What's this?

[Spout]

What exactly goes on inside this black box? (Bosch part on inlet tract - ignore green arrows)
In the parts fiche it's referred to as "Switch". Not very helpfull.

Is there an electrical contact that monitors throttle position? And then regulates fuel supply somehow?

When my throttle is held steady (at any opening) I lose power (I'm guessing due to fuel shortage). To get things going again I have to either slightly open or close the throttle - it "feels" like an electrical contact is being remade.
As I say this only occurs on a held throttle position - whether at 30mph in town or pulling hard at 95mph on the motorway. Trait not really noticed on A roads as throttle position is always changing.
It does feel strange 'throttling off' to accelerate!

I'm wondering if the electrical contacts (if there are any?) in this box might be dirty. Would I bugger anything up taking it off to have a look? (OK wiv spanners, numpty wiv elastictrickery)
Can the unit be replaced easily? or does it involve electronical thingies?

I did think that the fuelling problem could be the dreaded surging, but doesn't that only occur on small throttle openings?
I've fitted new fuel filter, spark plugs, air filter, set tappets (twice) and balanced t bodies - all to no effect.
I've even tried taking out the plug in the fuse box - made it run richer but didn't cure things.
When the problem started it was intermittent and would run fine for hundreds of miles (suggesting an on/off fault rather than a setting?) but using higher grade petrols seemed to cure things (doesn't now though).

So, what's the part called? and could it be the source of my problem?

Cheers...........

 

[finglonga]

Is there an electrical contact that monitors throttle position? And then regulates fuel supply somehow?

Thats it.

 

[littleredrooster]

Throttle position sensor. Do a search on TPS and try to stay awake - there's lots of them!

 

[cookie]

some of the few i've looked at are set a bit low.

set to 380mv and they often run better. not got time to tell you how. do a search.

 

[ROJAZ]

Paul

Not an expert, but your TPS sensor has obviously been tampered with (blue paint) and looks miles out of adjustment (left side fully up and right fully down)

You may have knocked it when you fell over out on one of your rides

 

[finglonga]

Paul

Not an expert, but your TPS sensor has obviously been tampered with (blue paint) and looks miles out of adjustment (left side fully up and right fully down)

You may have knocked it when you fell over out on one of your rides

I believe that picture is off ADVRider, the thread on how to change the cam tensioners.

 

[Den]

Do a search for the 9 million threads on SURGING.
TPS is the same as mine, up one side, down the other. Never been touched.

 

[Spout]

Cheers for the replies.
Pic was from an Advrider thread (on cam chain tensioner replacement thread) so I doubt it's mine! But you could be right Mark!

So the 'black box' is the throttle position sensor, which can be adjusted to give different voltages which magically convert to different fuel supplies. I might not (personally) be able to do anything about mine (as I said - electrical numpty!) - but at least I now know what it does.
Which brings me to a few more questions:

Does the TPS work in steps (ranges of throttle position) or is it linear?
I only have to adjust my throttle slightly to regain fuel flow.

Does it measure off a physical connection? Like a resistor, eg fuel gauge in the petrol tank. Or non touching (magnetic?)
Could this connection get mucky and cause my symptoms?

Can I safely take it apart and what would I use to clean it?
I vaguely remember liberally spraying around the TPS with WD40, could I have 'gummed up' the internals?
I used to have a portable CD player with a volume control pretty much like my throttle - no sound until tweeked ever so slightly up or down. Lots of dust was causing that.

Are there any links to pics of the internals?

Could any bad contacts be diagnosed by someone who knows his way around a multimeter? Or do I need a more BMW specific brain?

Having read up some more on 'surging' I don't think this is what I have. Mine only 'dies' - never surges ahead.

Anyway, thanks again, I'm off to do further searches.

 

[Chris G]

Cheers for the replies.
Pic was from an Advrider thread (on cam chain tensioner replacement thread) so I doubt it's mine! But you could be right Mark!

So the 'black box' is the throttle position sensor, which can be adjusted to give different voltages which magically convert to different fuel supplies. I might not (personally) be able to do anything about mine (as I said - electrical numpty!) - but at least I now know what it does.
Which brings me to a few more questions:

Does the TPS work in steps (ranges of throttle position) or is it linear?
I only have to adjust my throttle slightly to regain fuel flow.

Does it measure off a physical connection? Like a resistor, eg fuel gauge in the petrol tank. Or non touching (magnetic?)
Could this connection get mucky and cause my symptoms?

Can I safely take it apart and what would I use to clean it?
I vaguely remember liberally spraying around the TPS with WD40, could I have 'gummed up' the internals?
I used to have a portable CD player with a volume control pretty much like my throttle - no sound until tweeked ever so slightly up or down. Lots of dust was causing that.

Are there any links to pics of the internals?

Could any bad contacts be diagnosed by someone who knows his way around a multimeter? Or do I need a more BMW specific brain?

Having read up some more on 'surging' I don't think this is what I have. Mine only 'dies' - never surges ahead.

Anyway, thanks again, I'm off to do further searches.

hi Paul,

there is a bit of a problem with shaft that the throttle butterfly valves work on wearing prematurely, [I belive it's the bushes that the shaft runs in]

you may want to add that into the equation


see ya later

 

[Spout]

Cheers Chris for worrying me even more !

Happy update though:

I purchased myself a multimeter - in for a penny in for £16. Just how hard can checking the TPS voltage be?

So after 650 miles of bad running and lurching this weekend (didn't dare mess with the TPS before in case I buggered it up completely) I thought I'd have a go.

First thing to do was check the brown earth wire (always hoping for an easy cure) - it was fine with good continuity.

Then I raided the missus' sewing basket and inserted a pin in red and white wire connection. Turn ignition on and nothing. Jiggle pin about and reading of 348mV. Flick of the throttle sent the multimeter out of range but settled back to 349mV.

"Searching" on this site gave a preferable range of 370 to 400mV with 400 giving richer running. So I adjusted mine into that range at 370mV.
A few flicks of throttle had it resting between 369 and 371. Time for a test ride.

Well b*gger me! I wasn't expecting such a simple adjustment (less than a mm of turn on the TPS) to make such a difference. No low speed or high speed jerking at all.
Smooth power at all throttle openings and even at high speed there was non of that dieing every few hundred yards that had been making my motorway miles hell.
Vibration seemed to be down aswell, and a vacuum check confirmed balance.

Wish I'd done the adjustment before the weekend now

So it's smiles all round, and thanks for the replies.

 

[Spout]

After a longer test ride there's still an occassional slight hesitation. 95% there!

So I'll be trying Cookies recommendation and upping from 370mV to 380mV.

 

[MrIFan]

Just upped mine to 395 (on an 1100 though) and it's made a massive difference. much smoother and much better pick up from low revs. Possibly at the expense of a very slight increase in fuel consumption- not had time to check that yet.