This LRO reader emailed LRO.firstname.lastname@example.org looking for help with problematic fault codes and an accompanying metallic noise in his Discovery 2.
Since fitting a stainless steel free-flow exhaust to my LPG-converted Disco 2 V8, I’ve had these fault codes: P0420, P1173. I changed the coil packs and replaced all four lambda sensors and the HT leads with genuine parts and fitted NGK spark plugs.
My car runs rough on idle (with an accompanying metallic noise), otherwise it’s fine. I use 15/40 semi-synthetic oil – could this explain the noise? Might it be a vacuum leak? The exhaust is new right up to the manifolds, with new free-flow catalytic converters.
It’s a great vehicle that’s done only 65,000 miles. I wasconsidering a performance air filter and tune-up to make the most of the free-flow exhaust. Would this help?
Lewis Quebec, Welling, Kent
Fault code P0420 is: ‘Catalyst efficiency deteriorated left-handbank.’ P1173 is: ‘Downstream fuel trim malfunction bank 2.’ Put simply, this means thecatalytic converter on the left-hand side of the exhaust isn’t good enough to meet the parameters expected by the injection system. The only way around this is to contact the exhaust supplier and ask them to replace it.
Stainless steelexhaust systems do have a particular sound to them and this could well be the metallic noise you hear at tickover – assuming you’ve noticed it only since fitting the exhaust system. That being so, it’s perfectly normal and is nothing to worry about.
A performance air filter will help with the power very slightly but the best performance gain will be from tuning the injection parameters to suit the new parts fitted – basically an ECU rewrite.
The oil you’re using is listed as ‘Moderate climate alternative’ in the specifications so is correct for the engine and will be causing no problems.
This workshop advice appeared in the December 2015 issue of LRO. Back issues are available to download on digital devices here.