Performance Enhancer Resistor?

I see that several people are selling resistors that they claim enhance the bhp of any petrol car with fuel injection system from 1988 onwards. Has anyone tried one of these and if so what was the outcome?

Where where where?

Presumably, these resistors are fully guarantied and the company will pay you any petrol not saved?

Never tried one, but it's mostly bullshit. They come in two flavours. The first one connects in with the coolant temperature sensor, and alters the real reading so the ECU thinks the engine is running cooler than what it really is. This means the ECU injects slightly more fuel to allow for the cooler engine, meaning slightly more power. This is all fine and dandy, up until the engine enters Closed loop running, and starts relying on the Lambda sensor for fuel mixture control, and the ECU starts trimming the fuel quantity back down (you could alter the temp signal enough so it never entered closed loop running, but it would run far too rich and choke itself).

The second option is if a Mass Air Flow Meter is fitted. You can fit a resistor to alter the signal so the ECU thinks the engine is getting more air than it really is, and also injects more fuel. Again this only works up until closed loop running cuts in. But it also has the drawback that any decent ECU will realise that the sensor reading is too high, and will log it as a fault (a 2litre non-turbo engine can only draw in aprox 1litre of air every revolution, if the ECU sees 1.25litres of air, it knows something is wrong).

These things also, typically, make the ignition more advanced. In theory this *may* give slightly more power, but it may also destroy your engine through catastrophic knock. You pays your money and you takes your choice...