It’s good to listen ! This applies as much to engine tuning as to life. Crypton tuners don’t detect a lot of faults, many only come to light by listening. For instance an air leak to the inlet system before whatever device that detects the air quantity being used on any car will cause running problems. This fools the air metering device into putting less petrol into the engine than it should and so makes the fuel mixture run weak. In it’s terminal stage this also results in an idle speed that is too high and cannot be brought down by adjustment because idle speed is controlled by restricting air supply to the inlet and the leak is by-passing this system. Some leaks are easy to find - they whistle, squeak, or even sing to you like Pavorotti. - but because the noise echoes around the engine compartment it is very useful to use a stethoscope to pinpoint the source. These sort of leaks are caused by a large leak confined to one small area, more difficult are the sort that leak a small amount over a large area, for these the use of an ultrasonic detector is invaluable, this picks up on the ultrasonic noise generated from when air movement exceeds the speed of sound as is the case from a high vacuum source leaking across to an atmospheric pressure. Usual areas for this sort of fault is the inlet manifold to cylinder head gasket joint and carburetor flange gaskets. Most difficult of all are where not much pressure difference is at the leakage source such as on fuel injection inlet systems between the throttle butterfly and the air flow meter - neither ultrasonic detection or listening will help you here, inspection of suspected parts is the only way. So when your car or partner doesn’t seem to be making the same noises as before take heed. Get out the stethoscope, the ultrasonic detector, and if this doesn’t work then remove a few things and inspect them.

Still looking at reasons for high HC levels causing an MOT   failure?.  An air leak via a leaky gasket,seal,or even a brake servo unit   with a poor diaphragm can make the mixture so weak on one or more   cylinders so that the CO will pass but the unburnt petrol left will   cause an HC failure. Other non ignition faults can be incorrect valve   clearances, cam timing wrong, modified camshafts, collapsed hydraulic  lifters,blocked exhaust,or if the car is a Metro a design fault that   causes the car to fail at idle but should pass at the allowed retest   speed of 2000 RPM.   Ignition faults that can cause high HC are all ones that cause either the   wrong amount of spark to occur or to occur at the wrong time. Such faults   can be sparkplugs gapped wrongly, faulty sparkplug(s),fouled sparkplug(s),   wrong type of sparkplug, faulty HT leads, distributor cap, rotor arm,or HT   coil,excessive ignition timing variation between cylinders caused by  distributor wear/engine management system. Apparent sparkplug problems   may have nothing to do with the sparkplugs though - a leaky head gasket,   valve oil seals,or poor piston rings can all cause the best of plugs to   fail.

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 remane the same then the ECU is most likely at fault. For more information on ECU testing click on ECU

Hessitation, power loss. This type of problem can be one of the most time consuming faults to find because the problem often is only slight and the fault only shows up when the car is being driven under load.

One of the most commen causes of this is fouled or sticking injectors that can be reconditioned at less than tenth the price of a new set. For more information on injector servicing click on injector.