Well.. The car was sold in north america. It was in Florida when I purchased it.

 

and the year is?

 

1994, 3.9 The engine number is 56D31995B. I think that the engine is not the original because I purchased in ebay a water pump and when I tried to install it, realized that it was different.

 

it is definitely not a '94 exhaust...

The '94 - '95 Discovery only had two (upstream of cats) O2 sensors. If you have four then someone has possibly updated your engine, exhaust and ECM.

I have just had a nutty thought. Would whomever replaced your engine have replaced the ECM too??? It is possible to run the 4.0 engine with the '94 ECM (14CUX).... certain sensors would just not be used.

Are the rear / downstream O2's actually connected??? If they are and you can trace them back to the ECM then you are running the post '94 - '95 ECM which is GEMS. In that case... you're better off replacing the cats sometime soon. Do you know where the ECM is located on your rig? Engine bay or behind the glove box?

IF you are running the 14CUX ECM then feel free to cut those cats out.

 

Mine were off when I bought it and I had to put a cat back on to pass inspection, it is high flow and I didn't see any diff in mpg after the change. A good tune up will do more for you, and o2s. Higher octane gas will help, I don't know how they calculate octane in Guatemala but if it is like the UK, your 85 is more like 87 in the US.