P0300 is just a generic misfire code.

Then the P030X is the specific cylinder number.

 

So this code will usually show up with any cylinder misfire codes. If I had a misfire in cylinder 5 I would probaly get this code p0300 as well like I'm getting it currently with my cylinder 7 misfire. Thanks cappedup for all your answers.

 

As I understand it, yes. Seems a bit pointless to me showing both codes, but maybe there is a situation where it makes sense to throw 'just' a P0300.

No problem. good luck tracking it all down.

Last misfire I had was a really easy one. One wire had come out of its little clip and touched an SAI tube. Burnt through and shorted. Try just following and inspecting every mm of wire #7. From plug to coil. Easy fixes are the best.

 

Yes, a bad O2 can cause misfires, despite Disco Mike saying it is impossible, but in my experience misfires caused by a bad O2 are generally on multiple cylinders.

I would say still start with the wires and plugs, but you have just done both. It is possible there's a problem with your number 7 wire, even though it's relatively new. Happened to me.

 

Dont say that too loudly, you may get banned.
Happened to me. twice....

 

I guess to be fully helpful by cataloging my former problems, here is what I have experienced for misfires, especially with a p0300 code:

1. Head Gasket with coolant loss - if you are SURE you have a head gasket problem, get the manual and some tools and replace in a weekend for about $200. Try everything else first.
2. MAF (it does strange things when it fails... DicoMike fixed me up on this one) - I have a buddy with a Disco II so I borrowed his MAF; the fix was instantaneous. I have had good luck with the super cheap MAF on Amazon; about $40.
3. O2 sensor - this is another odd one... I don't know how it can cause misfires but I have verified that a bad one can, indeed, cause misfires (as I noted above).
4. Spark plugs and wires - easy to check... just move them from the misfiring cylinders to another cylinder and see if the misfire follows.
5. Coils - I always have a spare and have swapped them; they are in a terrible location and pain in the behind to swap. The coils have never been the issue for me and I still have my original, 16 year old ones in the truck. New coils are about $150-350. If it was your coil I would expect all of the cylinders served by that side of the coil to be acting up, and not just 1 and 7.
6. Connector off - check wire connectors on both sides of the coils to be sure they are tight, and to the silver cylinder ion the top, back, driver's side of the upper intake (top of engine).
7. Fuel injector issue - not likely.

The sulphur smell the OP mentioned means that the fuel mixture is too rich (because of one of the other problems) and the cat is, eventually, going to fail because of it. Too much gas disintegrates the cat, because the cat can't fully burn it. My guess is that your gas mileage is not very good right now.

1 and 7 are on the same side (drivers side) of the engine, and far apart, so I would not suspect a head gasket. Two spark plugs going out at the same time is unlikely, but that's an easy check by swapping the 2 and 8 to 1 and 7. If nothing changes, then swap the corresponding wires. I wouldn't suspect the coil because it is just 2 cylinders. with the rich running and p0301 and p0307, I suspect the MAF, O2 sensor, or a clogged catalytic converter.... or some other gremlin.

But I am not a mechanic... I am just a guy who has seen his rover through many problems and has replaced all of that stuff (including the cats) trying to figure things out, since I am a long way from a dealership.

 

I think he only has the misfire on 7. Not 1 also.

Drowsapp started that rumor Unless in one of the OPs other threads he mentions a P0301.

 

No that was me misreading the p300 as a p301

 

Oh heck well if he only has a real misfire on one cylinder, and it is the back one (by the water passage) the head gasket ooches up the list a little. I'd try all of the other suggestions first though.

 

Turned out to be a bad coil, switched it and the truck is purring like a kitten. Now to fix the rear bumper, paint wheel arches, replace some window trim, change brake pads, change power steering fluid, and then and then and then and then.....