Why is my Jaguar S-Type losing power?

My 2004 Jaguar S-Type has had a diagnostic test, which has resulted in a list of problems. It all started with a loss of power when driving up hill. I've been told I need two new cats, plus four Lambdas, a new set of plugs and ignition coils.

The cause I'm told, is the result of engine backfire. I have bought all the parts required, only to be told that it could just be air loss via one of the many pipes attached to the engine.

My question is, would the engine still run if the cats etc, are damaged and, would the engine tick over be erratic? I'm asking because it starts first time and idles without deviation and is not blowing loads of fumes from the exhaust.

Asked on 19 April 2015 by bojag.sjr

Answered by Honest John
If the catalytic converter matrixes are broken up you would notice a lack of power ascending hills and on the motorway because the engine could not exhale properly through the partially blocked cats. An exhaust emissions test would also determine how bad the situation was.
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