Thanks for the tip. When the O2 sensors are installed, are they suposed to go all the way in and be flush with the exhaust surface? When I fitted my new downpipe, my current O2 sensors wouldn't go all the way in. At least, I didn't want to force them in. At the moment they are sticking out a bit with some threads exposed.

If they are meant to go in all the way, how do I ease them in so as not to damage the threads on the exhaust?

 

Gotta take off

 

The sensors go all the way in...

I'm assuming you're just using these used sensors as a test? Sensors do not last forever. I'd hate for you to install O2 sensors that have a questionable lifespan....

 

Just a test, yes. If it gets through the MoT with the used sensors, I’ll swap them for new ones and sell the used ones on eBay or something.

If O2 sensors are supposed to be all the way in, I’ll have another go at tightening them up. Perhaps that’s partly why my mileage is so poor. Any tips to get them in without damaging the threads?

 

Yeah, a thread chaser or a tap could be a solution. That's assuming your threads are damaged. You would have to know the thread count to get the right chaser/tap. RockAuto claims its an M18 thread...

Checking with Amazon, they sell M18x1.5 thread chasers that claim they're made to fix oxygen sensor threads, so there's a good chance that'll work.

It could also be that someone used a substitute/alternate oxygen sensor and the threading or the head size is close, but not close enough.

 

I undid the sensors, added a little anti seize, and managed to get them to go all the way in. No change noticed on a short test drive.

CTS is reading correctly, thermostat seems fine as the top hose gets very hot. I’ve ordered new ones anyway. How to test CTS signal is reaching the ECU…

Interestingly my cooling fans almost never come on even when the car has been sat idling for ten minutes and is definitely fully warmed up. Does that suggest that the ECU believes the car is cooler than it is?

I’ve jumped the fans at the lower left corner of the radiator and they both come on at slow and fast in unison, so it’s not the fans themselves.

 

Possibly bad news discovered. At the rear of the fuel rail, near where the O2 sensor plugs are, I’ve found 4 naked wires. They look like they should be attached to something. Any idea what these might be?



General location.



Yellow, blue, brown, and red wire hanging out of the wiring loom.

These are right next to the wires coming up from the O2 sensors.

 

Those are the colors for the O2 sensor returns to the ECU

You only need the rear 2 sensors for British model

O2 sensors connectors plugged in ?

There was a mod to relocate the O2 sensor connectors referred to as the Lambia Mod

The fan temp switch connector jumping on the radiator confirms the fan relay control module as well

There is a TSB on the fans to be in low mode regardless of the coolant temp with the key in run position

without the TBS done your no fans points to the thermostat being too far open and you have a higher coolant flow rate through the radiator

Fortunately , the cooling system is robust capacity and this may be fooling that you should be in low fan mode

ECU / CTS test points coming up

 

So these naked wires are for the other two O2 sensors which were never fitted to UK cars? If so, that’s perfect.

The O2 sensors are connected at the two plugs between the engine and the firewall, and they seem to be wired in to the loom. They’re those two black wrapped cables just to the right of the 4 naked wires in my previous photo. They seem to have 3 blue wires and one other colour wire each, although it’s hard to make out in the dusk light.

Hopefully new thermostat means I’ll get fans back. Might also be a reason for the rich running if the engine is cool then? Although CTS resistance and voltage readings are still fine.

 

The CTS sensor wires are socket Red 14 and 31

You would have to jumper the CTS connector as should not be able to read through the sensor

Uk cars do not have fwd 2 O2 sensors as 2 connectors on the engine block right

To know if the 4 naked wires are the 4 O2 sensor return wires to the ECU are ECU connector socket

2 wires that do not match are probably the O2 sensors feed which is 1 ECU socket Red 8 ( Blue / Purple wire at the ECU connector )

Somewhere they have the terminology mixed in the paperwork as these sensors are feed a voltage and the sensor varies in resistance to the oxygen content to get a modified voltage return to the ECU




Green wire / Red - 6

Blue wire / Red - 16

Red wire / Red - 18

Brown wire / Red - 19

Since your hi way milage is Ok means ...........

To know if the fans mod was done ..............there is a jumper plug on the 2 wire freon pressure switch to start the fans in low mode on key on position

 

I assume my CTS signal is reaching the ECU, as the car won't start or runs rough when the sensor is disconnected. It should therefore be giving the ECU correct info, as the voltage and resistances have read correctly at both cool and hot. It'll be replaced anyway.

My OBD scanner just reads 'N/A' when looking at fuel trims, perhaps that's because the O2 signal isn't reaching the ECU? Or is that because the car is staying in open loop running?

Maybe these loose wires are for the O2 sensors' return signal. I hope not, I'm not good at wiring! I'm hesistant to try and work out what these four wires are supposed to be connected to in case I damage anything else while poking around the loom.

I'll try and disconnect the O2 sensor connectors and test for continuity from the connector to the ECU. Hopefully will update later.

Another strange thing, I tried locating the four topside ground points in the engine bay to give them a clean, and was only able to find the left firewall one near the wiper motor. I found the stud for the front right upper ground point next to the washer bottle fill point, but it didn't have any wires on it. Is that normal on a '95 car? According to the manual there should be some ground wires attached to it. Perhaps that's the ground for options I don't have, headlight wipers or something. As for the other two ground points, the right rear bulkhead and front lower left, I have no idea where those are. Couldn't see any evidence of them.

Plan at the moment is to replace the thermostat and CTS, and see if the car comes up to temperature differently (maybe the fans come on, and the OBD shows fuel trim readings, engine coolant temp readings). If not, I'll move on to testing the O2 sensors' voltage and resistance and check they're reaching the ECU, then replace those if no change. Finally, I'll tackle the mystery naked wires and see if those are important. Oh, and I'll check out the manifold cracks and check for exhaust leaks.

A question on that last point, will a leak downstream of the O2 sensors cause the emissions reading to be out? It wouldn't change the fuel/air mixture, but does it change the result at the exhaust probe? I have a slight blow at the donwpipe to catalytic converter joint. If that would explain my high CO or low Lambda emissions results in any way, I'll look at rejoining those two exhaust sections a bit better. Sorry for the rambling post, just thinking out loud!

 

When a sensor is disconnected the value received by the ECU is not in expected range so it can be rejected and not used ( or still used depending on the ECU )

Removing the CTS connector ( high resistance ) simulates cold coolant and open loop regulation

There is a time delay as the ECU switches between these 2 states back and forth

There are 4 main ground points under the hood and left and right mirror each side , one under the engine air filter

There are a couple of relays only used on the V - 12 along with some accessories like headlights washer on the right front

 

Leaks downstream of the oxygen sensors should be irrelevant to the car. Probably smelly and perhaps loud for you, but wouldn't affect engine performance.

I'm glad you're replacing the CTS. It's easy and will cross it off the list once and for all. Your OBD2 reader should be able to tell you what the ECU sees for coolant temperature?

Getting a N/A for fuel trims? That's not a good sign, but could be a problem with the OBD2 reader? You should be seeing a STFT 1 and STFT 2, as well as a LTFT 1 and a LTFT 2. (long/short term fuel trim) Are you getting a reading on any of those four?

Can your OBD2 reader read oxygen sensors? It should be able to.

 

No reading for engine coolant temp on OBD II. I assume it's the OBD scanner at fault rather than the ECU, as unplugging the sensor does change the engine's running condition. So a signal must be getting to the ECU for it to change when unplugged, whether it's correct or not is another matter. I assume a slightly better OBD scanner would be able to read this temperature.

Nothing for any of the fuel trims. No idea if the scanner can read these, it's only a cheap one. I'll check the specs of the model and see if it reveals any detail about its capabilities. If these are reading N/A but the scanner should able to read fuel trims, does that instead indicate that the ECU isn't receiving a signal from the O2 sensors?

If that's the case, I'll replace the sensors and see if the reading shows anything, that would at least confirm if it's the twisted wires by the sensor that have broken or if it's something between the connectors and the ECU. Maybe it is something to do with the four naked wires I have...

At the moment, all my scanner can tell me is engine RPM, vehicle speed, throttle position, and work load as a percentage. It has a long list of readings to choose from, but they all say N/A besides the few I've mentioned.

 

The scanner live data technology is a patent of a Canadian company that is stolen by some to make the cheap Chinese scanners

In doing so they either don't get the whole technical package and what's missing ( or even test the product ) is not able to overcome by the scanners manufacture or even their technical ability to do so , hence why they steal it

They put the product out and get their money and nothing is going to stop them or change , they even say their product will tell you your horsepower based on unrealistic perfect engineering assumptions and not the real world what in service condition of your motor or other variables of consideration like broke , yea that one tells horsepower so I will buy that one and they get their money

There are maybe 3 or 4 serial ( ones and zeros ) protocols that the different cars use through the years for the scanner to find the specific address to retrieve the sensor or ECU calculated values ( fuel trims )

I think there may be 2 different protocols on the X300 production years

There is the default notion that the device is defaulting to the wrong protocol

 

Just got home from work, waiting for car to cool before I tackle the coolant sensor and thermostat. Interestingly, after 30 minutes of mixed driving the expansion tank and the hoses leading to it are not hot, although the top radiator hose is. I don’t know if that indicates anything to do with a stuck thermostat or not, perhaps it’s just because I wasn’t sat in traffic for too long.

Anyway, I’m hoping it does mean the thermostat is bad. I will find out shortly!

 

Remember no large O - ring on the thermostat

You can clean / sand the copper crush washer on the single wire coolant temp sender for the instrument cluster , it needs a ground path

 

CTS and thermostat fitted. New CTS won’t fully tighten, and it also isn’t coming out now. Probably damaged the threads… that’s a problem for a few years from now.

Went for a 24 mile test drive across hilly terrain, average speed of 47mph but most was cruising at 60mph. MPG when I got home was 28.1 (UK MPG).

Considering it was 20.1 when I got home from work earlier this evening, and a good tank is around 22, this looks promising. Even my best motorway trips at 70 only get around 24MPG.

I’m going to hold off on fitting the O2 sensors for a few days to give it a proper run to see a more realistic average after some commutes to and from work. If all it was was the thermostat, I’d rather not tackle the awful O2 connectors just yet.

 

Keep an eye on the CTS to make sure you aren't leaking when pressurized....

 

I think it's time you invest in a better OBD2 reader.

A wireless ELM27 and smartphone with the right app is probably the best answer?

iCarSoft i930 is an option as well?