The most baffling faults on cars can be caused not by the car but by people. When we have a car in for fault diagnosis we always try get as much information about the car’s symptoms as possible, and also about who has done what to where. We often find that while attempting to cure the original fault others are created, sometimes the original fault has been cured but the ones created remain. This was the case with an Audi the owner had a problem with breaking down intermittently and had changed lots of components on the ignition and fuel systems (At great expense – cheaper to have an accurate diagnosis of the fault) before the fault was cured. Unfortunately another fault appeared after all this work, the car would stop unless the petrol tank was filled above the ½ way mark on the gauge. We tested the fuelling system and discovered that the petrol pump was not delivering fuel when the tank gauge registered below ½ full, although the pump was running. At first we suspected a faulty gauge sender unit in the tank, so we removed and tested it, and checked that there was in fact the amount of petrol in the tank that the gauge said. All ok here. The petrol pump on this model is immersed vertically in the petrol tank, and suspecting now an air leak into the pump at the ½ full tank level we took the pump out. No air leak found and bench testing the pump was Ok as well. Baffled now we went to put the pump back into the tank when we noticed that the pump didn’t seem that long in relation to the tank depth. We got the tape measure out and found that the point at which the pump pickup sat in the tank was at about the ½ full point. Checking the part number on the pump showed it to be the wrong pump – the correct pump was a lot longer and cured the fault.

Our Audi 80’s get up and go just got up and went. The engine would idle fine but as soon as the accelerator pedal was touched it just laid down with a little moan and died. The car came to us from another garage that had given up on finding the fault, they thought it might be trouble with the injection system though so the first checks that we did were to make sure this was working ok. This checked out ok – fuel pressures were good and injectors were not blocked. After running through the rest of the settings for the engine we were baffled as well – everything checked out ok to the book but it still wouldn’t go. The clue to solving the problem though came from the engine vacuum – it was so low that we thought our gauge had packed up. Something was badly wrong with the valve timing or ignition timing., even though all of the engine alignment marks said that they were all right. We ignored all of the manufacturer’s marks, made our own , and after setting to our marks the engine ran brilliantly. We couldn’t leave it at that though because something must have happened to allow the manufacturer’s marks to be wrong, so we stripped the timing gears down. There we found that a timing pulley was damaged allowing it to rotate independently of the shaft it was attached to , making nonsense of the timing marks. A new pulley was fitted, the engine set to the proper marks and the get up and go was restored.

Emissions failure.  The most common cause of rich running faults is the lamna sensor or the ECU (engine control unit) both of these parts are relatively simple to check,  to check the ECU strip back the insulation onthe signal wire from the lamna sensor, this wire is usually black.  Then hold the bare wire between you finger and thumb then touch your other hand on to the battery positive if the emissions come down then you have a faulty lamna sensor but if the emissions remain the same then the ECU is most likely at fault. For more information on ECU testing click on ECU