Ur quattro strange running

[Jim Haseltine]

Subject : 1984 Ur quattro, WR engine, MAC-01B ecu.

Under no-load condition the engine will rev without problem to 6000rpm
(probably higher but I didn't want to risk it).

When driving, the engine mis-fires at almost any revs between 1500 and 4000.
Will not rev beyond 4000.
Effect is varied, sometimes mis-firing at low revs and light throttle, other
times will mis-fire from 3000 revs at full throttle.
At times, when pulling away from a dead stop, engine won't pull and won't
take any revs and car 'creeps' like an automatic.
Switch off the ignition, restart immediatley and the car runs fine until the
revs and throttle reach a combination where it all starts again (usually
within yards), judders, misfires etc.

The mis-firing is very similar to the effect of a duff inlet manifold
temperature sensor, but at all sorts of revs.

Temperature sensor checks out ok, 22ohms.

Run other checks for RPM and firing sensors, coil/TCI/ECU connections, all
check out ok.

Discovered cables were transposed between Idle and WOT switches but moving
them back has no effect on the problem.

I'm not too happy with the thermo-pneumatic valve on the side of the head,
as the centre part of it (the black plastic with the two tubes) spins in the
fitting, not what I would expect.

Mixture and idle had been scr*wed with, to the effect that the engine would
run without the oil filler cap in place and would back-fire into the
manifold when cold.

Roughly reset mixture and idle and it doesn't back-fire any more.

As this only seems to happen with the engine under load, could this be a
symptom of a duff pressure transducer?

If anybody has any clues as to what could be the problem I'd be glad to read
them 'cos its driving me up the wall.


TIA

Jim Haseltine