Hi

I'm having some problems with O2 sensors and I need some help. I have searched other threads and read through them, and while the info has been helpful, I don't seem to be finding a clear solution...

I have a 2000 Discovery II, with 90,000 miles. I had replaced O2 sensors about 3 or 4 years ago, but recently engine light came on and codes indicated O2 Sensor (Bank 1 Sensor 1), so I replaced both front (pre-cat) O2 sensors. Then, after a few miles, I got more codes indicating BOTH front sensors and I assumed I had just received bad O2 sensors. So I returned them under warranty and replaced again (black box from Amazon with orange OEM connectors), and then after 15 miles or so, I'm now getting the following codes:I've checked the connectors and sprayed them with contact cleaner, I don't believe they are dirty or oily. I can't find any vacuum leaks (maybe I am missing something). Didn't see any wiring issues. Spark Plugs and wires were replaced 3 years ago.

When I watch the O2 status on a code reader, it is changing, but not by much, seems to stay around .2 for both front sensors?

I can't believe that I have received 4 bad sensors (maybe?), and I assume there is something else going on????

Could it be the MAF (I hate to replace it without being sure)??? Is there anything else? Maybe I am just missing a vacuum leak?

Any suggestions? Thanks!

Lee
2000 Discovery II
90,000 miles

 

Maybe an exhaust leak? Did you have to remove the y-pipe the get the sensors replaced, or were you able to do it in place?

I get the P1171 and P1174, and I'm SURE I've got an exhaust leak at where the y-pipe meets the manifolds. I can feel it when it's on the lift. I was going to try to tighten them up, but I noticed one or more of the studs are missing, so I just ordered 6 nuts and studs from rovahfarm. (I already had the gaskets) I'm hoping this fixes me up.

 

It is not your MAF.
As already mentioned, start checking for exhaust leaks.

 

I'll check for exhaust leaks, but I did not remove y-pipe when sensors were changed. Stupid question - I presume I'm looking for a leak before the sensors and not after(does this make sense) or does it matter?

I'm wondering if I have a connector issues, but seems odd to be on both sides...

Also, when I pulled the sensors the second time, they seemed pretty black with soot to have been in such a short time, but I'm guessing that is just a result of the mixture being off which is obviously a result of my problem.

I'll check for exhaust leaks (and also vacuum in case I missed something) and report back.

THANKS.

Lee

 

You're looking at it correctly, before the sensors is where you'd look for the exhaust leaks.

 

if cover your exhaust with a rag it should be pretty easy to find your exhaust leak

 

Look at the manifolds for cracks. The passenger side from my understanding is notorious for cracks, not sure about the driver side it is more stout. I have a spare driver side manifold if you do indeed need that. I would look at where the downpipe connects to the manifold, mine cracked on the driver and the passenger separated.

 

I checked for exhaust leaks and didn't find anything.

Looked again for vacuum leaks, didn't see anything...

When I first started the engine and looked at O2 data, Bank 2 sensor seemed to be switching pretty good, but Bank 1 seemed flat at .2. After I drove a few miles, both sensors seemed practically flat around 0 or .1.

Cleared codes and drove a few miles. Pending P0150 and P0130 came back fairly quickly. After a few miles P0171 and P1171... Also idles rough when in gear and smooth when in neutral.

Still stumped... I hate to try another set of O2 sensors, but seems like everything is pointing that direction...

Any thoughts?

Thanks

Lee
2000 DII
90,000 miles

 

So, since the 171 and 1171 come back, there is no question those 2 front 02's are acting up, not sure where to point you at this point.

 

Not trying to hijack the thread, but, Jafir, please report back if the exhaust work gets rid of 1171 & 1174. I've had them for a while and have mostly been told to get a smoke test. Never thought to look for an exhaust leak but that's on tap for this weekend.

Thanks,