Be Careful With Cheap Tuning Add-ons . . .
On eBay and in various car magazines you will find all sorts of little gizmos that claim to give your engine more grunt, better bhp or greater miles per gallon etc, etc.
Most of these "chips" are not chips at all, they are 2pence resistors placed in circuit with the air-flow meter or the water temperature sensor. The air-flow meter trick is to make the engine management computer (ECU or ECM) think that more air is being drawn into the intake manifold than actually is. This is done by altering the true voltage sent on the signal wire to the ECU and thus the computer squirts the fuel injectors a little longer and therefore more fuel enters the cylinders. This extra fuel may increase power a teeny weeny bit, but you are more likely to simply suffer less mpg.
The other trick, again using a resistor, is to cheat the ECU into thinking the engine is not fully up to running temperature and therefore, again, a little more fuel will be injected into the cylinders. I used to put this "mod" on the early Cavaliers and Astras with the Bosch LE2 injection system whose software was good until the engine had covered 40,000 miles or more. At about this time in the engines life, due to general wear and a little bit of "engine breathing", the software couldn't adjust the fuel requirements satisfactorily. This little trick worked well and cured the "flat spots" and generally poor throttle response.
HOWEVER . . . If your car is a 1992 or younger, forget the gizmos completely. Your car will have a device called an oxygen sensor (lambda sensor) inserted in the exhaust downpipe usually. It's sole purpose in life is to tell the ECU if the engine is running too lean or too rich. So suddenly, we have a problem . . . we've tried to artificially richen the mixture for more power. What is the oxygen sensor going to do when it sees this richer mixture? It will command the ECU to lean things off a bit until the mixture returns to it's designed ratios. Doah! We are back to square one again. Our little add on chip has done nothing.
The only time alterations work with any great success is on turbo charged engines when the boost is increased along with the all important re-mapping of the ECU to give more fuel in the correct proportions for the extra air that is being pressured into the engine by the turbo. This time the oxygen sensor is happy with things because now the air and fuel charges entering the cylinders are in the right proportions. Here enormous power gains can be found because basically by turbo or super charging an engine you are increasing it's effective capacity, i.e. a 2 litre engine when boosted by a turbo or supercharger suddenly becomes a 3 litre engine. Up the figures by further boosting and re-mapping and now we are getting some huge gains in bhp., but mind you don't overdo things and stress the roundy roundy or up and downy bits. You'll know when that happens . . . there's a huge bang under the bonnet and lots and lots of smoke! Impressive, but expensive.
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