Chrysler Repair: re: 85 lebaron (slow acceleration,etc), porcelain tower, head gasket

Question
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hi roland---thanks for responding so quickly to my question!  i tried the self diagnosis and came up with 2155, that is, there were only two sets of flashes, of 2 and 1 each, before the 5 flashed twice.  hope i did it right.  thanks again!  pam

Answer
Hi Pam,
The 21 code means that the signal from the oxygen sensor, which is mounted on the exhaust manifold, is out of the normal range. This could either be due to the electrical connector being open or not making a good connection, or it could mean that the sensor is no longer functioning. As the result, the engine logic controller subsitutes a mid-range value that is a compromise so the mixture of air to fuel is not optimal. This could be a part of the reason for your engine performance to be degraded. So look for an item that looks like a spark plug with a black wire comming from its tip to a disconnect plug and see if the connection seems clean and tight when you separate the two halves. If it is o.k. and the car still runs poorly, then replacing the sensor is probably worth doing. These have a finite life time, and when the head gasket blows the coolant that gets into the exhaust system may poison the sensor. So with your engine's history it is not unreasonable for the sensor to be bad. But do check the wiring first to make sure it was reconnected by the shop. It is fairly easy to remove, but you will want to put some penetrating oil on the threads and let it sit for half a day because they are usually pretty tightly stuck in the threads. So also use a wrench that fits tightly on the flats so you don't round them off if you do this yourself. The new sensor should come with a capsule of anti-seize compound so that it will be easier to remove when it wears out. You need to be very careful when you put it in to get it threaded straight into its socket and to not put any stress on the porcelain tower or the wire or you can damage the sensor so that it won't be of any use. They make a special slotted socket for installation, but you can likely use a box end wrench just as well. Torque it about the same as a spark plug (15 ft-lbs).
If that doesn't fix the problem, then I'd take it up with the shop that did the head gasket.
Roland