me the OEM TPS and Idle Air system have conspired to mar an otherwise excellent motorcycle. My idle air distributor bore and stepper plunger show scoring from contact where there should be none. I have a new stepper motor and await arrival of an idle air distributor from Maniac Motors to try and overcome that issue. However the new TPS has eliminated all the low speed crankiness. The engine now pulls cleanly from a slow idle to the redline and responds instantly to the slightest twist of the volume control. With no contact, no wear and no sensitivity to moisture, dust and vibration, this Hall Effect TPS is looking like the best $200 I have spent on the bike.
 

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What a fantastic detailed write up .
Very informative indeed .
looking forward to seeing how things progress with the new stepper motor parts when they arrive.

It's a real shame that we need to fix, modify and improve on a machine that could of been awesome from day one!

Rick
 

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Discussion Starter · #15 · (Edited)
Alternative TPS

VTP11 is another Variohm sensor that should be more durable than the original. It is marketed as being suitable for high vibration and heat environments in motorsport. In fact it looks to me very similar to the OEM device on my mates Triumph. It is less expensive than the XPD model (which is the Raceworks TPS-500 installed on my TREK) and it has a through shaft, so the space limitation on the TNT would not be a problem. This might be worth exploring for anyone with recurring TPS trouble.
See https://www.variohm.com/products/position-sensors/rotary-position-sensors/vtp11-throttle-sensor
and
https://www.compsystems.com.au/inde...riohm-vtp11-rotary-position-sensor-100-degree

On the other hand if you want the ultimate contactless TPS it is available here including the spacer it needs on the Benelli: https://www.efihardware.com/products/2821/Contactless-Throttle-Position-Sensor-Variohm
 

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Does this TPS fit in the TnT? Has anyone done it? I’m wanting to swap out the TPS in mine, ideally I’ll go with the Variohm, but if it won’t fit the TnT then I guess I’ll have to get a stock one instead.
 

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So I pulled the plug and fit the Variohm to the TnT1130.

I followed the process Redbaron described, rotating the sensor in its housing 45 degrees and reset the TPS with an Axone.

Currently the output value with throttle closed is 2.67 volts. So I’ll need to work out what’s going on with that.
36645
 

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I don’t know if yours might be the same but my bike has a different TPS fitted than what most people have and the shaft D is 180 degrees out.
 

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I don’t know if yours might be the same but my bike has a different TPS fitted than what most people have and the shaft D is 180 degrees out.
That’s actually somewhat reassuring.

mill be pulling the bike apart again on Saturday, so I’ll report back what I discover
 

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Here is the Variohm on my TnT1130.
TPS is oriented in the standard position in its housing (90°).

clocked as far anti-clockwise as possible. Volt reading is 0.7 - 4.1 Volts.
Resets fine with Tune ECU.

throttle response is far improved. No surging. Twitchiness is gone. Just nice, linear power through the rev range.

36660
36661
 
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