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Erratic TPS causing surging

12K views 36 replies 7 participants last post by  samnu  
#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.
 
#28 ·
Don't expect too much from a Variohm. A new resistive TPS gave me stable readings and fine throttle control at low power, the same as the Variohm. The only problem was the resistive TPS eventually became erratic. The charts attached show the TPS signal before and after I replaced the TPS on a TreK1130, with only 10,000km on the display.

On the upper chart, the jagged green line is the signal from the original TPS. On the lower chart, the smooth green line is the signal from a new resistive Delphi TPS I fitted. That was only $75 delivered via eBay. Interestingly, the original TPS gave a smooth output in a static roll-on test, it only went that bit wobbly with the engine running. Engine vibration is likely to be a factor in the poor contact between the sliding contacts in the original TPS, while running. (The O2 feedback in the lower chart shows it is too rich, so I adjusted that later to reduce fuel consumption and avoid ECU adaption causing erratic behaviour.)

If you have problems with low-speed behaviour, the TPS signal is the first thing to check. It that is OK the problem might be the fuel map. If you have an O2 sensor fitted, the O2V signal will tell you if your fuelling is the problem.

When I bought my TreK it was very fussy at low revs and had very poor low speed torque. The intake and exhaust butterflies had been disabled, but it still had the stock fuel map. The O2V signal showed 1.15 at low speed, indicating a very lean condition. I adjusted the map to achieve feedback consistently between 0.95 and 1.00. That transformed the bike, making it purr like a kitten, with strong torque from idle. More recently, both my TNT899 and TNT1130 ran roughly at low speed. I did the same thing. I adjusted the maps to eliminate lean low speed running. Both now have civilised behaviour, with progressive throttle response. I also increased the fuel on deceleration to stop backfiring and give a smooth transition from deceleration to acceleration.
Image
 
#29 · (Edited)
Don't expect too much from a Variohm. A new resistive TPS gave me stable readings and fine throttle control at low power, the same as the Variohm. The only problem was the resistive TPS eventually became erratic. The charts attached show the TPS signal before and after I replaced the TPS on a TreK1130, with only 10,000km on the display.

On the upper chart, the jagged green line is the signal from the original TPS. On the lower chart, the smooth green line is the signal from a new resistive Delphi TPS I fitted. That was only $75 delivered via eBay. Interestingly, the original TPS gave a smooth output in a static roll-on test, it only went that bit wobbly with the engine running. Engine vibration is likely to be a factor in the poor contact between the sliding contacts in the original TPS, while running. (The O2 feedback in the lower chart shows it is too rich, so I adjusted that later to reduce fuel consumption and avoid ECU adaption causing erratic behaviour.)

If you have problems with low-speed behaviour, the TPS signal is the first thing to check. It that is OK the problem might be the fuel map. If you have an O2 sensor fitted, the O2V signal will tell you if your fuelling is the problem.

When I bought my TreK it was very fussy at low revs and had very poor low speed torque. The intake and exhaust butterflies had been disabled, but it still had the stock fuel map. The O2V signal showed 1.15 at low speed, indicating a very lean condition. I adjusted the map to achieve feedback consistently between 0.95 and 1.00. That transformed the bike, making it purr like a kitten, with strong torque from idle. More recently, both my TNT899 and TNT1130 ran roughly at low speed. I did the same thing. I adjusted the maps to eliminate lean low speed running. Both now have civilised behaviour, with progressive throttle response. I also increased the fuel on deceleration to stop backfiring and give a smooth transition from deceleration to acceleration.
View attachment 41958
Thanks! That is what I thought. I ordered that same delphi tps from autodoc for 19€. Practically for free.

other questions:
I guess yours had 02 fitted from factory because tune ecu reads it from ECU? Or did you fit it yourself?

Another question:
When I download map to tune ecu it frequently fails and I need to reprogram it from scratch with some CPR life support. I suspect fluctuating battery voltage. I have it on charger but its smart charger. Voltage drops from 12.5 to 11.9V static quite fast when all electronics are on. Then the voltage stays ar 11.9V. Lights all off, fuses taken off. Have you ever had problems? I think the tune ecu loses connection when the voltage drops below 12. But then when it reconnects the map write is succesfull because the voltage is static at 11.9-12V.
 
#26 · (Edited)
I have since fitted a Variohm to a TNT. There was no problem besides the awkward access. It just takes a little patience, plus a thin screwdriver to clear the Variohm housing. It might be easier if socket head screws are used with a ball ended Allen key. I just use Phillips head screws and a long, thin Phillips head screwdriver. The Variohm is only needed if you intend to keep the bike for a long time. In my experience, a new original style TPS is good for about 8,000km.
 
#27 ·
I have since fitted a Variohm to a TNT. There was no problem besides the awkward access. It just takes a little patience, plus a thin screwdriver to clear the Variohm housing. It might be easier if socket head screws are used with a ball ended Allen key. I just use Phillips head screws and a long, thin Phillips head screwdriver. The Variohm is only needed if you intend to keep the bike for a long time. In my experience, a new original style TPS is good for about 18,000km.
I plan on making it as robust as possible. I am also super interested as you wrote that it improved the running in the small rpm due to more stable readings. Have you still noticed these differences when you fitted it to TNT?
 
#22 ·
The vtp11 sensor is actually meant to be variohm version of jenvey tp11 sensor used in jenvey throttle body.

i might try the vtp11

 
#21 · (Edited)
Image

hi! Good research!

From the picture I see two wiring diagrams, So does this unit have 6 wires in total for both ways measuring? You just used the blue, green and yellow setup and covered the rest of the three with no use i guess? The blue green and yellow is for channel 2 and that was labeled as counterclockwise operation?
 
#20 ·
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
 
#17 ·
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
 
#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...tronics/sensors/rotary-position/variohm-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
 
#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.
 
#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.
 

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#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...oducts/variohm-eurosensor-contactless-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...item/33003927110.html?storeId=410028&spm=2114.12010615.8148356.1.2bed43d5GUx9x0
 
#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.
 
#10 · (Edited)
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 :)
 
#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.


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.
 
#3 ·
.. 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.
 
#4 · (Edited)
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.
 
#2 ·
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 .