Hey guys, Ive looked on Advance Auto parts site for the o2 sensors on my 1991 3.9 Auto Dakota and they are only giving me the "Upstream" one. From what Ive researched there are two o2 sensors no?? ..one being before the Cat and one after the Cat..correct? Do these o2 sensors have the same part number? If not can someone provide me a part number and/or place to purchase the one after the Cat?

I"m narrowing down my trouble shooting on the 3.9 by replacing parts! lol hopefully this process will fix what I believe to be a sensor problem.

*Symptoms: Under load the truck has really noticeable and loud valve chatter. I have put premium 93 octane in it and ran it for 30 miles so far and under acceleration it still pings/chatters excessively(thinking it may have been bad gas or cheap gas). Timing is perfectly set at 10* as recommended by manual. Im hoping this isnt a sign of a leaking head gasket or something of that nature. I have not adjusted the valves. Im starting with the o2 sensors and then the EGR valve as Ive read those can cause problems with gas/air mixture that may cause the chatter/pinging.

In the last month I have replaced the following when the truck died unexpectedly on me:
* all new distributor which includes the pickup sensor
* coil
* wires
* all plugs
* cap
* rotor
* fuel filter
* ASD relay
** replaced the water pump as well as it was leaking threw the weep hole pretty bad.

Thanks ahead of time!!

 

Just found out the ole LA blocks have a none adjustable valvetrain so that illuminates one possibility of the valves needing adjustment.

 

Bump ^^ Still experiencing excessive valve chatter. Have not replaced the o2 sensors yet but I have deleted the EGR and disabled the smog pump. I made a delete plate for the EGR and I plugged the vacuum line associated with the EGR. Any input would be helpful.

 

As a note - on pre-OBDII vehicles, typically there's one or two O2 sensors - either one for the whole engine in front of the cat, or one on each bank of a V engine, again in front of the cat.

The "Downstream" is for the cat efficiency monitor for OBDII.

So for 1991, I'd only expect two upstream - and then checking Dodge, the V6 got one upstream (!!!)

RwP

 

Thanks for the info. I may just locate em and replace em just to be sure its not that thats messim with the computer and possibly causing the chatter.