Multiple Cylinder Misfire

[cburwell at comcast.net]

Sorry for the line spacing, I guess Comcast's web client does not  automatically break the lines up.

Let's try this again:

I am trying to hunt down the source of what my ECU says is a misfire problem.

I have pulled the following codes from my ECU: P0135 (Front O2 sensor heater),
P141 (Rear O2 sensor Heater), and P0300 (Multiple cylinder Misfire). I also
recieved error code P0304 (Misfire on cylinder 4), but when I checked my spark
plugs they looked fine (White/brow/grey, which I presume is normal). When I
reinstalled my plugs I scattered their order and now I do not seem to get a
misifire code that pinpoints a cylinder but rather just the P0300 code.

I know my front O2 sensor needs replacing, as does my rear one because of the
P0135 and P0141 codes which tells me that the heater on both is malfunctioning.
 So I am currently pricing them for replacement.

What is bothering me is the misfire code(s), because my car does not feel or
sound like it is misfiring, and power delivery seems about the same. In the B15
 FSM it says that if the ECU detects a misfire that will harm my three way cat
(TWC) my MIL will blink, then on the second occurance of a harmfull misfire the
 MIL will blink again and then stay on from then on. Obviously my MIL comes on
 right away because of my O2 sensors, but at no point does it blink. This leads
 me to believe that the second condition listed in the FSM for a misfire is
occuring.

The second condition for a misfire is a misfire that is not threatening to the
cat, but rather one that will effect emissions. In this case the MIL will come
on after the second occurance of this misfire and stay on (at no point will it
blink). This leads me to believe that this is the type of misfire I am
encountering.

As I said the car does not seem to be misfiring, and my plugs look fine. In the
FSM under "Things to check" when a misfire occurs it lists "heated oxygen sensor
 1" as an item to check. Could this misfire code be caused by the the
malfuntioning of the front O2 sensor's heater? Remember I am only getting a code
 for the heater on the front O2 sensor, and not the O2 sensor circuit itself.

My car is a 2000 Sentra SE (RR SR20DE) with 34,7XX miles on it. I replaced my
plugs at 26,000 miles and my cap and rotor at 25,000 miles (In an attempt to get
 better gas mileage).

As I mentioned before I do not feel my car misfiring. I assume I would feel my
car if it was misfiring. Are there any other reasons why I would be throwing the
 misfire code? I searched and found a few threads, but no real answer as to what
 would cause the misfire.

--
Chris Burwell
2000 Sentra SE
http://home.comcast.net/~cburwell