Fuel injected bike 3,000 rpm rough running

Hi all,

My gpz11 uni seems to be running roughly at around 3,000 rpm.

Up to 3k it runs perfectly and 4k and above it takes off like it should. Idles fine too. Plug colours all look pretty good.

cruising at 3k and it surges and hunts as though its running out of fuel. Just doesn’t feel crisp.

Do these bikes have a built-in step, in their fuel mapping to get through emmision testing?

Everything else checks out - new fuel pump, regulator, tank return valve, valve clearances just done and timing is spot on.

I don't know if it is possible to due with the space restrictions but in my car days we used to remove the injectors and fuel rail then sit the injectors in 4 glass jars and operate the fuel pump. You are looking for a nice clean break with finely atomised fuel. If there are any drips or dribbles then that injector isn't working correctly (for Bosch injectors we had a machine to pump "white spirit" thru them. This removed any crystallised build up and usually recovered them back to correct operation) if you do them together you can also see if the delivery rate is the same for all 4

Sounds like an fuel pressure drop. 

Wookie58 - it had all 4 injectors serviced by a bosch service centre about 600kms ago, so they’re probably still flowing Ok. It picks up fine and really takes off.

Scirocco - wouldn’t fuel pressure drop affect higher revs as well though?

In top gear at 3,000 rpm its barely on quarter throttle. When you’re cruising along on a constant throttle it feels almost like your closing and opening the throttle just slightly Almost like its missfiring, but its not. Bit weird to explain. Anything above or below that is fine.

i’m thinkiing it might be something to do with the throttle position sensor - although the resistance checks out to the manual tests.

I was going to suggest you check the airflow meter, but it looks like the unitrak doesn't have one?  Maybe that was the earlier bikes?  I thought some of the KZ fuel injection system used a barn door airflow sensor.

Anyway, looking at the DFI diagram for the unitrak the only inputs shown are the air temp, engine temp, throttle position, and engine speed.  It's probably worth checking those other sensors, but the throttle position sensor seems like the only one that is likely to have a funky spot at a specific RPM.

The test notes do say "Readings should change smoothly as the throttle is turned."  

They also call out a special tool for checking the throttle sensor, 57001-1003.   I wonder what that thing does.  

Thanks DOHC, yes thats right, no air flow meter on the uni.

the other sensors check out as per spec. Also, usually you get a dfi warning light if one goes out.

There are some instructions for adjusting the TPS on the net but it seems a bit hit and miss

www.kzrider.com/forum/3-carburetor/40331...-my-gpz1100-dfi-long

www.kzrider.com/forum/3-carburetor/40652...ne-tps-on-gpz1100-b2

That first thread suggest these bikes came with a flat spot around 3000 RPM.  Folks talk about tuning it out by adding a resistor to the air temp sensor.

 

DOHC - thanks so much for those threads. What they discuss does seem very similar to my bikes condition.

Finally got some time this weekend to try adjusting the TPS.

was fairly easy to do - but holy s___ what a difference it made!

no hesitation or hunting at lower revs now, it just takes off from two and a half thousand in any gear like a banshee.

plus i was getting decal popping on the overrun - seems to have disappeared too.

Best 10 mins fiddling with the bike in a long while. Rides much much smoother now.