Hello all,
A couple of months ago my service light came on with p0304 cylinder 4 misfire. I replaced the plugs and wires with Bosch +4 and Magnecore 8mm wires. Cleared the codes and they were gone for a couple of weeks. Then a couple of days ago my service light came on again along with rough idling. Codes were:

P0304 cylinder 4 misfire
P0130 o2 sensor malfunction (bank 1 sensor 1)
P0171 system too lean
P1171 manuf. specific

So I'm guessing my o2 sensors are bad. I'm thinking my bad o2 sensors are also the cause of the misfire? According to this http://www.obd-codes.com/p0304 bad o2 sensors can cause misfires. So I guess my next step is to replace the front o2 sensors. Just wondering should I replace both the front sensors or can I just replace the one that's bad? Anyone have any thoughts on this matter? I really hope the misfire is a bad o2 sensor and not a bad coil pack. (ease of labor) Also I don't know if this is relevant or not but my light and rough idle came on after I filled up at Conoco gas station (premium always), but I normally fill up at Shell (better quality). Any help would be greatly appreciated!!
thanks

 

You should look at the other thread on this. It may actually be a bad coil pack.

I just had an issue where I had rough idle and the SES light was on. Didn't get a chance to pull the codes, but I replaced the spark plugs with autolite double platinums and it fixed everything. Took about 3 days for the SES light to go off and no more problems.

 

There have been alot of people lately having problems with mis fires after installing the +4 spark plugs.

It could be you got a tank of bad gas.
To rule out the spark plugs go and buy a cheap set of copper plugs and throw them in, reset the codes and see what happens.
This will cost you about $12 and 30 min work.
O2's cant be replaced that cheap, and yes, you must replace O2's in pairs, both fronts, both rears, it is best to replace them all at the same time.

 

Hey, i had the same exact codes. I replaced my O2's and the rough idle went away as well as the misfires. On top of that, I am getting about 100 miles per tank more than i did before.

 

I don't think it would be too common for bad O2 sensors to cause 1 cylinder misfire. Your truck is running rich really on one side though so maybe that and a combination of the plus 4's.

 

First. how many miles on the engine and what octane do you run?
We know it is "NOT" plugs are wires since you had the same misfire before. 1 cylinder will not misfire because of 02's, the whole bank would have to be missing for 02's to come into play. If you are near or over 100,000, I would replace all 4 02's to improve both banks air to fuel ration and over all performance.
That being said your 340 is the cause for the 171 and 1171 so I would start there then you need to see what is going on with #4 which is on bank 2. I would suggest you first look at the plug for color, moisture and smell, then do a compression test and possibly a leak down test for for either a burned or carboned valve or head gasket leak.

 

Mike,
I have 85,000 miles and always use 91 octane. Yeah I agree, I'm thinking the Bosch +4 aren't the problem because I had the misfire before. I would like to note that when I replaced my spark plugs with the Bosch the existing #4 plug was in pretty good condition (no smell, color, moisture). Can we rule anything out? I will start with the o2 sensors.

Shane83,
It makes me feel better about spending money on o2 sensors knowing that resolved your problems.

Does it matter what brand of o2 sensors to get? I found some Bosch o2 sensors online for $64.00. I read somewhere that the factory sensors are from Bosch. That's the cheapest I found.

Thanks all

 

I was getting multi misfires and after changing the O2 sensor, they all went away... it was not specific to one cylinder though..

Just my 2 cents,

 

What O2 codes did you have though? P0130 is not a dead O2 sensor but is a sensor with a stoichiometric ratio that is not expected. Could be that the O2 sensor is going bad or could be something else. Like Mike said a compression and leakdown test would be useful. You could also swap the 2 front O2 sensors and see if the code goes away or comes back somewhere else.

 

Don't have the equipment to do the compression or leak test, but I'll look into it. Is that something Autozone can do? My plan is to start with the front o2 sensors, based on my mileage it wouldn't hurt to do anyway. Will do the rear sensors in the near future. I'll see if switching back to Shell gas does anything too. Keep you guys posted.