UR Quattro flat spot

[Thebishop]

Hi just looking for a bit of help please my Ur Quattro WR seems to be having a issue under hard acceleration. Especially in the higher gears . It I accelerate hard initially it fine then struggles as if it's not getting enough fuel engine tone even changes and eventually it will build and go again. Just had a recent service including oil,filter, air filter and plugs. Any ideas pls.

[BackintheFold]

What revs does the problem happen at?

[Thebishop]

Sorry wasn't really looking at the rev but I think around 4000-5000 rev.

[BackintheFold]

Remove air flow sensor from front of air inlet. Clean CAREFULLY with carb cleaner and try again.
I think the sensors are NLA so is at your own risk.

[Thebishop]

Thanks will give that a go nxt wk. When I get a chance.

[Groundhog]

Unlikely to be the sensor itself but the wires attached to it. Unsolder them, strip the wires back a little and re-solder a-fresh.

[Thebishop]

Thanks will try this too my mechanic will be busy nxt wk.

[Groundhog]

If that doesn’t cure it it may be over boosting ( similar effect ) This can normally be seen as the boost gauge flashing/pulsing as the bar goes off the scale i.e boosting over 1.8 bar. This is generally the pipe between the exhaust manifold and wastegate blocking up.

[Thebishop]

Thanks for all the info and advice hopefully one of these will sort the issue

[Hanuman]

Flat spot and overboost...hmmm

I’m inclined to look at several connections, and the following functions

Inlet temp sensor.
As mentioned already, it needs a good connection. Some get them soldered. The original connections are welds, but the wire gauge is quite small, and therefore fragile as the wiring ages and becomes hardened. Another option is spade crimps- the size as used on speakers. But this can lead to a loose connection over time.

WOT switch and solenoid function.
There are two switches on the side of the throttle assembly. One is for the idle position. Tells the ECU it’s idling. The other controls the WOT solenoid. When you turn the ignition key to the first position, live but not running, you’ll hear the solenoid click. (Mounted on the firewall next to the hydraulic reservoir.)
If you open the throttle manually, as the micro switch is actuated, the solenoid should be triggered, also. This gives full throttle enrichment, or rather it just cancels the mixture control that exists at the lower throttle settings. The switches are just as exposed to environmental issues as various other electronics in The engine bay, they are 30+years old, and also unique. (Other micro switches have different mounting holes, so they cannot simply be swapped for something from RS/Farrell)
It’s not unknown for the WOT switch to become lazy, either not actuating correctly, or more commonly, it’s initially actuated, then as the throttle opens further the switch deactivates. This will cause leaning off of the mixture.
There’s a specification somewhere for the correct throttle angle at which the switch is actuated, and should remain so through the rest of the throttle opening.

Operation of the WOT, or rather getting the correct mixture, is also rather dependent upon the mixture being right in the first place. So make sure all those micro hoses are secure, leak free, and the mixture hasn’t been adjusted to compensate for any air leaks in the plumbing.