Running badly, on 3 cylinders

[cafcross]

Mate's 172 Cup is running horrible. The usual 3 cylinders, Scooby noise, loss of power etc. Fine when idling but when driving it goes all funny.

So far we've changed the leads, plugs, injectors, coil pack and lambda sensors and it's still doing it.

Any ideas?

 

[MicKPM]

Had it on diagnostics? Not looking for codes but looking at the live data... might also be worth scoping the injectors to.

Mick

 

[cafcross]

Yep, done diagnostics and showed no faults so a bit confused.

Sorry, but what do you mean by scoping the injectors?

 

[JackJack]

Oscilloscope.
http://www.picoauto.com/automotive-oscilloscope-guide/injectors.html

 

[sideways danny]

Compression test it