Surging ...It might be your Throttle Position Sensor is Bad

[Bixxer Bob]

One of the most annoying problems going right back to when I first got my Girly has been a slightly surging, snatchy throttle under 3,000 revs.  Sometimes it's worse than others, and every time I tried something I fooled myself that I'd fettled it only to find after a long run that I hadn't really.

Bit by bit I've worked my way through everything: throttle body air leaks, IACV air leaks, IACV checks, exhaust leaks (I know - that's popping and banging but I had that too) fuel maps, spare ECU, air temp sensor, air pressure sensor pipe, the works.

So today I changed the throttle position sensor and,,,,,

RESULT!!!

I really have fixed it this time!  Two clues back up the excellent ride I had this afternoon with the throttle behaving just as I would expect it too - even picking up smoothly out of corners.

First clue was immediately after I changed it, the Tuneboy fuel map that shows the throttle calculation in use was rock steady whereas it used to jump about a bit.

Second clue came when I put the old sensor on a scope.  There were a few spikes in the low throttle range.

So, theorising for a minute, if this sensor was the volume control on an old transistor radio it would crackle just as they used to do when the volume was adjusted when the pot got worn.  So I guess the ECU was seeing spikes instead of a steady voltage and was trying to adjust the fueling to match.

One for the knowledge base I think.  With Tuneboy it would be easy to diagnose if it happened again.  Otherwise, I'd be putting a scope on it while still on the bike.

[moose]

Hi Bixxer

That sounds exactly like my bike, and it is still doing it now.  I will certainly try this and hopefully it will sort mine out also.

I know I could the research myself but......seen as you've done it already  :D  could I be cheaky and ask for the part number and cost of this item, and if it is an off the shelf part or if it needs to be specially ordered.

Thanks.....an excited Rob  :D

[iansoady]

Very useful - filed for future reference, although the revised map has made mine absolutely smooth.

First clue was immediately after I changed it, the Tuneboy fuel map that shows the throttle calculation in use was rock steady whereas it used to jump about a bit.

Is this using A/F 1 when the engine's running?

[aesdj]

Cracking bit of info. Mine does that but its around 2250rpm and when your crawling in traffic etc. Its more noticeable in a certain gear. Is that what yours is, sorry WAS doing? Also mine pops in the overun but not all the time. I thought all bikes dids that especially high in the revs and are you some sort of NASA scientist or something. It takes me all my time to just to follow your e-mails :lol:

[akey]

nice one mate, glad you got it sorted, another one for the knowledge bank.

[Bixxer Bob]

...  could I be cheaky and ask for the part number and cost of this item, and if it is an off the shelf part or if it needs to be specially ordered.  :D

Dealer had to order it in, £35 but came the next day.  Don't forget, you need to order the throttle body gasket as well (I think that was about 69p) because you have to take the TBs off to get at it.   How to do the TBs is covered in my post here:

http://tigertriple.com/forum/viewtopic. ... tle+bodies (http://tigertriple.com/forum/index.php/topic,6777&highlight=throttle+bodies)

Only addition is unplug the sensor, remove the two torx screws holding it in place, fit the new one, replace the TBs.  Be careful with the torx screws they're threadlocked in and the heads are really soft.  Make sure the torx tool is a really good fit, Don't use cheap ones!!

I checked mine afterwards with the Tuneboy to see if the zero position needed re-setting but it was fine.  

Iansoady:  "Is this using A/F 1 when the engine's running? "  Yes, it only uses AF2 when you're on  100% engine load (which is not the same as 100% throttle, depending on revs and speed, 100% load can be from 30-40% throttle opening).

AESDJ: It was worst at very light throttle and engine loads at 2-3,000rpm. It was also snatchy when opening the throttle.  Now it's just, well.... normal - like all my other bikes have been.  It still pops on overrun a bit but no where near as bad as it used to be.  Checking the whole exhaust system for leaks to prevvent air being drawn in can help a lot.  I also found an easy way to do this: most non-franchise car dealers have a smoke device these days for checking leaks on turbo systems.  It's just as good at detecting leaks on exhausts.  They just put the smoke pipe and a bung into your can and watch for where the white smoke comes out.

[Bixxer Bob]

Got up this morning and thought "Is it really fixed this time?" so went for a ride.  


It is.


What a relief!!!

[EvilBetty]

I've got a scope (used it twice 15 years ago...) how did you measure the TPS?

Noticed mine is doing this.  Thought it went away when I balanced the TB's... apparently it didn't.

[iansoady]

Iansoady:  "Is this using A/F 1 when the engine's running? "  Yes, it only uses AF2 when you're on  100% engine load (which is not the same as 100% throttle, depending on revs and speed, 100% load can be from 30-40% throttle opening).

So presumably holding a fixed throttle opening, the highlighted box was jumping up & down the load axis? I assume you'd see it on the fuel map view as well as a varying TP.

[Bixxer Bob]

Iansoady:  "Is this using A/F 1 when the engine's running? "  Yes, it only uses AF2 when you're on  100% engine load (which is not the same as 100% throttle, depending on revs and speed, 100% load can be from 30-40% throttle opening).

So presumably holding a fixed throttle opening, the highlighted box was jumping up & down the load axis? I assume you'd see it on the fuel map view as well as a varying TP.

Not exactly.  It was on tickover, the TPS showing zero, but the AF1 map jumping about - anything up to three squares up and right of base.

EB.  Testing the TPS on the scope wasn't as straight forward as I thought it would be.  Putting 12v DC through it and monitoring the output didn't reveal anything - I naively thought (I'm mechanical not electrical remember) that by moving the TPS I'd see a simple voltage variation on the screen.  In the end I had to generate a signal, get the wave up on the screen and then watch for blips as I moved the TPS.

[EvilBetty]

I haven't messed with that thing since trade school.  Do I need a signal generator?  I don't think I've got one of those anymore (ever did)?

[Bixxer Bob]

Nah,  I used the output from an old battery charger.  Cheap ones are only half rectified.

[EvilBetty]

LOL you're going to have to draw this out for me so I don't electrocute myself :)

[EvilBetty]

Maybe I'm over thinking it but you may literally need to draw me a picture.   :oops:

[Bixxer Bob]

Nearly, I did it this way: