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Discussion Starter #1 (Edited)
2003 ZX6R (UK, European model), Akrapovic slip on, PCIII, stock airfilter, KLEEN air suction valves removed and blanked. Throttles balanced. No obvious air leaks. No FI errors.

The bike idles fine. It runs fine with clean fuelling throughout the rev range. But there's one exception. With the throttle just cracked open and at around 7k rpm, it surges badly like the engine is alternately cutting out and firing 3 or 4 times a second. Above or below that rev range it's clean. Open the throttle a fraction more and it's clean. The problem is that it coincides and is worst when following traffic at 30-40 mph in second. It's pretty much impossible to ride smoothly. The riding solution is to ride in a gear or two too high so the revs are below the critical range. It feels like it's fuel and not the secondary butterflies because the main butterflies are constant and only just open off idle. It's really like the ECU is chopping back and forth between shut throttle 0% fuel and open throttle 5% fuel.

I haven't yet gone down the route of replacing items like spark plugs and fuel pumps because on anything above 10% throttle through to WTO it's really sweet and running fine and strong. I've still got all the bits to return the bike to stock but it's a bit of a pain. It did it before fitting the PCIII. It's no different after fitting it.

I've run out of things to check. Any ideas?
 

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Discussion Starter #3
The map is currently straight off the Dynojet website.
207-514 - European model Akropovic slip-on exhaust and stock or aftermarket air filter

But as I said, the fueling feels fine across the rev range and across throttle opening. It's only this very specific region, throttle just cracked, 6500 to 7500 rpm. And it's doing the same thing with or without the PCIII. Now perhaps it can be tuned out. But looking at the map in this region, 6750 to 8250, 0% to 5% throttle it's all zeros. And yes, the help of an expert would be lovely :) but they're hard to find now for 17 year old bikes.

The gist is I don't believe this is normal, meaning that something is wrong. The question is what is wrong? 10 years ago I had an almost identical one of these bikes that was completely stock and it didn't do this. It had the same sharp throttle response but it didn't have the horrible glitch just off a closed throttle where the bike can't decide between go and stop and keeps cycling between them.

1581440451731.png
 

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Hello and welcome!

Maybe the throttle position sensor?
 

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Discussion Starter #5
Maybe the throttle position sensor?
Hi! The one you're not allowed to touch or adjust? And primary or secondary?

Quite a lot of the diagnostics in the workshop manual involve measuring voltages across pins on the plugs into the ECU. With Special Tool - Needle Adapter Set. I'm finding this quite difficult without the special tool.
 

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sometimes gotta bite the bullet and buy special stuff. A Ducati owner, comes with the territory.

In your case with the Power Commander, I'd suggest to contact their customer service and report your difficulties...go right to the source. Perhaps speaking with a tech there can guide you.
 

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Discussion Starter #7 (Edited)
Managed to get stable voltage readings at the ECU using bit of solid core wire pushed in next to the wire being measured in the connector. So, some more data points.
  • Throttle sensors input 5.0v Spot on spec.
  • Main throttle sensor output. 0.78v -> 3.95v Spec says 1.02/1.06 -> 4.62
  • Secondary throttle sensor. 1.31v -> 4.70v Spec says 1.08->4.60
  • Main TPS resistance 5.5k. Spec is 4k->6k
Interesting. The secondary throttles cycle through the range on ignition on. So I think reading a bit high is not a problem. But the main sensor connected to the throttle grip reading low perhaps is a problem. The manual is full of warnings about "Do not remove or adjust the main throttle sensor [A] since it has been adjusted and set with precision at the factory." In any case, it's a pain to get to as it's behind the frame rail and under the secondary stepper. I'm not sure it's possible to adjust it, even if you wanted to ignore the warnings.

Hmmm. What next?
 

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Discussion Starter #8 (Edited)
Yes! Result! I risked everything and adjusted the main TPS so it reads 1.02->4.35. Warm up the bike and set idle to 1300rpm. Get the digital multimeter set up, undo and lift the throttle bodies just enough to get at the TPS. Put a dab of paint so I can get it back to where it was. Loosen the torx screw just enough so I can very gingerly lift the connector and rotate the TPS. The top moved maybe 2mm to get to 1.02v. Tighten down the torx screw and put the throttle bodies back in. Check the idle to fully open voltages again. Set the throttle position on the PCIII so it runs from 0-100% Check the idle again and the TPS output voltage. Put everything back together and went for a ride. The glitch is gone. It's still a bit abrupt just off a closed throttle the way I remember the stock bike was. But once it's pulling, it's strong, with a clean linear throttle. But mainly, the just cracked throttle at 7000 rpm no longer does the on again, off again, surge.

Hooray!
 

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Discussion Starter #10
The unanswered question is why the main TPS moved or went out of adjustment. The bike was second hand with 35k miles on the clock. It's now 40k. Most of the mods had been done when we got it. I wonder if the previous owner had tried to deal with the problem and made it worse, or just been unable to fix it. There again, maybe it's just got old. The bikes got rearsets and had sticky tyres so maybe just used for trackdays where cracked throttle at 7k rpm just wasn't a problem.
 
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