Strange check engine/O2 sensor readings

[jsfordboy02]

My '96 sport displayed the check engine light, read it, bank 1 and 2 lean, changed the O2 sensors read it again and no problems. 3 days later the light comes on again, this time 2 pending 1 "bad", so I turn it off. Couple days later, check engine light, this time only 1 is "bad", turn it off. Now a couple days later both read lean again. Any suggestions? Barring a loose wire or bad connection, what could be the problem, I dont see the sensors going bad that fast on their own, is there something else that could be causing them to read lean? I think I have a SMALL exhaust leak in my EGR system somewhere and about a month ago I had to put in a new fuel pump.

 

[budwich]

those "indications" are usually never about the O2 sensors.... they are indications that the sensors are reading lean conditions which are more to do with fuel / air mixture and of course the usual suspect of leaks in your intake system... lots of posts.

 

[jsfordboy02]

Understandable. But i dont get why as soon as i replaced the o2 sensors and read the codes before i even started the car the codes were gone. On the old o2 sensors i could erase the codes and the next time i drove it they flashed back on. Now its so random when the check engine light comes on. It does a litttle rough every now and then, doesnt matter if the light is on or not.

 

[my98nnj]

It does (idle/run?)a litttle rough every now and then, doesnt matter if the light is on or not.

Again, a lean code isn't pointing to the O2 but rather the system they are monitoring. Air/fuel. The intake gaskets are a known failure item which causes the lean condition your o2's are picking up.

The fix is to replace your intake gaskets. As mentioned above, there are many many threads regarding this.

 

[jsfordboy02]

It got new intake gaskets this past summer. Could it have anything to do with the new fuel pump or egr exhaust leak?

 

[1AJeremyD]

A fuel pump failure would be a different code and EGR leak shouldn't make your truck run lean and would be a different code as well. Try cleaning the fuel injectors or having the truck vacuum tested again for the intake leak. Throwing a million O2 sensors won't fix the problem unfortunately

 

[jsfordboy02]

A fuel pump failure would be a different code and EGR leak shouldn't make your truck run lean and would be a different code as well. Try cleaning the fuel injectors or having the truck vacuum tested again for the intake leak. Throwing a million O2 sensors won't fix the problem unfortunately

Just run some Lucas through it? I use it on a regular basis thats why I figured it wasnt a dirty fuel injector.

 

[budwich]

Understandable. But i dont get why as soon as i replaced the o2 sensors and read the codes before i even started the car the codes were gone. On the old o2 sensors i could erase the codes and the next time i drove it they flashed back on. Now its so random when the check engine light comes on. It does a litttle rough every now and then, doesnt matter if the light is on or not.

well there is a little more to the odb system than "just turning on a light" so to speak. If you do some research on the overall system, you will likely find out why certain things happen (lights on, now its off, lights on, now its off, etc). Of course, it depends on the codes but in general, certain condition "register" a fault and then after "so many starts" are removed depending again on what the initial condition was. So perhaps when you turned your key on to do the reading, you crossed that "magic threshold" and the codes were "dropped". Having said that, O2 sensor can go bad due to "fouling" usually from ingression / burning of antifreeze which contains silicon.

 

[jsfordboy02]

The only reason that the check engine is off is because I am turning it off with my reader and it takes 1 to 3 days usually for it to turn back on. I really dont think its the intake manifold, I have no burning anti freeze/oil, my fluid levels are not changing or "mixing". I have a feeling I have some kind of vacuum leak or a sensor going bad or even a bad fuel injector because its so intermittent.

 

[jsfordboy02]

Buddys ranger had the same problem ended up being maf. Cleaned mine out, just cleaned and oiled my K&N maybe the oil goofed it up.

 

[jsfordboy02]

What if my engine isnt coming up to temp? would a cold engine reading cause it to run lean and trip the check engine light? What is the "valve" thing right at the heater box that has the heater hoses in it and a vacuum line? Mine is leaking a little out of that valve.

 

[Explodr94]

Could be you DPFE sensor. That could cause a lean condition.

 

[jsfordboy02]

Fixed, leaking o-ring where egr tube meets intake. just spray a little starter fluid around.

 

[jsfordboy02]

Now check engine light is saying bank 1 lean, Ive changed the o2 sensor and cant find any vacuum leaks anywhere, this is getting frustrating. Thinking maybe another sensor somewhere else. Ideas???

 

[my98nnj]

If bank 1 is lean you either have a vacuum leak or clogged injectors.
I'd be looking for the vacuum leak.

 

[desertsky]

It takes several occurrences for the lean codes to show again. Every time I reset mine (just to get rid of the light), it takes a couple of days for it to come back. It does this so that it isn't constantly coming on for short duration, transient conditions. You still have an intake leak somewhere.