Advise needed,
I have just bought a 2000 XJ 4.0 and now doing all the basic maintenance, fluid, sparks...I thought everything went alright until I noticed a horrible fuel economy, less than 10 mpg.
I ordered a new coolent temp sensor and a new upstream o2 sensor. To my big surprise both o2 sensors has been canceled and welded shut, one upstream and one Downstream.The plug/wire just hanging there in the open..

So how is that possible without any CEL going off. Can I just go ahead and install them again, or has there been done some fancy tricks that I have to reverse before installing new o2 sensors.
Advise appreciated

 

When you cycle the key on engine off the CEL should illuminate. Does it?

 

Hi Cummins93, thanks for your interest.
yes, when I cycle the key all lights in instrument cluster lights up, including the CEL light, it stays on for a sec and then goes off, just as I suppose it should if everything is ok. But with no O2 sensors installed CEL light should stay illuminated….right,
I was thinking if the previous owner had done some trick to fouling the ECU…

Maybe I’m wrong but is seems like a mystery

 

Take a good picture of your ecu ID tag and post it up.

 

ECU Tag

Here you have it, one shut O2 sensor

 

I wonder if the previous owner installed a 2000 federal emissions ECU.

 

The part number on the ECU is for federal. That bung doesn't really look like it's in the right place for either Federal or California models though?

 

Hmm it a bit of a mystery, I’ll investigate some more and maybe just install the O2 sensor and se how it goes,

I’ll update the project when installed, thanks

 

What do you have for OBD testing? Can you monitor the O2 sensor signals? See what they're doing, a CA XJ with 4 sensors should look like:

 

What's the cylinder head? 0331? And the Part# of the block. That engine pipe doesn't look like a 2000 pipe, cause mine doesn't have that flange.

That said, see

 

Thanks, I only have one Cat and two wire for O2 sensor Upstream/Downstream, so it make sense if its a Federal 2000 model,
ill order a OBD2 reader today, any recommendations for a100 usd budget..

 

If you're short on coin then get an ELM 327 with software. I got mine for $3.95. They work.

 

My thought is that since there's no error codes the PO put in a gizmo that is sending in 2 fixed 0.1 - 1.0 DCV signals with Sensor 1>Sensor 2 (like S1 is 0.6V and S2 is 0.4V).

Or the ECU has been reflashed. Ask Cummins93 to see if that's even possible.

 

Flashing a 2000 cali to federal emissions should be possible but Ive not personally done it. If the single upstream sensor is in the collector for all 6 cylinders Id let it be.

 

$3.95...thats a price I understand..