ok, read a few problems on this, here is mine. 2001 1500 5.9L. Start the truck runs smooth for 30 seconds at about 800 rmps. then starts to run ruff. after 4 minutes runs fine if it is drivin right after start boggs down and back fires...after about 3 minutes runs great... and will run fine untill shut down for about hour..did have a code.. think it was old...that indicated downstream o2...replaced it ...no change..does this sound like pre cat o2...

 

That sounds just like a pre-cat oxygen sensor. If you add that you can hear the intake sucking loudly you'll have the most common description right there.

 

Easiest way to find out is to simply unplug the precat sensor and see if there is any difference in how the truck runs.

 

atlrus, thanks for the info, unpluged the precat o2, truck ran great, no backfire or bogging down. tripped the check engine lite though. can i drive it like this for a couple of days unplugged? need a couple of days to come up with the 100 bucks to replace.

 

you could... if you wanna burn valves, and replace your motor.

the pre cat o2 controls the fuel fixture, and without that, you could run it either super rich, or super lean, both of whcih are bad things. for various reasons.

 

thanks, plugged back in, will replace in few days

 

Not true. A messed up O2 sensor will give you too lean/rich fuel, hence the misfire, which is more dangerous for your engine. You are better off driving without O2 sensor than driving with a broken one! The sensor does NOT control the air/fuel mixture, this is done by the computer, the O2 sensor simply tells the computer how much oxygen is in the exhaust.


You can safely unplug the O2 sensor until you come up with the $$$ to replace it. As a matter of fact, there are quite a few people here who drive without it on purpose

 

hahaha. thats one of the funniest things ive read, you obviously have no idea how these vehicles function do you?

heres a direct quote for you.
Maybe you need to read the FSM

"During Open Loop modes, the PCM receives input
signals and responds only according to preset PCM
programming. Input from the oxygen (O2S) sensors
is not monitored during Open Loop modes.

During Closed Loop modes, the PCM will monitor
the oxygen (O2S) sensors input. This input indicates
to the PCM whether or not the calculated injector
pulse width results in the ideal air-fuel ratio. This
ratio is 14.7 parts air-to-1 part fuel. By monitoring
the exhaust oxygen content through the O2S sensor,
the PCM can fine tune the injector pulse width. This
is done to achieve optimum fuel economy combined
with low emission engine performance."

are you still standing by the fact that the o2 sensor doesnt control the A/F ratio?

i do have to admit that the post-cat (downstream) o2 doesnt control jack schit, it just monitors the cats efficiency. this is probably the o2 sensor you hear about guys running with it unplugged. NOT the pre-cat(upstream) sensor.

 

Even if the upstream O2 is disconnected, the computer will use a conservative "default value" to keep the A/F ratio somewhat in check. This is to at least keep the motor running until you get your problem fixed. Unplugging your upstream O2 *shouldn't* hurt the motor, but I wouldn't trust the pcm default value that much. Get the $100 and throw a new O2 in there and be done with it.

 

Maybe you should read what you have quoted. The O2 sensor only provides information, it does not control the a/f ratio!

As I've mentioned in another post, we have drove my wifes tahoe for 100,000+ miles WITHOUT the O2 sensor, per our mechanic's advice not to waste any money unless we need sn emission test done. And i just went from Michigan to SC with both my precat sensors unplugged throu the mountains towing 8,000 lbs. behind me.

The lack of O2 sensor will only hurt you if you need an emission test done (or if you want to get the best mpg possible), while a wrong value i.e. a misfire will mess up your engine bad. So dont give advice when you have no idea what you are talking about!