Hi, I have a sapphire Cosworth and I bought a narrowband Air/Fuel Gauge and a 3 wire Oxygen sensor to I connected the Red wire of the gauge with the red wire of the oxygen sensor together to an ignition main, the gauge and sensor black together to ground and the violet of the sensor with the gauge. Whenever I turn on the headlights the reading shifts two LEDs to the left. the sensor is only connected to the gauge not to the ECU. What could be the because an electrician told me it could be the gauge or sensor are faulty but they are both brand new.

 

Narrow bands are useless, as they only indicate a lean or rich condition (i.e. either side of lambda 1) and nothing in between.

You need a wide band.

As to the question, the reason is voltage drop.

I suspect you have spliced into the car loom and hence when you apply a heavy load (i.e. headlights) it results in voltage drop.

Martin

 

Get a good gauge like aem or innovate
Regards

 

The O2 sensor and gauge are connected directly to the ignition only them. I have an Auto-meter one.

 

I have wideband aem in my car and its connected directly to the battery via a 12v relay. The only cable I took from the car loom is the trigger cable. Specially innovate wideband if your voltage is low you have alarm in your gauge,it doesn't work properly. That's why my aem wiring connection is independent from car loom
Regards

 

It could be a bad O2 sensor? If i disconnect the sensor from the gauge an led turns on an whey i turn on the lights of the car it doesn't affect it like it does when the sensor is connected.

 

Probably because you don't have the load of the lambda? You state that it's only when you apply a heavy electrical load the issue arises, therefore to me it's probable this is voltage drop.

Cosworth's suffer a lot of electrical issues now, which is age related to the wiring.

One common cause of poor voltage is resistance in the fusible links (for which there are two) in the fusebox supply.

All you need to do to verify, is measure the voltage to see if the lambda is getting the correct voltage.

Martin