Error Code on 98 Discovery

[DiscoveryUSA]

So I'm new to this and I have a 1998 Land Rover Discovery LSE that has been giving me a few problems. Last week it started to lose power when driving it. Then would lose power and then run fine for a minute and lose power again and would do this for about ten minutes then run fine. Not sure what the problem is but I got a code reader and the codes it gave me were:
P0300
Misfire On Multiple Cylinder
P0307
Misfire Cylinder 7
P0420
Catalyst Efficiency Low Fault Bank A
P1316
Misfire Excessive Emissions Fault
Does anyone know what could be causing the loss of power and then be fine? I have changed the plugs and wires as well as the coil packs with no luck. Any help would be great at this point......

[listerdiesel]

If it is fuel injection then check/replace the injector on No7 cylinder for a start.

If Carburettor then check for broken gasket(s) on the inlet manifold.

Peter

[DiscoveryUSA]

it is fuel injected so maybe I will try that.

[listerdiesel]

It's a bit of a game getting them out, depending on which injection system you have. The later Bosch Motronic system has the 'bunch of bananas' inlet manifold with the plenum chamber and throttle on the front, earlier units have the single rectangular airbox on top.

Bear in mind that the injection rail will have high pressure petrol inside, so be careful undoing the feed pipe.

The injectors just push into the inlet manifold with an O ring and washer. Make sure the washer comes out with the injector, and that there is not another washer already in the hole before you refit the injector.

Peter