plug wires and sensor Q

[Detlman]

Sorry if this is a stupid question but I am going to ask anyway.

On my 89 there is a wire connected to one of the spark plug wires, what exactly is the info this sensor receives/sends used for and what would be the symptom if it were bad or disconnected? Could it cause a rough idle, flatspot, poor mileage? What exactly is the purpose of this sensor.

( wire connects around one spark plug wire, goes under manifold and there is a plug on a bracket that it plugs into )

Thanks in advance!

[jmc1590]

The sensor that is connected (or rather should be connected) to the #6 plug lead is the Cylinder ID sensor. It alerts the ECU when #6 fires and as such, establishes / sets the injector firing sequence.

As far as the pitfalls of a faulty sensor (or disconnected one), the ECU fires all injectors as a single batch. While my first thought was that this would cause a rich condition (twice the injector cycles instead of one), a functional O2 sensor should be able to tell the ECU to reduce the injector cycle time in order to compensate.

I've had a failed injector on an eta previously and never knew there was a fault. But that was Motronic 1.0, not 1.3.

Other thoughts?

[e30Derty]

would this cause my car to feel like it will die when I change gears and reach about 3-4000rpms? once I get to 4th or 5th gear and passed 50miles/hour it works fine, but I notice increased gas consumption...

[jlevie]

+1 to what jmc1590 said. And I'll add that the lack of that signal will cause a CEL, but no other problems.

A missing Cylinder ID signal won't cause the problems you are seeing. Those are more likely to be; intake leaks, bad AFM, fuel pressure/delivery issue, flaky CPS, bad O2 sensor, mis-adjusted valves, bad ignition wires/plugs/rotor/cap, mis-timed cam, etc.

[Liam]

NOTE:

On the 173 DME the lack of a CID sensor signal won't even set off the MIL (Malfunction indicator AKA Check Engine light) I'm not sure if the 380 DME will throw the MIL on though.

The only indicator (for most drivers) would be poor fuel economy.