Questions to replacing obscure Lamba sensor.
 

The model is a '93 Jap spec WRX which is hesitating when under load at full chat.
So far I've changed the air flow meter, coil packs and fuel regulaor, but took it to a garage as it failed it's MOT on emissions showing a low Lamba reading, indicating that it's running to much fuel. They tested the Lamba sensor but couldn't get a reading from it.
So I need help tracking down down a new Lamba sensor. The probleem is that it's a 2 wire sensor on the downpipe protected by a metal cable surround, unlike most early imports which are 3 wire jobbie and live in the exhaust manifold.
They also said that of the 2 wires on the sensor, one of them was reading 5 volts with the engine runing. This is probably the supply wire (dunno if 5 volts is about right), but there was no reading on the other wire (I also presume that it's earthed via the exhaust).
I asked them if they could get a Bosch Lamba sensor to fit in place, but they wern't sure.

Help!!! I've got 3 weeks until the MOT runs out.

The sensor in the down pipe is the cat on fire sensor , the lambda sensor is in the manifold just below the up pipe

Yup, big bear is right. Ignore that little cat on fire sensor and attend to the lambda sensor in the headers.

If you are happy to cut and join wires then you can get a Bosch wire lambda sensor (0-0.9v) (about 30 to 40 quid)

Or a subaru one from a UK pre-97 car should be fine but expensive (200 ish quid!)

Api does the bosch one with wiring instructions for about 80 quid.

About the hesitation, have you changed the spark plugs??

No mate, but I guess by now that they are all sh1tted up.