B11 stalls at idle

[Rafael]

Have an odd one here.

Just got done with a clutch job on my buddy's B11. Everything went well putting it together. Bike runs while driving. But stalls after its at idle for a minute or so. Also seems to be misfiring at start up.

Little history:
Was running great before the project was started.
The parts book incorrectly shows o-ring for timing sensor on top of shim. Upon start up it would not idle for more than 15 seconds. So after removing the timing sensor again I found a second shim with an o-ring under it.
Installed same shims and new o-ring with a dab of rtv.
Reset TPS and balanced the TBs and reset TPS again. Squirted some Sea Foam Deep creep into the stepper motor intake hose. Ran a VDSTS test on stepper motor, it said 'Complete' when it was done.
Seems to have improved but it still cuts out after a minute or so.
We thought that maybe the silicone is throwing off the sensor. So it came off again but this time there was no improvement in the idle. Oddly it seems to hunt around a little at idle a bit as if the sacred screw was turned but we didn't touch it. It seems like it misfires then shuts down. We kinda still suspect the timing sensor but not sure.

Any ideas for diagnostics?

Thanks in advance.

 

[kiwi dave]

Have you observed the action of the throttle on the TPS value using VDSTS? It sounds to me that the TPS might be playing up.

 

[john zibell]

The manual for the P8 ECU in downloads will tell you how to test the Cam position sensor. Spacing for that sensor is 0.7mm from the phenolic wheel. Also kiwi dave's suggestion is a good one as well.

 

[Rafael]

Have you observed the action of the throttle on the TPS value using VDSTS?

Yeah, think so. If by 'action' you mean twisting the throttle. Watched the TPS value roll up then back down, seemed to settle at a stable base value. But I'll hook it up again tomorrow.

Update: There were two shims originally, .8mm and .6mm. The .6 shim was a little warped so I went back in and took that one out. Now it starts up easier, instead of 3 misfires it starts right up. not sure if it starts as well as it did before. Runs well in the start up phase, then when the idle settles down it drops down to around 1000rpm then goes backup to about 1200 or so then drops again. But it no stall.

The manual for the P8 ECU in downloads will tell you how to test the Cam position sensor.

Thanks John. Figures the instructions are in a manual for an ECU other than the one on the bike. I'll check it out.

Edit: don't see P8 ECU manual the downloads section.

 

[john zibell]

The P8 was there. For some unknown reason I can't seem to upload the PDF. I'll send it to Todd to place in the downloads.

 

[john zibell]

Looked up the phase sensor value. It should have 680 ohms at 20 degrees C across the two contacts.

 

[PP-1753]

Sounds like a dirty stepper motor. You could also see if blocking off the hose to the stepper causes steady idle - if it does, the stepper is sticking.
However, it might also be the throttle bodies. Remove them and give them a clean in carb cleaner or similar. The spring mechanisms in mine were a bitch to clean - persist anyway. Carb cleaner down the hose from the airbox.

Let us know how you get on.

 

[john zibell]

Rafael, here is the manual I was talking about.

 

[Rafael]

thanks for the manual John.
My Buddy had located a procedure for setting the gap at the cam sensor. Basically, it says to use a washer on the end of the sensor to make contact with the cam then to use a feeler gauge to measure how much the sensor plate is lifted off the engine block. Then subtract the measured gap from the washer thickness to get the shimless gap. Then add the appropriate shim/s to reach a total gap of .6-.7mm. I don't see that procedure in the P8 Manual. It does give a gap spec of .6mm. But what does the +1.2mm mean? (0.6+1.2)

As it turns out, these measurements have to be done when the motor is out of the frame. I don't see how we can take a measurement now that the motor is in. We ran the bike with only the .8mm shim in and it ran fine but the idle would drop once in a while and cut out even less. Then when the new shims came in we added a .6 to the .8 to match what was there originally. Now it cuts out at idle pretty readily.

I don't think the cam sensor itself is the problem, because the bike runs great other than idle.
But we'll check the resistance and see if it's ok. TPS seems to work ok using the VDSTS. My buddy says it used to drop idle speed then go back up before this project. So, I'm wondering if it could be the stepper motor going out as Tony suspects. I did clean off the throttle plate with seafoam deep creep and cotton swabs. And we did spray some in the input tube to the stepper motor.

How much does the stepper motor do after the start up phase? If it helps keep the idle in spec range, then it may be stuck, but the start up phase goes ok. If the stepper motor is stuck open then idle mixture is too lean and the bike stalls? is this right? So to understand the stepper motor better it's just a solenoid that allow more air thru when the throttle plates are closed, right? Choke test on the stepper motor input hose next...

I thinking some dental molding material would work to do the gap measurement. I would hate to take the motor out just for this...

 

[kiwi dave]

I doubt it's the stepper motor causing your issues. I run my 1200 Sports with a pneumatic switch to remove the effects of the stepper motor to gain a lower idle and increased engine braking. The only negative effects of the stepper motor being disabled is an erratic idle on warm up.

You can easily remove the stepper motor out of the equation by temporarily pinching the rubber tube from the stepper motor. I'll bet your problem still exists.

 

[Rafael]

Dave you were sort of right. I pinched the stepper supply hose right after it came off the start up phase and the bike stalled. So, does that mean the stepper is stuck open? Seems like it should run better with the hose pinched. I pinched it again after the bike warmed up a bit and it took a little longer to stall.

 

[john zibell]

Air going into the intake track raises the idle speed. If the stepper isn't opening enough, then you will stall. To set the cam position sensor, I use a vernier caliper. Measure from the block to the phenolic wheel, and the cam position sensor length. The length of the cam position sensor needs to be 0.7mm less that the distance to the phenolic wheel. On Tonti bikes this is easy to do, nor sure about teh 1100 Breva. I would recommend going back to the shim that was in from the factory, then clean the line/stepper as described above. Easiest fix if it works. You have had several folks point you to the stepper, if you choose not to listen that is up to you.

 

[kiwi dave]

Is there any possibility that you have an air leak in your induct system? The stepper motor may be simply making it worse, i.e running too lean.

 

[PP-1753]

Ah, he says, the light came on! I had a similar problem and it was the rubber connectors between the throttle bodies and the inlet tracts. Make sure your hoses are all tightened up and that there is no cracks orother faults in the vacuum side of the inlet tract.

 

[Rafael]

Air going into the intake track raises the idle speed.

My understanding of the stepper motor is limited, I don't know if what you describe is just at start up or if the stepper regulates the idle throughout the operating temperature range.

The length of the cam position sensor needs to be 0.7mm less that the distance to the phenolic wheel.

I don't get it. There is no way to make the gap smaller only to make it bigger by adding shims. Found another manual that shows the air gap simply to be .5 to .7mm. But this factory manual totally leaves out any mention of shims in the procedure to determine the gap!

I would recommend going back to the shim that was in from the factory

We did, as I said in my post above, replace the shims we found in place with new shims of the same thickness. They are .8 and .6 together. It actually idles worse than with .8 alone.

You have had several folks point you to the stepper, if you choose not to listen that is up to you.

I always listen to GT members, especially you JZ! We did sqirt some SeaFoam Deep creep into the stepper input hose and ran the diagnostic of the VDSTS. Think I said that in my first post.

Kiwi Dave and Tony, that very thought crossed my mind yesterday. We'll be testing the intake boot for a leak next. We were trying to think of what might have changed during reassembly.

thanks for all the replies.

 

[Rafael]

Ok, post mortem here. LEARN from my mistake.

So, I tested the resistance the sensor and could not get a consistent reading, so we ordered a new one. Before I installed the new one, I measured the tips to compare them in order to make an adjustment to the shims. Well, I got a different measurement so I decided to take measurements at a spot 90 degree from my previous location. Low and behold got 2 different measurements on the old sensor. Took a closer look and the sensor plate was warped oh so slightly, so that the center is arched in the middle. This caused the sensor tip gap to increase. In my first post I had mentioned that the parts book shows the o-ring on top of the shim. I did not realize that there were 2 shims and that the o-ring was hiding under the second shim stuck on the block. So when we bolted the sensor on the plate was bent over the o-ring.

Took another resistance reading and got the spec reading, turns out it's just hard to get a reading with the pointy probes.

When installing the sensor with the motor in the frame, start with the pig tail oriented towards the top center of the motor then rotate it counterclockwise to avoid interference with the frame.