Breva 750 Cylinder Head Temp Sensor question

[Hugh Straub]

My 2006 Breva 750 stumbles and bucks in the 37-3900 rev range.  This surging happens regardless of whether the Lambda sensor is connected or not.  The bike stumbles regardless of which of the eight or so different ECU maps I use.  Plugs, wires and plug caps have been changed. Coils test OK.  I have two ECUs and the bucking happens with both.  Tappets carefully adjusted, butterflies balanced, until now, all sensors except cylinder head temperature checked and cleaned.

I have now pulled, checked and cleaned the injectors.  In the process, I was able to access the Cylinder Head Temperature sensor.   I pulled that sensor and checked its resistance at room temperature (on spec) as well as at 100 C (212 F) degrees.  The resistance specification at 100 C degrees is 220 ohms.  My sensor’s resistance at this temperature is 373 ohms.
 
Is the Cylinder Head temperature sensor the smoking gun?  Frankly, I’m running out of places to look. 

Many thanks & Kind regards

Hugh

[Guzzidad]

   If your temp sensor was bad it would run bad at all rpm's. Most likely the TPS. Throttle position sensor.

[guzzisteve]

 :1:

[Hugh Straub]

I have now checked the resistance on the TPS.   The Spec resistance reading between the A&B pins should be 1290 ohms. My reading is 1168 ohms.

The Spec resistance reading between the A&C pins should range between 1110 – 2400 ohms depending upon throttle setting.   My readings range between 1118 – 2110 ohms.
 
I was interested to see if I slightly cracked off from full throttle, my reading was slightly higher (2140 ohms) than at full throttle (2110).
I am not smart enough to know whether my TPS variations from spec are significant.  Good ideas most welcome.

Many thanks & Kind regards
Hugh

[Andy1]

My Breva 750 had a similar flat spot at around 4000rpm.  After getting a dealer to check it out (no improvement, they are all like that sir)  and getting frustrated with the problem when riding the bike around New Zealand, I finally sorted it out when we got the bike back to UK.  I sold it to the dealer.

Shame, in every other way it was a great bike, and I would have kept it.

The later single TB V7 engines are much better.

Andy1

[Muzz]

My Breva 750 has never had a flat spot. It may burp once or twice going from open loop to closed loop, but from then on it is just a wee turbine, smooth as. Pete Roper checked it out with his magic machine when he was out here and made a very slight tweak to compensate for an aging air cleaner, but everything was basically spot on and it has never been touched.

Of course, it is the fast RED colour, which does make a difference.

[Andy1]

Of course, that is it.  Mine was black......

But is n't a burp going from open loop to closed loop (actually from closed to open loop when accelerating) a sign of a flat spot?? Mine was also great at higher revs but around 60mph in top gave many a burp, some from the bike, some from me.

Andy1

[Kiwi_Roy]

Are you basing the resistance specs on this old document?
http://www.dpguzzi.com/efiman.pdf
Or do you have something more recent?

Your 373 Ohm reading would be equivalent to 80 degrees C, would it make much difference?
Having said that it seems to be a long way off.

You could get the bike hot and substitute a 220 Ohm fixed resistor (220 is a common value) or use a 1K potentiometer which would allow you to tune it for the best running.

[Muzz]

Of course, that is it.  Mine was black......

But is n't a burp going from open loop to closed loop (actually from closed to open loop when accelerating) a sign of a flat spot?? Mine was also great at higher revs but around 60mph in top gave many a burp, some from the bike, some from me.

Andy1

Mine relates to the temp. It was one of the things Pete checked (60deg was the magic number I think). Once it does its one or perhaps two burps, end of burping. Under normal conditions I suppose it is. To me a "flat spot" is simply an area where the donk does not respond as it should to a throttle setting. My "burp" is actually a slight stumble irrespective of throttle setting. At 60mph (4000rpm) she is absolutely getting ready to sing.

[Guzzidad]

      The fact that stumbling happens in the 37-3900 rev range pin points the TPS. My EV did the same thing in the 33-3500 rev range. That is the rev range most of your steady riding happens. The TPS is just a simple potentiometer and after many miles of being held in one place the contacts wear out. After a search I found a Harley TPS fit my bike at 1/3 the price of a Guzzi part.