Misfires when O2 sensors are plugued

[GEN 3 SHO FAN]

I recently changed my Y pipe and I put in the same time 4 new O2 sensors on it. Waiting for it, I was rolling with O2 sensors disconected for some time as I know they were bad (a lot less gas and heat spent).

Meanwhile, I resolved a light misfires at idle when I changed my old front Motorcraft coils. Since then, the engine was really smooth at idle like a swiss clock.

Until I put the new Y and plug the sensors... Now I have, again, misfires at idle.

I remember reading a post from Paul saying he had troubles with a precise O2 sensor wire at the rear of the motor (3).

Can it be other causes to this ? (I will eventually check the wires when time will permit.)

Is these wires are passing at the place where the main wiring toast on the rear head ?

Thanks,

 

[99sho-time]

my old wiring harness they got toasted on the tranny fill tube. the rrear o2s were part of it, as far as i remember only the upstream o2's determine the fuel. so downstreams wont cause a misfire

 

[GEN 3 SHO FAN]

If I found something there, are we able to change them or we have to cut them to replace a damaged section ?

Thanks by the way.

 

[99sho-time]

I replaced the whole engine wiring harness. It may be possible to splice in a new section from underneath.

 

[E1]

I have seen a wire chafed on one side and only causing a weak short circuit in the signal wire. Also seen coil wires melt to the rear valvecover and cause bad things.
The circuit might only be made if the sensor is plugged in and sending input signal back to computer.

Try going over the wires very thoroughly. If the wire is only chafed you may be able to tape it up or put some corrugated loom material over the top. If a wire is pinched hard by something, best to install new plug.

 

[GEN 3 SHO FAN]

If I have a misfire caused by bad o2 sensor wire, only green ones (upstream) can cause this ? Downstream inputs will not affect A/F ratio ?

I will also do a better check up on the rear harness which was sticked on the rear head when i bought the car. I wraped it with 3 differents materials but I never investigate into the harness to see if all wires was o.k. (winter job on the stack)

(Edit : I also another cause of this misfire but I'm not sure because I stored the car because fall is coming here. I will do another post with that. It can be an issue for others.)

Thanks,