One more thing...I missed this message.

Yes, the ECU absolutely does control the heater. It changes the voltage on it based on how hot the motor is, throttle position, and MAF data in order to keep the temperature within operating range.

 

What kind of gas are you using?
Are you running a fuel injector cleaner of any kind in the gas tank?

 

They heat the O2 sensor to get it up to temperature ASAP so it can provide "normalized" readings to the ECU. You would think living in an exhaust gas stream would get it hot quick enough but apparently not.

The heating element is basically a resistor. Run power through it and it heats up. The two wires on the sensor with the same color are usually for the heating element. Heating elements don't care what "direction" the electricity flows through them.

The heating element does not report temperature back to the ECU.

Your ohm meter should have a "COM" position and an OHM position (looks like a horseshoe) for the leads. Then turn the selector to OHM (Horseshoe). There may be several ranges you can select. Picture attached.

You can test the sensors on the bench (out of the car).

 

No visible mechanical damage.

They were sooty, but not oily. The problem is I drove the Disco for about a week with the CEL on and she was definitely running rich. So its the chicken or the egg.

I did pull the O2 sensor and let the "tip" soak in a jar of gasoline over night. Swirled it around and wiped down. Looked clean when I was done. Reinstalled it and nothing.........

My 04 did suffer from the "Disco Rumble" at idle. I had a local shop run fuel injector cleaner through the injectors and it did smooth it out.

 

Gotcha, thanks for this explanation.

FYI - this has been on ongoing issue the last several months. We don't put many miles on it, other than for my wife needing to get to work 5 miles a day, and the last couple of weeks we've let it sit.

The truck runs great, smooth and plenty of power. Quick background, this truck within the last 10 months has new: MAF, Bosch+4plugs, Magnecor8mm wires, all new gaskets & seals (except crank seals and oil pan gasket), alternator, battery, pulleys, belt, t/stat, upper rad hose, so...pretty much the normal Rover stuff! hah, that's depressing to type out. AND new cats and muffler.

So, the truck runs great, just VERY RICH and therefore even worse MPG than usually (around 8 or 9).

I've been afraid the running so rich would harm other things, are there any protective measures I should be taking because of the overfueling? Additives or cleaners, etc?

Also, at this point am I led to believe my most likely source of the problem is now the ECU? Which now that I know how this system works, makes perfect sense.

 

Hey Spike, if this was directed at me...
93 octane always and no injector cleaners or additives.
I have used a can of seafoam in the gas tank in the past, as well as 2 cans (seperate times) of BG 44K. I haven't put anything but premium into the tank for some time now.

 

Well, you're running around in open loop most of the time, so I'm not surprised. It doesn't explain the sensors going bad, because the heaters are supposed to burn that stuff off. They shouldn't be going bad, but I doubt you'll get much for MPG with nothing but short trips like that.

And....wait...new cats? WHY? Were they rusted through, or not running properly? Because the same kind of things (other than rust) that destroy cats destroy O2 sensors. The plot may have just thickened.

 

Yeah, I understand I will get worse MPG's when we use it on such short trips and the truck doesn't even get up to temp.

Reason for new cats, they disintegrated and I blew some chunks of the cats out of my exhaust pipe.(pics in thread "cats coming out my exhuast")
That's why I got the new muffler as well.

FYI - I have tested the ECT sensor and it checked out too. But I know I haven't checked some of the simple first things to check yet. I'm still learning WHAT I need to check out, and then HOW to check it.

 

OK, well......these things are related. Running very rich will destroy your cats that way.

You really need to get this sorted out our you'll be back to buying new cats again.

 

My experience with O2 sensors encountering problems have been associated with exhaust leaks. It sounds like you may have an intermittant electrical signal problem though. Maybe you should try to isolate which wire/wires or plug terminal are the problem areas and bypass the area and sample.