Hey everyone...this is my first post on this site, and I hope I can get some of my issues resolved because I really like this truck and would like to keep it for some time. Just bought a 1995 chevy blazer LT 4.3L Vortec engine. She is crazy clean, and the previous owner replaced a TON of parts on her. I have been having some issues with her sputtering when I accelerate though. The last two weeks, I've have these codes pop in in this order:

P0300 (Random/Multiple Cylinder Misfire Detected)
P0303 (Cylinder 3 Misfire Detected)
P0141 (O2 Sensor Heater Circuit Malfunction Detected (Bank 1 Sensor 2)
P0141 (O2 Sensor Heater Circuit Malfunction Detected (Bank 1 Sensor 2)
P0303 (Cylinder 3 Misfire Detected)

I have run a bottle of Techron once already, and still no fix to the problem. She idles great, and keep a steady RPM just fine,....but when I accelerate, anywhere between 1,300-2,200 RPms....she sputters just like I'm getting a misfire.
Also, I don't know if this could be part of the problem, but my gas mileage has been pretty bad. I'm coming from a car with a smaller engine though. Around town,...first tank was 13 MPG's. Now, off a full tank of gas.....I'm down to 1/4 tank, and have only gotten 191 miles. Is that a normal range? Any help would be GREATLY appreciated. I'm planning on moving to North Carolina in three weeks and need this truck to be in top shape to pull a trailer, and make the 11 hour ride!! Thanks again!

 

either you have a bad plug or a bad wire which is causing the miss.

the bad O2 Sensor is on the drivers side, though it says circuit so it could be bad wires. replacing the O2 sensor while you're down there is up to you.

i'm sure a misfire doesnt help the gas mileage but a bad O2 will really kill it, i was getting about 40 miles less on a tank

 

the 300 code can be caused by a grocery list of things..

Dist cap + Rotor
Plug Wires
Spark plugs
Vacuum leak
Leaking or stuck injectors
Bad Fuel pressure regulator
Fuel pump
Worn Distrubuitor
Carbon Build up
bad gas
EGR valve Sticking
Plugged exhaust
and a few other things

as for the o2 sensors, your going to have to check the heater circut, *HINT* search feature works wonders for codes.

With a little basic diagnosing and some searching around the forum you will be able to figure it out! Good luck!

 

If the missfire happens every time, and not just a percieption, every time. Then it is something that doesn't change as they get heated up(spark plugs,wires,dist cap,(vaccuum)) The bad O2 sensors are definetly not helping your problem but you should also look into seeing how much vaccuum you have (around 17 in of Hg). A tune up would definetly be in your best intrest especially if you don't know when the last one was.

 

Your truck should have two O2 sensors. B1S1 is the upstream sensor. B1S2 is the downstream, post-cat sensor. B1S2 does not impact engine performance in anyway and is a catalyst monitoring sensor only. You can try swapping the downstream O2 sensor with the upstream sensor and see if the code changes to P0135. If it does, you know that the sensor is bad. If you find that the sensor is bad, replace it with a new AC Delco AFS75.

Just a thought, but have you replaced the fuel filter? How about a full tune up consisting of plugs, wires, cap, and rotor?

 

just wondering whats the diffrence between ASF75 and ASF105???

 

The subject vehicle requires the AFS75. Your truck requires the AFS105. Could be anything from wire length to a connector difference.

 

oh, intresting. i allways thought that all the second gens including the 95 had the same o2.....i guess its true, you learn something new everyday!

 

Looks like after putting close to 60o miles on her....the problem is starting to correct itself....am I going crazy? Got to my truck after a four day work schedule, and it was raining and humid out. The stuttering on acceleration has all but a little gone away. Only on slight occasions will she sputter now. I was thinking along the lines of fuel filter, or possibly a fouled plug,.....but now, she is getting better gas mileage (increase of about 25 miles), and is running smoother. Any ideas?

 

yeah i had the same things happening, after i fixed it, i had to drive it aroudn to get it all out.

occasionally now it will pop or backfire under load, but my guess is its a bad plug/wire, or one of them is just not connected tightly