03 V11 runs like crap

[drewladams]

Have a 03 V11. Ran great all summer. Let it set for a month while I took the BMW to Montana and now it will not run between 2000-3000 RPM starts and idles. Runs good over 3500. Great wide open. Left cylinder pops and backfires, spits and sputters. Throttle bodies have been synced, TPS adjusted to spec, new plugs, fresh gas. No luck. Just the left cylinder runs poorly and backfires. When I unplug the TPS, the backfire goes away, but of course it will not run below 2000 RPM, but the left cylinder gremlin seems to go away. WTF? When I adjusted the TPS, the voltage seemed to increase in a smooth linear fashion as I rolled the throttle to W.O. Did not appear to jump around, or show any sign that it was not working. Any suggestions? If it is a bad TPS, why just the left side?

[docc]

Ah, the forensics begin . . . first thing's first:

 

You didn't mention valve adjustment (first thing);

 

Check for corrosion at the spark plug wire exiting the coil.

 

Check battery condition (static voltage, voltage at idle, voltage at rpm)

 

Then there is the ignition switch to consider. . .

[luhbo]

... When I unplug the TPS, the backfire goes away, but of course it will not run below 2000 RPM, but the left cylinder gremlin seems to go away. WTF? ...

 

WTF does that mean?

 

Hubert

[Baldini]

Bad Coil, HT lead or connection?

[drewladams]

Valves were adjusted-checked in the spring, but I will check them again. Bike only has 14,000 miles. I will swap spark plug wires and see what it does. But it pulls so strong above 3500 RPM all the way up to red line. Just unridable between 2000-3000

RPM. It nearly blows the left throtle body off backfiring into the airbox on that side. And it came on all at once...

[Admin Jaap]

Also check the rubber tubing between throttle bodies and cylinders for cracks. They have a tendency to dry and crack. Also check under the clamps.

[mznyc]

Yup this sounds like a classic air leak.

Bike runs fine,then all of a sudden symptoms your describing .usually the rubber at the inlets but could also be header and mid pipe joints ,so check them all.

Cracks don't need to be big,just enough to change FI and that aint much.If no cracks,and all joints solid I would definitely check all other suggestions as they all make sense.Particularly the coils.

[luhbo]

... When I unplug the TPS, the backfire goes away, but of course it will not run below 2000 RPM, but the left cylinder gremlin seems to go away. WTF? ...

 

Again, what do you mean with '...when I unplug the TPS, the backfire goes away...'?

[Cliff]

I would try running some injector cleaner in a tank.

[Bob Hartman]

I'm in the air leak camp. They can be hard to find; might not present themselves until pressure changes at higher rpm. The usual test is to spray WD-40 or starter fluid around the inlet rubber bits at idle and listen for any change in engine speed. In your case you might want to remove clamps, as mentioned, and even have a look inside the rubbers. At the least, it's a free and easy way to eliminate one source of bother.

 

Exhaust system leaks can cause backfiring as well. Are all the joints snugged up/any black around them?

 

I'm aware of Ducati owners with the same sort of ECU find it was the brain at fault but if it's electrical I'd suspect a coil might be breaking down.

 

Bob

[helicopterjim R.I.P.]

Another possible air leak could be the the throttle butterfly shaft wearing the throttle body housing. This has happened to a friend of mine - left side - high miles. Open the throttle slightly whilst reaching down and put your finger on the bottom of the housing - directly onto the end of the shaft. You will probably be able to move it slightly if it is not worn but if it moves about 1/8th of an inch or approximately 6 mm as my friends does than you likely have an intake leak there.

[drewladams]

Battery voltage ok, spark plug lead resistance ok. Re checked the valves, and re adjusted the TPS. The intake boots look like brand new. Clamps are tight. No apparent intake leak. I will get the starting fluid out and see what I can make it do. Horrible backfiring in the left cylinder between 2000RPM and 3000RPM. When I pull the TPS electrical connecter, it will not run well below 3000RPM, but does not pop and backfire. When I adjust the TPS mV to over 600 mV at idle, it gets better but does not go away. Seems to move the stumble up the RPM range. So, it must be running very lean, and pulling the connector and increasing the mV to the TPS richens the mixture masking the lean condition. I will pull the intake boots and check the throttle body shafts. After that, it looks like I am going to put it on a trailer and take it to a dealer. I have never been so frustrated with a motorcycle. Like trying to ride a sneezing kangaroo.

[Tom M]

One more thing that you could try would be swapping the fuel injectors to see if the problem moves from the left cylinder to the right.

[drewladams]

The TPS at idle is now at 635 mV. The sneeze has moved up ro about 3200 RPM and is more manageable. The bike is now rideable but not as it should be. Going to pull the tank this weekend and replace all the fuel line inside the tank will replace the TPS with the Harley unit. Reset the throttle body sleeves, they are just fine. Cannot find an intake leak anywhere. The search continues.

[fotoguzzi]

what happens if you move the tps to lower voltage say 450mv? sounds like too much gas is being fed for the speed of the motor. are the air by pass screws open a half turn or so?