Throttle Position Sensor setting procedure for California and Bellagio

Written 07/13

Summary: TPS setting procedure with pictures for Cali and Bellagio, typified by the throttle cable coming into a central unit and a plastic link running out to each side.

The throttle bodies fitted to the California and Bellagio are unique to these two models.  They are 40mm bore and have a link from a central cable wheel out to each throttle blade.  So the procedure has a couple of variations from the other Guzzi models.  Generally the throttle bodies on other models have a cable wheel on one throttle, then a link from that to the other in a master/slave style relationship.  With the Cali and Bellagio throttle bodies it’s more two slaves (call it a co-op for the socialists among us) so the idle balance is not influenced by the running balance at all.

The throttle body set up procedure is the same for both the early P8 ecu and later 1.5M ecu bikes.  The photos relate to the later 1.5M ecu bikes with the small round TPS.  P8 ecu bikes generally have the large square TPS, but the concept and procedure are the same.

The photos below have red numbers to denote components and then yellow numbers and arrows to denote them being used later.  Each number is only used once.

All instructions are based on the premise that you have the equipment required up to and including the diagnostic tools and gas analyser.  You may not, and this will influence how far you can go.  Ideally you will go all the way.  It’s always nicer.

1/ Remove the crappy plastic throttle body covers.  They can have little cap screws or 5.5mm (from memory) hex screws as circled in yellow.

2/ The TPS is mounted under the LH throttle body.  The photo below shows the air bleed (1) and TPS (2).  The TPS screws are 7mm hex on earlier bikes or Torx20 on the later ones.  Getting all the yellow sealing paint out to allow the torx fitting to seat correctly can be a pain.

3/ On top of the LH throttle body is the blade arm pivot point for the black plastic arm coming from the central cable wheel (3) and the throttle balance adjuster screw (4).

4/ The throttle stop screw for the LH throttle body (9) is at the rear, as shown below.

5/ The RH throttle body is much the same, just mirrored.  Throttle blade arm pivot point for the black plastic arm coming from the central cable wheel (6), throttle stop screw at the rear (5), air bleed underneath (8).

5/ The screw at the central cable wheel is the fast idle adjustment.  It has nothing to do with throttle balance.  Although, given the little lever at the clutch side of the bars generally won’t stay where you put it, it often has very little to do with the fast idle speed either.

6/ Back probe the TPS connector to take the voltage across the two outer wires.  You need to turn the ignition on to power the circuit.  In its original position, you should see 400 – 500mV and up to 4.85V at full throttle.  I note the setting just for the sake of knowing.  If you don’t get the required voltage from the two outer wires you may need to try other combinations, but I believe that is correct.

7/ To baseline the TPS, disconnect the black plastic arm coming from the central cable wheel (3) by removing the little C clip.  Be careful, as these little clips are incredibly good at pissing off on you.  And spending half an hour crawling around the floor to find a 20c part is incredibly annoying.  Then wind out the throttle stop screw (9) until the throttle blade can fully close.  I tend to snap it shut to make sure it can fully shut, but then open and close it more gently to not get a false reading.  Gently closed with a little force is the best way to get a good base setting.  Generally you’d expect to see anywhere from 100 to 180mV.  Again, I note the setting just for the sake of knowing.

8/ Loosen the two TPS screws and move the TPS as required to give 150mV.  I always check the voltage again once the screws are tight, as things tend to move around enough to often frustrate you.

9/ Once you have 150mV with the throttle fully closed, wind the throttle stop screw (9) in again until you get the desired voltage for idle.  The manuals give the reading in degrees of throttle opening, which you read via the diagnostic software.  The spec is 3.2 to 3.6 degrees.  Nominally, this corresponds to 486 to 528mV.  The relationship is mV = (degrees x 105) + 150.  Although, the ecu doesn’t always read this the same.  No idea why.  You might set the throttle stop screw to, say, 486mV, but via the diagnostics you’ll get 2.9 degrees instead of 3.2.  Or 3.5.  Just the way it is.  I usually go by degrees, not mV.

In the past I have found variation between bikes from some needing the stop set to 3.2 degrees or they’ll idle too high to some set to 3.6 degrees and air bleeds wound out to bring the idle up.

From here in, the LH stop screw is not touched again.  Unless you have a too high idle condition after step 13 or 16.  Then you have to adjust as required to make it work, unfortunately.

10/ Reconnect the black plastic arm coming from the central cable wheel (3) and refit the c clip (just as easy to lose now as it was when removing).  Check to make sure the throttle hasn’t been opened at all by this.  The voltage out of the TPS will tell you if it has.  If the TPS voltage does change you need to add slack to the opening throttle cable or back off the fast idle adjusting screw (7) as required.

11/ Hook up the balance equipment to each manifold and wind the air bleeds (1) and (8) fully in.  I note how far out they were just for the sake of knowing.

12/ Remove the plugs in the headers and fit tubes to sample the idle mixture.  Didn’t take a photo of them, sorry.  Generally a 15mm hex head.

13/ Start and run the engine until warm.  It should idle to some extent with both air bleeds fully in (chuga chuga chuga).  Because the idle balance is not influenced by the running balance at all, you adjust the idle balance by the RH throttle stop screw (5) so that you have equal vacuum on both cylinders.

14/ Now you adjust the running balance.  This is a compromise based on how much variation you get in cylinder to cylinder vacuum as you open the throttle and increase the rpm above idle.  Also remember that you might get to 8 or so degrees opening at most when free revving it in neutral up to 6,000rpm or so, whereas on the road you’ll often be above that just cruising.  So you’re not getting a full “through the range” indication – there’s no way you’ll get to even quarter throttle on a free rev.  I just look at the variation in vacuum between the cylinders and adjust the balance screw (4) as required to give a best overall compromise.  If this adjustment changes the idle speed then you need to add slack to the opening throttle cable or back off the fast idle adjusting screw (7) as required.

15/ Next step is to set the idle speed.  Hopefully it’s not too high, so you wind out the air bleeds (1) and (8) as required to get the speed you want.  At this point open them to maintain equal vacuum on each cylinder.  There tends to be a strong temptation amongst many owners to idle them low, but ideally you want 1100rpm.  Don’t believe the tacho either, they tend to be wrong in either direction.

16/ Last step is to set the idle mixture.  On the P8 bikes this is done via the trimmer on the ecu.

The idle trimmer on them is the screw in a hole next to the large wiring loom connector often covered by a plastic cap. To access the trimmer you just dig the cap out.  See the photo below.

Of course, on the Cali with the P8, the trimmer is up under the pillion seat and although you can work the ecu down and out without pulling the pillion seat, it‘s as much of a pain in the arse as you’d expect.

The idle trimmer operates over a range of 4 turns, but it’s possible to turn past the end point in either direction endlessly without changing the trim pot output voltage. Duane Mitchell at Ultimap says you can set the trim pot to the default “central” position by turning the trim pot 5 turns clockwise and listening for a little click (it’s rather little). Then turn back 2 turns counter clockwise and this is the central position. You now have 2 turns in either direction for adjustment. I’m sure I’ve done it on my own bikes this way. Alternatively, you can remove the lid of the ECU (the top as it is fitted to the bike, mounting tabs to the bottom) and using a multimeter set the trimmer by its output voltage. See the diagram below for the location of the terminals to take the voltage from. This is the most accurate way to get the default “central” setting for those who like that sort of thing.

Just remember that you have 2 turns of adjustment in either direction – it may help to write down what you’ve done.

On the 1.5M ecu Cali (mounted behind the LH side cover) and the Bellagio with the 5.9M/5AM the trimmer is an electronic setting via the diagnostic tools.  Although, from 2003 onwards the Cali are closed loop, as is the Bellagio and generally there’s no idle mixture adjustment on these bikes.  The lambda sensor does that within its narrow band of adjustment.

Usually I aim for 4.5% CO idle mixture.  Given there is only one idle trimmer for both cylinders, I check the mixture and then adjust the trimmer to get the average between both cylinders where I want it. Then I adjust the air bleeds to give the same mixture in both headers. This means that the manifold vacuum balance or synchronisation at idle will often not be equal. That’s just how it is.  Equal mixture CO% is more important in my experience.

I do recall a P8 ecu Cali that would backfire if the mixture was leaner than 7%, so it is sometimes a compromise between theory and the practicality of best running or fuel economy, etc.  The above procedure assumes that at the end point the set up is as intended and the mapping is good and all will be well.  If the mapping is crap then it’s a bit of a crap shoot.

And if the idle is too high at this point with the air bleeds both wound fully in then you’re back to step 9 and 13, winding the throttle stop screws out as required to give the idle you need.

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