Hi. I've done some reading on the forum about this code (P0306) and I'm trying to continue my diagnostic.

I have an 04 Discovery with 62,000 miles on it. I'm the second owner and the PO did valve cover gaskets around 48k and spark plug wires around 42k. I also have a pretty complete set of service records ranging from regular oil changes to a transmission flush. And, I always put 91 in it.

So, about 2 weeks ago the Service Engine Soon light came on and I got the code read...it was P0306. Did some reading and started with replacing the spark plug since I actually don't think they had been replaced. Two days later the code went away.

It stayed off for about a week until the Service Engine Soon light came back on a Saturday while on a drive to Tahoe for the weekend. The next day the light went off and stayed off for a few days.

When the light came back on it flashed about 6 times and then just stayed on. Next day it went off and then came back on again. It's been running very smooth, haven't noticed any funny sounds, no loss of gas mileage. I actually got 17.5 over the weekend to Tahoe. I have not gotten the code read since the light came back on.

I think the spark plug wires are 7mm but not sure on the brand, this job was done at the dealer by the PO. Is my next step to replace the wires?

I also see oil around the oil pan. I don't think the two are related but wanted to mention just in case. Any thoughts would be appreciated.

 

The oil is not related. The stock, gray, 7mm wires are total crap! They may work okay for a while but not for long. Do they still have the cylinder #'s on them? If so, those are the stock factory wires and they are probably shot. My Rover was dealer maintained and I don't think they EVER changed them or the spark plugs for that matter! It took me about 2 and a half hours to change the plugs the first time they were so stuck in the heads.
So, that's probably a good place to start, 8mm wires and a set of new plugs. Then reset the codes and try driving it again. Good luck.

 

Thanks. Yes, they are the gray wires. Just got the codes read. Now I have P0306, P0130, P0171. Will search for these.

 

Ok, looks like I got O2 issues. Will start with new plugs and wires. Will be my first time doing the wires but saw a write up. Any other pointers

 

The wires that British Pacific sells have numbers on them too (but the entire set cost less than one Rover wire). They are probably crap too, I'm not sure. I didn't know what I was doing when I bought them.

 

I just got 8 new Bosh Platinum +4 plugs. Will install those shortly. Napa said they needed a part number for the Magnecore 8mm wires. Anyone know?

 

Depends on which ones you want. For 99-04 DII the part number for the 8mm is 80242.

Go to MAGNECOR Race Wires: WELCOME TO MAGNECOR! and read up on them. Then click on catalog and go to page 18.

 

The o2 issues may be caused directly by the misfire. The plug doesn't fire or doesn't burn enouh of the fuel off and then you get an o2 code telling you that raw fuel is being dumped down the exhaust. I would just change the plugs and wires first, reset codes, then test drive and see what you get. If you continue to get the o2 and misfire codes, you may have to look into a possible head gasket job (maybe).
I just got a flashing "change engine light" the other day when I blew a head gasket and the coolant getting into the cylinder was putting out the fire on that cylinder. Not to scare you, just something to think about. Sometimes they go right around your milage. My DII has 145,000 on it so mine's probably just about ready to be done the second time. Good Luck with this, I hope it turns out to just be a bad wire or two.

 

Thanks for all your help. I've put in the new plugs and started her up...no lights as of yet. I'll be driving a lot this weekend so will see how it does. I'll get the wires at a later date.

Next projects are resealing the transfer case and new oil sump gasket.

 

Most of the time the transfer case leak can be cleared up by adding a bottle of White Shepard when you change the fluid in the transfer case. Then usually in about 2 days driving, the leak clears up totally. I hear it works great, I bought some when mine started leaking but I haven't put it in yet. It is expensive, I think it's like $20 a bottle or something like that but works for most oil leaks. I bought mine at Advance Auto Parts.