Hey everyone,

i've only posted a few times, but have learned a whole lot from these forums! i have run into a problem that i can't seem to find an answer for. i just recently purchased a 2003 Land Rover Discovery (133,000 miles) and the previous owner had done the old "disconnect the Battery" trick before i bought the Rover, so no check engine light was illuminated on the dash. Once i got home the next time i started the Rover the check engine light came on. i ran the codes and it showed that i had a misfire in cylinder 4 & 6 & random.

i have replaced both coil packs, all spark plugs (Bosh), and installed new 8mm wires (Kings). i also went ahead and replaced the Mass Air flow sensor (Bosh) to rule that out. the old spark plugs looked to have normal wear and tear. I have the waterfall affect behind the dash and am going to work on getting that air out.

cleared the codes and drove around... 30 miles later the check engine light came back on with the same codes. Cylinder 4 & 6 Misfire with the random code. The Rover drives great, but I noticed that the misfire only occurs at my initial start-up/idle. I do have a rough idle sometimes, but not always.

Can anyone HELP ME, maybe DiscoMike?

 

Oil in oxygen sensor connectors.

 

you should check the o2 sensor at stated, but i fear you have bigger issues

 

There is a burnt O2 connection on the driver side. Looks like it touched the exhaust manifold. Someone's zip tied it back to the firewall. Is this a common thing to occur? When I get back home tonight I'll take a photo and clean the O2 connector. Thanks for the advice, hopefully this is it.

 

bingo, that would probably cause a problem like MLT suggested

 

Ok...so i could not pull apart the connector. It was melted together. I ended up breaking the connector and tryed to splice the wires together, but now i get the code that the O2 sensor is disconnected. Does anyone have a wiring diagram for pairing the wires up to the O2 sensor? I am going to go ahead and replace the whole set of O2 sensors. Does anyone know where i can find a new connector other than at the scrap yard?

I attached a photo of the burnt O2 sensor.

 

it is fine to splice them. you can even save money and buy them that are designed to be spliced with butt splices and shrink, rather than using a specific plug in connector.
so clean section of wires would be fine to replace melted junk

 

If you use butt splices get the perma-seal ones that you seal with a heat gun after making the crimp connections. This will keep moisture out so the connections don't corrode due to moisture, oil and coolant. Probably a good idea to cover the wires with high temp split loom, too. If you buy the generic O2 sensor there should be a wiring diagram inside the package.

 

Since i am replacing all 4 O2's could i simply use the old connector end of the rear sensor? i think i read on another forum where the rear is simply the reverse of the front.

Either way, can someone tell me what color wire matches to the corresponding wire for the O2 sensor. this would be for the driver side O2. A photo would be great if someone gets a chance.

 

Ok, so after some cuss words and bloody knuckles i finally was able to change all four O2 sensors. Looked like one of the rear's had been previously changed, but the other three looked to be original and were extremely burnt and clogged. The driverside O2 was the main issue and it looked like the previous owner tried to remove it at one point, but it was seized on. After three hours of unsuccessful removal and many broken tools, i said Fu*k it and cut the body of the O2 off so i could fit a 22mm impact socket over it. I used the WD40 penetrating oil and let it sit for a few minutes then coming from the engine compartment with three large 1/2" extensions and a universal joint i gave it one good tug and broke it free...well i thought i was out of the clear, but the last three threads broke off of the O2 and i had to take a pick and scratch them out. Didn't take long, it was just a pain.

My next repair was to re-wire the connector that had burnt on the exhaust. i was able to use the old connector from the rear O2 sensor and then spliced the wires back using Posi-lock connectors. These are great in line connectors! they are about a $1 a piece and are worth it. Since i used the old connector and wires from the rear O2 i was able to reroute the wiring so that it would never burn on the exhaust again.

Now i'm finished!!! My idle is smooth and the Rover runs like new. Wish i had started with the O2 replacement before i put all that time & money in the coil packs. Either way She's tuned up and ready to go.