Yah well. I replaced the FPR as detailed in another thread and made sure that fuel pressure is now BMW's beloved 2.5 bar. Engine runs like a bag of rusty Irish nails and stalls below 2000 (!!) rpm. Petrol is urinating out of the exhaust/silencer joint. All four cylinders are firing. What I've done:

- Checked the thermostat (seemed to react okay when subjected to the various warm water temperatures) and then replaced it with one I knew was good
- Changed the temperature sensor relay
- Wiring loom is all good (I made it, but it doesn't mean that it was perfect from the start. It wasn't - but that's another story. At the time the bike ran reasonably well with just enough wiring harness to fire it up, so I completed the job)
- Injectors are putting out a good spray pattern. I cleaned them through with carb cleaner anyway
- Spark plugs are new with the correct gap, but I get the same problem with the old ones
- Crankcase breather has been replaced because it was showing signs of starting to split
- All other intake rubbers are okay - no signs of any splitting or perishing. They were replaced about ten years ago with spanky new ones secured with worm drives, so it's easy to get a look at them
- Disconnected the fuel pump while running and as the fuel runs out, the engine starts purring beautifully (as expected given the problem)
- Fuel filter has been replaced and inserted the right way round (this time)...
- Air filter is good and properly seated
- Swapped out both the ICU and FICU with no change in behaviour
- Also swapped out the airbox and MAF

LFB ran nicely for about fifteen miles on the way to the annual MoT test and then threw a sulk before I got there. Since then it's been over-fuelling like crazy; somefink somewear is telling it that the engine is cold. Anyone any ideas....?

Did you change the temp sensor itself?

Yes. No.1 on the list above.

Edit: guess it's not beyond the realms of possibility that the replacement isn't behaving. I'll do the heat test on that tomorrow. It's a good job that the radiator is only filled with plain water for now!

N° 2 is the temp sensor relay, not the temp sensor.

Edited. You were quick!

Maybe the return line is defective and kinked, or collapsing internally and raising fuel pressure at the rail.

Are the injectors pulsing or are they open all the time? 

If the fuel pressure regulator is adjustable, what happens if you reduce the pressure to where the engine runs well?

My K100 did that - gas flowing out of exhaust.

Problem: A previous owner or tech had put the temp sensor back on the pipe coming out of the head BUT they forgot the wire clip so the temp sensor eventually fell off. Seeing infinite resistance, the L-Jet thought that  the engine was at 0 degrees Kelvin and fed as much fuel as it could.

@Laitch: New lines all through and flowing in nice curves (oo - err!)
@Point-Seven-five: the engine used to run well (and did for a short while) so it's a 'new' fault and I don't want to mess with the FPR in case the fault decides to disappear at a most inconvenient time (but I will check the injectors tomorrow. They rattle like buggery when subjected to 50Hz (approx 3000rpm) but another check won't go amiss)
@duck: that clip is definately on there and the connector is welll secured

Can't hurt and is easy to check the temp sensor resistance at L-Jet pin 10.

Well, the fnbtch has fixed itself. I started off with the same problems as yesterday, then

- rechecked the temperature sensor
- put an older one back in
- no change in engine behaviour
- checked the wiring as per Duck's suggestion - all perfect
- switched the FICU for the one off Kostenlot - no change in behaviour again
- pulled the injectors and grinned as the cylinders launched fireworks in 4-2-3-1 order
- injectors were visibly pulsing and the pattern on the floor was nice and circular for each one
- reinserted the injectors and reconnected all hoses
- thumbed the start button to clear any remaining fuel in the hoses (hello? that sounded different)
- re-attached the tank and the damn thing immediately settled into a steady idle
I HATE IT WHEN A PROBLEM LIKE THAT FIXES ITSELF  

So what did I do that I hadn't done before? Checked the injectors. That's it; I haven't got a clue how that could fix an over-fuelling problem.

Pat the sleeping dog on the head.....gently.
And walk away.

"pulled the injectors and grinned as the cylinders launched fireworks in 4-2-3-1 order"

Your crank's broken. 


(Or are you just checking we're paying attention?)

Where did the temperature sensor come from? 

I have a similar issue on my RS and I am very curious as to cause. I know all the kit is good, changed temp sensor at one point [got a few brand new ones] and am a little suspicious of them. clips etc all good.

Olaf: The sensor that's now in there used to be in LFB, then got replaced because a while back I thought it might be buggered, then was put back in there yesterday.

Chris: Well that was the order the fireworks went off in!

If you used the old copper washer under the temp sensor be warned copper oxide will only pass current in one direction. I remember charlie chasing a problem all around the woods and when he cleaned the washer or a new one (don't remember which) it came good.
You may have rectified the problem by changing the temp sensor.

Both the old washer and the new one were/are aluminium. I'm not sure that was the problem Rick, because after I'd changed it the engine behaviour was still the same (overfuelling and pretending to be a bag of Irish nails).

That surely wasn't the cause and it's never a good feeling to know that the cause is likely to be lurking and waiting for your next ride.

It's worth repeating several problems with Chinese sourced CTS's. Sellers offering these often list the sensor they are selling as suitable for both 2 valve and 4 valve engines - (Impossible and misleading). Carefully look at the year/model compatibility they claim. If you have a sensor you suspect may be incorrect, do the temperature testing to check it performs to specification. A problem I had with a new Chinese CTS I fitted (then replaced) was that it distorted when being fitted. It was not over tightening it - just poor quality brass/manufacturing quality control). In discussions with Charlie, he recommends carefully tinning the copper washer with solder to resist corrosion which is a common cause of CTS malfunction. If you have to reuse a copper washer and don't have a new one available, consider annealing it to soften the copper and help with sealing. Noting the comparatively high price of the 2 valve BMW CTS, there are equivalent European made CTS's available of good quality and at less cost. Many other motorcycles and cars have similar problems of the CTS failing or malfunctioning - the CTS is not the most reliable electrical component.

@redrockmania: Good points. Fortunately in my case I was dealing with one OEM ('Bosch' stamped on the side) and one from Malpassi with good old 'Made in Italy' stamped on it. It's the Bosch one that's in there now.

@Rick G: don't tell me... I might think about trusting it when I've put another thousand or so miles on it.

another thing to 
Check is the wiring connector at the back left under the tank. 
Where the cable from the temp sensor joins the into the main loom and goes to the brain  

It was this connector that was giving Vic his problem as one of the wires had been ever so slightly pulled thus opening the connection within the connector block itself.  
any corrosion would also give the same result.