I`ve debated whether this fault and fix should be in the electrical section or here in the fuel section. Whilst the sensors are linked to the electronic system, they in fact control fueling.
I`ve had a continuous and tedious issue with fuelling which was noted at the last MOT. New sports cats had been fitted before the test and original pre and post cat Lambda sensors refitted, one above the cat on each downpipe and one after the cat on each exhaust pipe. The issue experienced at the MOT was one of high CO output at 1.9. Anything over 2.0 is an MOT fail. So it was a close run thing that my 350R gained its MOT certificate.
I`d eventualy ruled out a defective cat as both had been newly fitted just five months earlier. The problem had to lay elsewhere. Not long after the MOT I began to note engine check lights appearing on the dash. Intitially, no fault codes were present. It was difficult to deturmine was was wrong. A few thousand miles later, fault codes began to be itemisable. PO430 (Bank 2...near side rear sensor) would show up with the explanation that the nearside cat was "below threshold limits". PTJS1 helped me set up viewing occilloscopes for both rear sensors on my Android Torque Pro app and OBD11 ELM327 bluetooth unit which I have permanently plugged into the OBD socket in the car. This was most useful as the good offside post cat sensor reactions could be directly compared to that of the suspect near side post cat sensor. With the occilloscopes placed side by side on my Android phone, it was easy to see where the problem lay. The nearside Lambda would be a slow starter, would peak and trough badly and finally flat line along the bottom of the graph. My friendly Jagtech contact, Charlie Watkins took one look at the graph and condemned the near side post cat sensor on the spot.Here is a typical twin graph trace showing pretty evenly matched traces for the near side and off side sensors in good condition and now working well. Near side trace (new sensor) is on the left.
Lambda 02 sensors were an original Denso part on most modern Jaguars of the period. S-type, X350 and XF all appear to share the same parts. Two things are worth noting. Pre and post cat sensors are markedly different in size and price. The larger units are fitted before the cats and have a GREY coloured 4 wire plug. They cost around £80 each. The smaller sensors are for post cat use and have a BLACK plug. They generally cost around £40 each. Neither sensor is interchangable above or below the cat. These sensors can cause confusion at suppliers and indeed I`ve even had packaging marked incorrectly from one I ordered from Gendon. Take care then when you order new sensors to be quite specific about location and plug colour. My correct sensor came from David Manners although it cost £63. I was greatly relieved to find the salesman, David, had a good knowledge of these parts and sent me the correct part first time.
Last weekend Charlie got my car on his ramp and swapped out the defective sensor. As it had been in the new exhaust system for just one year, removal was easy and carried out using a 22mm Lambda sensor removal kit obtained via ebay for £13. An essential tool to have around when removing these sensors. The part change took just two minutes. A quick blast up the road to clear the cats and get them warmed up before we had a definate result seen using the Android Torque app once again. No more flat lining or rough graph readings. 39mpg achieved following the lorry with my boat on it up to Kent and much crisper performance as a result of the work. The car certainly appears to be using less fuel than it was prior to the sensor change.
Many of you will recall my struggles to rid this car of a flat spot when taking the car off from a standing start. All the usual things were actioned. Throttle and MAF cleaned, fuel and engine Terracleaned, new plugs and filters, vac and pressure pipes etc, etc. Certainly an improvement but still not quite right. Fitting this new post cat Lambda sensor seems to have done the trick. So best advice then would be to take a very close look at Lambda sensor performance if you find yourself with a sluggish car. I`ve yet to get the car on an exhaust car analyser to confirm where the emmissions now stand.
It has been a long road to find this well burried fault. Hopefully it is now fixed for good. Gas test results to be posted here in due course.
Mike
