2008 Buell XB12Ss -- Die at idle

Are these throttle position sensor voltages a concern?

I get TPS low voltage/short to ground code.

Throttle closed -- 0.33V (varies from TPD 4 - 5%)
Throttle open -- 3.78V (TPD 85%)

All readings I took with Buelltooth. TPS reset has been done a few times.

Bike also dies at idle some times; idle slowly drops to 800-900rpm then dies. Guy I bought it from said 'it's a Buell thing'. I don't believe it is.

I have done voltage, continuity and resistance troubleshooting per the manuals. Everything wire and power wise up to the sensor checks out.

I will do a full on intro on the bike once I am not at work; but for now I just wanted to put that info out there.

I have read through searches on this forum.

I will be completing an IAC troubleshoot today; as well as checking for injector leak as per the manual, and the intake gasket leak.

At my local NAPA, the TPS4129 is 210$ CAD; cheaper off St. Paul's HD but it says that's for 1125 models. So unless I absolutely need to replace; I would like to get input.

Previous owner also did a big bore kit by boring out stock cases; paired with Jardine exhaust and Race ECU with a custom tune. Buelltooth measured AFV rear @ 75-80%. I tried resetting to 87% once to see if it made a difference, but it went back down. but for now, I just want to focus on mechanical parts and connections; not ECU tuning.

Is it also possible to have a failing O2 without it throwing a code?

Previous owner claims the bike dyno'd at 135hp and 130 torque.

as stated above, I will do an official intro to the bike and the concerns/help I am looking for. Apart from rotating the engine, I believe I am capable of doing most of the work.

Are these throttle position sensor voltages a concern?

yes. they are off a tad. more accurate to test via ohms. the values for the "orange dot" TPS are...as per Ray in OZ who is a genius with these things: That measures 4.08K ohms across the sensor.
Measuring from the sensor moving contact that measures 566 ohms at the butterfly fully closed position and goes up to 3.817 Kohms at fully open open.


2008-2010 XB and all 1125 TPS units the same. part # is buell P0279.5aa
best price around
https://www.ebay.com/p/Buell-1125-X.../1139727635?iid=143220686065&rt=nc&opts=opick

Is it also possible to have a failing O2 without it throwing a code?
yes....but extremely rare.


service the IAC assembly. i've written short simple write-up on here on how to perform same. typically doesn't fail or need to be replaced...but it is a good idea to service it.

redundant.....but....in all likelihood yet ANOTHER fuel pump requiring service/rebuild. cold start repeats....warm idle stalling....long crank-to-start episodes....lazy throttle response....back-firing thru TB....loss of power....all signs and symptoms of a failing pump.

Is there a way I can test the fuel pump without having to remove it? If its in the manual I can follow that, I just don't have access at work.

I have checked the resistance on the TPS but I didn't really know what values I was looking for at the moment so I will re-do tonight.

Thanks for the reply and the heads up on a possible fuel pump issue. I haven't noticed any back firing thru TB or having to repeatedly re-start the bike (if that's what you meant by cold start repeats). only once did I notice that the bike cranked over a little longer than usual, but it didn't have me worried at the time, and it may have been 1 or 2 extra cranks at most.

Here I am!:love_heart:
I only argue to "test before you guess", and I apply that to everything, especially expen$ive part$

lunaticfringe said:

i'm seeing them now fail on a daily basis

Click to expand...

Maybe you're right? Are you offering 100% refunds if you're wrong? I know Scrooge McLuniDuck is so rich that money doesn't matter, but us dirty plebs don't light our cigars with 100 dollar bills:angel:

lunaticfringe said:

other than simple diagnostics and checking its ground, i know nothing of ecm's or companion values.

Click to expand...

Obviously.:black_eyed: LOL. But let me help you.
The AFV value means the ECM is pulling about 25% of fuel out of the whole map for some reason. Even with a brand new fuel pump, the ECM will still pull out 25% of fuel out of the whole map... but the bike will be faster because your wallet is lighter from replacing a part that was good.

In Fact, if a pump was failing or clogged the AFV would be higher >100 because the ECM is trying to add fuel it can't get from a bad pump.

Mr. CocoaButterlover: You seem to have a grip on testing procedures and thats good. You may or may not have a problem with the TPS, and like Lunatic said the idle value is slightly low. I don't know if it's bad but fix the AFV issue first. Same goes for the IAC. Use Lunatics very helpful advise to remove and clean it (it's free):up:
The AFV should be at 95-105 with a good tune and stay there.
As a diagnostic step, use ECMDroid to re-set the AFV to 100 and in "ECM Parameters" set the minimum and maximum AFV values to 95-105 to narrow the adjustment the ECM can make, does the bike run better?

Theres still some fixing to do, but it's a good first step of diagnosis and it only costs you a little time. Seems like a win-win to me?

Is it just cleaning it with carb cleaner? I did take IAC out last week but it didn't seem ridiculously dirty in the port & sensor tip. I will clean anyhow. I also since put injector cleaner into the system just in case the injectors were leaking a bit. But I will test those out tonight with the bike on/off x 5 method in the manual tonight.

Cooter -- my problem is I don't know where to start with fixing the AFV issue. I will adjust parameters and try to take live screenshots before and after my ride from the Buelltooth screen. Although I won't be able to do that until tomorrow night. I'm hoping its not a leaky injector, but at the same time, if it was, it would be an easy fix. I'm hoping the tune is still good on the bike and it's not what needs adjusting.

I gotta get one anybody else ?

:upset: I also just realized that come the head gasket time. Since he bored out the original heads; there's going to be some issues there. Anybody have any suggestions for that? Unfortunately, that job I will likely have to take to a mechanic to rotate engine. The more my OCD kicks in the more I realize maybe I should've bought a stock XB12Ss. But then I realize the potentially this one could have when it's working well.

lunaticfringe said:

Are these throttle position sensor voltages a concern?

yes. they are off a tad. more accurate to test via ohms. the values for the "orange dot" TPS are...as per Ray in OZ who is a genius with these things: That measures 4.08K ohms across the sensor.
Measuring from the sensor moving contact that measures 566 ohms at the butterfly fully closed position and goes up to 3.817 Kohms at fully open open.


2008-2010 XB and all 1125 TPS units the same. part # is buell P0279.5aa
best price around
https://www.ebay.com/p/Buell-1125-X.../1139727635?iid=143220686065&rt=nc&opts=opick

Is it also possible to have a failing O2 without it throwing a code?
yes....but extremely rare.


service the IAC assembly. i've written short simple write-up on here on how to perform same. typically doesn't fail or need to be replaced...but it is a good idea to service it.

redundant.....but....in all likelihood yet ANOTHER fuel pump requiring service/rebuild. cold start repeats....warm idle stalling....long crank-to-start episodes....lazy throttle response....back-firing thru TB....loss of power....all signs and symptoms of a failing pump.

Click to expand...

Lots of information to take in. With no idea, But one thing I'm sure of is, almost all symptoms for failing pumps I'm experiencing. Warm idle stalling.. Lazy throttle response, loss of power, with lots of back firing thru TB. I had just changed the whole fuel assembly plus pump. There may be a chance that fixing was done wrong. Although I have run a test via the buelltooth but no errors at all. Is there a way to diagnose fuel pump without completely removing??. Let me add also, I bought the tps 4129

TPS VOLTAGE :: 4.08V at full throttle and 0.56V at closed throttle

At idle TPS voltage is 0.704 V (TPD 3.4)
At max throttle voltage is 4.575 V (TPD 85)
Its off of 2007 TPS.

Did you get anywhere on finding an intake leak?

samuelseggs said:

Let me add also, I bought the tps 4129

TPS VOLTAGE :: 4.08V at full throttle and 0.56V at closed throttle

Click to expand...

Were you getting similar readings to what I posted before replacing? Did it make any difference changing it?

Last night I didn't get to complete what I wanted, I ended up just buying material to clean the TB and IAC port. Tonight I will be checking the resistance, injectors to see if it leaks just following the manual procedure (simple), and then cleaning the IAC. If everything checks out, I will fire up the old girl and spray in some carb cleaner around the intakes, see how she reacts. I doubt simply cleaning my IAC will fix my issue but I can always hope. Judging by the voltages posted from Cossack, I may as well order up that dirty TPS sensor.

I have alligator clips for my multimeter with plastic covers on the end so I went on a search for ones without to no luck. I can't fit it into the TPS pins with the plastic ends so I'll likely burn them off tonight so that I can measure the ohms while twisting the throttle. Although at this point, I believe my TPS needs replacing.

Am I seeing this correctly. Is this the right TPS4129?

https://www.rockauto.com/en/moreinfo.php?pk=881722&cc=1352641&jsn=10

03-07 (DDFI2) TPS voltage can be tweaked simply by loosening the two bolts and rotating the TPS clockwise or counter... hence the need for a TPS reset as they will all show slightly different voltage. It is degrees that matter and that you can get a clean sweep from minimum (idle set screw stop) and maximum (85 degrees DDFI2). With software connected to the bike simply view degree value and verify the same value are achieved over and over by twisting the throttle grip. If it checks out OK you're just throwing money away.

lowkey said:

03-07 (DDFI2) TPS voltage can be tweaked simply by loosening the two bolts and rotating the TPS clockwise or counter... hence the need for a TPS reset as they will all show slightly different voltage. It is degrees that matter and that you can get a clean sweep from minimum (idle set screw stop) and maximum (85 degrees DDFI2). With software connected to the bike simply view degree value and verify the same value are achieved over and over by twisting the throttle grip. If it checks out OK you're just throwing money away.

Click to expand...

I have 2008.

I know... you and some others could use the info posted regardless. Stated HOW to verify TPS is working properly or not and why them posting their voltage is pointless... clean the IAC and verify it is working as intended.

Or buy new. https://st-paul-harley-davidson-buell.myshopify.com/products/p0282-5aa-genuine-buell-actuator-idle-air-control-iac-08-10-xb-1125r-cr-u9f

lowkey: You are totally right about DDFI-2, and I agree, posting voltages is pointless and confusing the issue. Cocoa means his TPS has no slots, no physical adjustment. DDFI-3. HTH you guys understand each other

Cocoa: I don't think your TPS values are causing any issue. A TPS re-set for DDFI-3 tells the ECM what the values are for idle and WOT instead of in DDFI-2 where you need to give the ECM the reading it expects*. Thats why it's non-adjustable in DDFI-3. And like lowkey said You still need a clean sweep test.

I am convinced the ECM taking 25% of fuel out of the bike for some reason is a big issue and yes, a leaky injector could cause the AFV to drop like yours is.

"As a diagnostic step, use ECMDroid to re-set the AFV to 100 and in "ECM Parameters" set the minimum and maximum AFV values to 95-105 to narrow the adjustment the ECM can make, does the bike run better?"

It's free, easy, and will answer a bunch of questions ^^^^


*over-simplify alert

Cooter said:

"As a diagnostic step, use ECMDroid to re-set the AFV to 100 and in "ECM Parameters" set the minimum and maximum AFV values to 95-105 to narrow the adjustment the ECM can make, does the bike run better?"

Click to expand...

You are a genius...
My AFV readings was 78.2 so I reset to 100 the Bike ran very well, but after a while the readings went back to 96.1

Does this mean I still have to check for a leakage at the TB??

cocoabutterlover said:

Am I seeing this correctly. Is this the right TPS4129?

https://www.rockauto.com/en/moreinfo.php?pk=881722&cc=1352641&jsn=10

Click to expand...

Whats your location... I have spare TPS you can have it.

cocoabutterlover said:

Were you getting similar readings to what I posted before replacing? Did it make any difference changing it?

Last night I didn't get to complete what I wanted, I ended up just buying material to clean the TB and IAC port. Tonight I will be checking the resistance, injectors to see if it leaks just following the manual procedure (simple), and then cleaning the IAC. If everything checks out, I will fire up the old girl and spray in some carb cleaner around the intakes, see how she reacts. I doubt simply cleaning my IAC will fix my issue but I can always hope. Judging by the voltages posted from Cossack, I may as well order up that dirty TPS sensor.

I have alligator clips for my multimeter with plastic covers on the end so I went on a search for ones without to no luck. I can't fit it into the TPS pins with the plastic ends so I'll likely burn them off tonight so that I can measure the ohms while twisting the throttle. Although at this point, I believe my TPS needs replacing.

Click to expand...

I really can't remember the readings.. Although according to the ecmdroid my tps was bad, so I swapped it out. Although TPS wasn't the only issue I had with my bike... I noticed a few changes though. Backfiring reduce and idles a bit much better... But i still had to deal with Grounds following LAF(Lunatic awesome fix) heheh