Thread: Auto sparkies

Got one here that's a bit out of my league. Its an old jeep wrangler winch challenge truck that's had a efi six put in it out of a Cherokee, and what a rough job. It doesn't go no injector pulse and no spark, easy I thought crank angle sensors always give problems on these. Tried a known good sensor still no go so had a bit of a look at a wiring diagram and did a bit of reading, the sensor is a 3 wire and the earth apparently is pulsed on and off by the ecu. Anyone actually know if I cut the earth wire that goes to the ecu and just earth the sensor will It fry anything?

Current limit it first. Use a small 12v light bulb

My 2c


At an ‘informed but rough’ guess, it has what is known as a ‘sink input’.

Most traditional logic circuits have a positive voltage for high or 1, like 5V or 24V depending on the system, others have a positive voltage feeding to the sensor always, and connecting the negative or ground is what triggers the signal.

Basically imagine a simple 12V car battery, connected to a light bulb via a switch. You can put the switch in the positive or negative leg of the circuit, and it will turn the light on or off with the same effect regardless. In a car, if it switches positive and close to the battery, you have less ‘live wire’ in the system. Hence one reason, positive switching is more traditional.

I don’t know if your sensor is this or not, but it could be and hopefully the above might help you answer your own question.

The other possibility is that it earths from what is sometimes known as an ‘instrument earth’ or reference earth, separate from chassis or ground type earth, free of gremlin currents or back feeds. If it needs a What kind of sensor is it, as in what is it physically sensing to determine crank angle?. If it does require a reference earth, direct to chassis could cause wayward readings or damage the sensor.