So here's the story. I got a 1994 Dodge Ram 1500 2wd v6 3.9l Magnum, a couple of weeks ago I got a check engine light. The code was number 21, the o2 sensor. But I also had a hunch that the cat was pretty cloged. So, I started by gutting out the cat. It went well, then I welded it back on the truck. I went to buy a brand new 02 sensor. The hole for the o2 sensor was very rusted, so a capped it and installed the new o2 senosr. The sensor is sitting in the open on top of the tranny tie wrapped to a line that i found. So I did a test drive, got another check engine. It's number 51 , that means the mixture is lean. After driving it a couple of times, the check engine light does not seem to come back, but the truck on idle feel's really wierd. Like it wants to die. So im thinking the only solution is to install the o2 sensor back in the original hole so it can sens the flow... But even thoe my cat is gutted will it read a bad mixture? By the way the 02 sensor is before the cat, and there is only 1 oxygen sensor. Thanks for the help

 

try replacing the front O2 sensor if there is one on the 94 i dont remember.

If that does not work go to the search function and search the 02 sensor and one will come up where you use 2 spark plug non foulers(like $2.00) and drill one to 1/2 inch and screw the 02 sensor into it then into the non modified non fouler then into o2 sensor bung.


It moves the sensor up out of the unclean air and it reads it as clean, cool air

 

the o2 sensor is new, but it's not in exhaust it's hanging outside in the open. I tie wraped it to a transmission line so it wont be exposed to water or other things

 

Wait, why is the sensor sitting outside of the exhaust?

 

because the hole in the cat was very rusted and the threads were damaged, so I capped the hole and connected the o2 sensor so it will read atleast read the air and give a mixture.

 

Sounds like it is time to spring for a new cat.

 

FYI there is a guy on ebay that sells em, Magnaflow I think, madhattergurl, I bought mine from there, seems good and fit well, although I have YET to get this thing to run somewhat decently. Cat unrelated tho.

 

Sounds like your running WAY WAY rich. The puter can't compensate enough to eliminate the lean reading from the O2 sensor sitting outside like that. It will never read any fuel mixture. Uncap and install the O2 or figure out some way to get that thing into the exhaust.

 

get a tap and chase those threads so you can put the o2 sensor in the pipe.
flue hit the nail on the head. with the upstream o2 sensor out of the pipe, you're going to have some major running issues.

 

Well heres an update. I went to start her up this morning and it was running horrible. It sounded like it was taking to much air at once, it sounded like a vacuum cleaner. Anyways, im going to uncap the cat amd install the o2 sensor in the oem hole tonight and ill see what that gives me.