Leaderboard

Thanks all who have provided hints and tips thus far,it really is appreciated. The latest news in this saga is as follows: Battery disconnection/reconnection didn't really make much difference but worth a try. Bought a cheap code reader and got codes P1111 (Intake Air Temperature Sensor Circuit Intermittent High Voltage) and P1646 (O2 Sensor Malfunction Bank 1 Upstream). Note, this is less than a week from taking it to local Jag dealer who charged me nearly £100 simply to say the ECU 'won't communicate'. Grrrr! After clearing codes, the P1646 re-appeared soon after with MIL light back on again. Looked into various forums and found contradictory posts about which bank and whether it really was upstream/downstream etc. Decided to look further in code reader with real time data whilst driving. Found that Fuel Systems 1 and 2 stay in "OL" mode whatever happens. Also found Fuel Trims stay fixed at 0% and both downstream O2 sensors have 'stuck' readings (for current and voltage readings) that occasionally become unstuck and then stuck again. Checked o2 sensor fuse and relay and they are fine. Worked out (I think) what some of the cypher language used by the code reader actually means. (had to do this because the instruction manual doesn't cover this and its taken me most of the weekend). I think what is supposed to happen is that the after start up, the ECU causes the engine to default into "OL" (open loop? control mode i.e. no sensor feedback to make adjustments). After about 15 seconds or so, the sensors have been read and providing there are sensible readings, the ECU goes into "CL" (closed loop? mode i.e. thereafter making adjustments to fuel inputs via the injectors, on a near continuous basis according to feedback from the sensors (MAF, MAP, O2 etc.).The adjustments are called "short/long term fuel trims" and are measured as a percentage from the open loop default value and these adjustments help ensure minimum CO emission and as close to a Lambda (stoichiometric ration index) of 1.0 as reasonable. The problem in my case is that the CO is too high (1.5%) hence failing the emissions test. Now, 1.5% would have been a good result for my old 245DL Volvo from 1980 which was permitted up to 3.5% but that old skool vehicle was designed as open loop. I thinks what is going on is simply that the ECU does not get sensible values from the O2 sensor(s) at start up and as a result it stays in "OL" mode which causes the fuel trims to stay fixed at 0.0% i.e. the ECU simply ignores the sensors and thus no adjustment are made. So, with what I can make out to be sensible readings for Mass Air Flow, Manifold Pressure, Throttle Position and non-sensible readings from O2 sensors I have just ordered a whole new set of O2 sensors (simply can't get enough clear information about which sensor is duff). Will post again with result of replacements. Regards.

Hello Gareth, i had a similar problem with mine.... and a well know motor factor. When changing a the top hose / heater control valve / the Radiator (id only planned on the heater control valve - but....one thing leads to another scenario) i noticed it (the belt) had cracked severely so knowing the headaches one of those causes ( I also have a Land rover Disco) i decided to change it. Asking the motor factor if in stock by phone....yes we have and they've got two different ones both apparently for the car. How can that be i asked? Reply being don't know! I paid for both and set off to deal. I compared them to the one that was on it and we had three different sizes the biggest difference was about 120mm smallest was 85mm... but nothing remotely near mine. Added the fact that mine didn't have a number on it so that made it a bit tricky to ID. I went back to motor factor with all three belts and we tried to sort. They admitted defeat and refunded the money. I then called local Jag dealer. Yes we have one was the reply. It was twice the price but matched my original. The slight complication in all this was that my Disco was also off the road so out came the push bike for a 28 mile round trip.

Hi Gareth, I replaced my belt during a service, and TBH I have had hassles ever since. It was really tight and a bugger to fit, and I've been getting a variable and intermittent squeak since then. I'm starting to suspect this is the tensioner, but I'll need to conduct some tests to be sure. It could be it's slightly the wrong belt, which caused the additional tension and the squeaking, but my spares supplier is generally reliable in these matters. I don't have the part numbers at hand to check. Hope you get it sorted, Russ