The harness does two things.

1. Provides a constant reference voltage to the optical sensor.

2. Prevents exteraneous EMF and voltage surges from reaching the sensor. (Much like isolating the power source for hi-po automotive stereo systems so you don't listen to your alternator whine and sparkplugs crackle).

Since the difference in input and output signals is in millivolts, you can see how an accurate signal to the ECM is critical for determining fuel characteristics for the computer to compensate on the timing and duration of the injection pulse. You could run with out, but why run the risk of potential damage to either the sensor or ECM? ($$$)

This was posted on another web forum. Comments?

We need JD or TIM on that one....Big Guns

Louis

How 'bout 'the naked guns' - that blurb is correct, tho some OBD1 trucks did not require the filter, and most do not with upgrade to 5521 IP - symptoms are rough idle, fishbyte, hard-start.

The corollary to that is that unfiltered wiring can pick up pulses (induction is the phrase the cat5 guys use), and pulses in your IP means bizarre behaviour. That's why the filter was put on there in the first place.

Ergo - it will run without the filter, but you may get some occasional hiccups (fishbites). A worn filter harness will also give you fishbites.

A worm and some luck will give you fishbites, too. According to Fysh Guide.

Damage will not occur to either the sensor, or the ECM. Bad "data" being exchanged between the two points due to EMF noise, yes... damage no.