Over the years I have seen a lot of money spent on the pursuit of extra horsepower. I’m not talking about people who look to gain the absolute maximum potential from their engine. People just looking for that little bit more, to give their car that little extra go. Looking at chipping DME’s, bigger exhausts and high flow air filters. They look abroad, so to speak, to get more horsepower when they could be looking at what they already have. I believe there are some commonly overlooked items that can have a significant impact on the tune of your car. Over the next few editions I will look at some of these areas.
This newsletter we’re looking at Oxygen Sensors.
These sensors measure the oxygen content in the exhaust gas exiting the vehicle. The oxygen level is dependant on the air/fuel mixture. The special feature of the oxygen sensor is that deviations in Lambda, (the perfect air/fuel ratio) lead to a change in the output signal of the sensor. The sensor consists of a ceramic body, the surfaces of which are fitted with platinum electrodes, through which the exhaust gas can pass. The sensor works on the principal that the ceramic material, which is doped with certain metallic oxides, becomes conductive at high temperatures. If the oxygen content on each side of the electrodes varies, then an electric voltage occurs at the electrodes. This voltage represents the measuring signal. The sensor is placed in the exhaust upstream of the catalytic converter, so that the outer part of the sensor can react with the exiting exhaust gasses from the engine. The inner part however is still in contact with the outside air. By sensing the exhaust gas composition (Lambda), the DME can then adjust the amount of fuel required very accurately. Over time with exhaust deposits the Oxygen sensors lose their accuracy and speed with which they can react. This in turn can lead to an increase in fuel consumption. The DME wants to inject as much fuel as it can for engine safety, if the oxygen sensor is slow to or doesn’t react at all, the DME will run the engine richer than it needs to. The richer the mixture, the more soot and unburned particles in the exhaust, the more deposits that end up on the oxygen sensor itself. Then the unburned soot ends up in the catalytic converter, that in turn blocks up, as the vanes to allow the exhaust gas through are quite small. This can lead to a partial exhaust blockage, and more lost horsepower.
Next time around we’ll look at Air Flow Meters.
Hints & Tips
Trickle Chargers – If your car only comes out on the weekends or once a month. There’s nothing worse than turning the key getting a dim flicker from the dash lights or nothing at all. Fit a trickle or maintenance charger to your battery that will keep your battery topped up and ready to go.
Cleaning your headlights – When you next wash your 944, put the headlights up and have a look at them. Where they sit when they’re down is right in the path of all the road grime off the front wheels. When a lot of 944 owners wash their cars they seem to forget this. The headlights miss out on a tub and the next thing you know is that it’s getting harder and harder to see at night.