Hey everybody this is only my second post so I'm still getting the hang of it but I have a question (I'm also only 17). I had my stuck o2 sensor replaced when I started getting a code 13 and the check engine light came on and off on the highway one day (over a 20 minute driving period). So far everything appears somewhat normal since replacement but I still have a code 13 (along with 16 mpg)! I don't know if this has anything to do with the code but when slightly accelerating sometimes my exhaust makes a lower muffled kind of sound. I thought maybe the catalytic converter was clogged or something (also had the muffler replaced last september). Does anybody have any suggestions?

pull the o2 sensor & drive the car,if it runs much better, it has a clogged cat,, this allows the exhaust gas to escape thru the hole ,, your neighbors may not love you.
is the cat welded on or bolted
does the car seem to run strong ??
make sure the spark plug wires are not grounding on metal or touching,running along together
do not use a bosch 02 sensor

is this a V6 or a duke 4 cylinder

[This message has been edited by uhlanstan (edited 01-29-2014).]

Well the car feels sluggish (2.8 btw) but I'll remove the o2 tomorrow since I don't have the removal tool now. I think the cat is bolted on but I'll have to check again. I did unplug my new sensor and ran the car earlier and it felt like their was no difference (no check engine lights came on either and I had the car running several minutes). Finally I do have a bosch, I know most people recommend the denso's but does brand really make that much difference? Oh and the wires all look good too.

[This message has been edited by PribanicS (edited 01-30-2014).]

I would agree with the others in checking the Cat. On a Fiero you should be able to use a 7/8 wrench for the O2. Especially if it is fairly new.
Were you getting the 13 before or after the O2 replacement? O2s normally go open or just get weak and cause a code 44. In past experience, found most code 13s caused by a broken O2 ground. It goes to the same mounting point as the ECM grounds but it is normally tan not black.
Get a Denso or Delco. On Gm I consider Bosch Botch.

[This message has been edited by cmechmann (edited 01-30-2014).]

Yea the code was there before and after replacement. So where exactly is the ground? I'm not very location savvy in locating everything

They are supposed to be on the transmission to engine bolts. Sometimes they are attached to a head bolt.
Looking from the driver's side, with the throttle body towards you. Look down behind the exhaust crossover pipe for the bolts that connect the transmission to the engine. To the left side, there should be 1 or 2 bolts that have a stud built on to the end. The grounds should be there. If not look at that same end of the heads. Should be able to see 2 of the head bolts on each head. If any are stud type bolts, look there also. Rarely sometimes they will connect grounds to a bolt in the side of the block just over the transmission side of the starter.
This ground has a habit of getting broken when someone has removed the transmission. If the wire had broken and they didn't know about it, it confuses them because it is a different color than the rest of the grounds. Older Fords O2 ground was orange.(go figure)
The ECM applies around .5 volts to the O2 sensor. Because it is such a low voltage it uses a separate ground so the voltage regulator in the ECM can put out the correct voltage. O2 sensors will add just a little when rich and drop just a little when lean. Without that ground The ECM always gets a crap reading because it sends the O2 the wrong amount of voltage.
Another way to check this is to take a reading on the ECM side of the O2 sensor connector ( O2 disconnected) with the key on engine off. It should be around .45-.55 volts. With a bad ground it will wonder.

Hey thanks for the O2 grounding tip, I found it then took it off and cleaned it with a wire brush and guess what!!! My code 13 is gone now. I'm hoping this will be the fix for my bad fuel economy but I won't know till my next fill up. Thanks for the help people.

quote Originally posted by cmechmann: They are supposed to be on the transmission to engine bolts. Sometimes they are attached to a head bolt. Looking from the driver's side, with the throttle body towards you. Look down behind the exhaust crossover pipe for the bolts that connect the transmission to the engine. To the left side, there should be 1 or 2 bolts that have a stud built on to the end. The grounds should be there. If not look at that same end of the heads. Should be able to see 2 of the head bolts on each head. If any are stud type bolts, look there also. Rarely sometimes they will connect grounds to a bolt in the side of the block just over the transmission side of the starter. This ground has a habit of getting broken when someone has removed the transmission. If the wire had broken and they didn't know about it, it confuses them because it is a different color than the rest of the grounds. Older Fords O2 ground was orange.(go figure) The ECM applies around .5 volts to the O2 sensor. Because it is such a low voltage it uses a separate ground so the voltage regulator in the ECM can put out the correct voltage. O2 sensors will add just a little when rich and drop just a little when lean. Without that ground The ECM always gets a crap reading because it sends the O2 the wrong amount of voltage. Another way to check this is to take a reading on the ECM side of the O2 sensor connector ( O2 disconnected) with the key on engine off. It should be around .45-.55 volts. With a bad ground it will wonder.