Hi All,

I thought I would start a new thread - since this has been a long winded affair already.

FYI - 1997 (P Reg) XK8.
Cheap Ebay Bluetooth ODB Dongle and iPhone software. I've connected this to my Porsche and checked, it reads and performs well on that. It's also been reading some sensible date from the Jag, so I'm inclined to believe what it's saying, to a point!

Here's the story so far....

Previously, I had a dodgy battery, this has now been changed.
Also developed a fault in the ECU, it was throwing out all sorts of random error codes relating to either bank or both at the same time - spent today making sure that was the case, pulling it out and replacing the faulty components.

ECU and battery now seem to be working well again and I am back to where I was a few days ago....

So, now what I have is that the car's fuel economy is down the pan, the exhaust stinks - you can't stand behind it.

Hooking up the ECU and reading the data reveals the following.

Engine Temp reporting as expected
Air Temp reporting as expected
Revs reporting well
Ignition advance retard as expected
MAF sensor putting out sensible style data
Throttle position data seems right

STFT - pegged at about 14.5 both banks
LTFT - pegged at about 19.5 both banks
NO ERROR CODES, NOTHING, NO P1000 etc.

O2 Sensors - here's where things are interesting.

Fuel system is reporting all well and in Closed loop. Hence why, I think, there is no error code....

I have checked that the right O2 sensor is in the right plug etc....so that's all been verified thanks to images and wiring diagrams from you guys already.


O2 ODB reading is 0 - doesn't change for either bank. Am I right in thinking this should be average 450mV, and swing from 0.2 to 0.7mV? That's my understanding of the operation.

Heater coils on the O2 sensors seem to be ok....

When I hook up a DVM to the sensor and check the output the O2 sensor is reading about 150mV - but the ODB is 0... This is live comparison as I have back probed the sensor for the volt meter.

When I rev the engine to about 2500 rpm, it sees a wide open throttle condition, goes back to open loop and then the fuel trims respond as expected. The O2 sensor readings also move, but only a little. Back to idle and the fuel trims climb again. O2 sensor reporting as 0.

I also cannot see any ODB sensor listed for the down stream sensors - is this normal? Am I not able to monitor those?

As I understand, if the O2 sensor is reading low, it should back off those fuel trims and richen the mixture to make them switch and then when they go high, lean them off again etc etc - closed loop control - which is what it is saying it is in... But I am not seeing it as such.

I realise I am looking for a Vac leak, on idle - but to be honest, that is one hell of a leak to max out the trims, right? and I have made an inspection of the normal pipes, some small leaks to address but nothing like this.

Also the O2 sensor data is not corresponding with the trims - right?

This is also common to both banks.


Any one any ideas please - this is driving me nuts.....

thanks,

Matt.

 

You should be able to read all 02 sensors with obd 2

Sensor 1 is upstream (wide band) and uses Amps not Volts.
In your obd 2 app look for --
O2 sensor lambda wide range (current probe) (bank 1 sensor 1)
O2 sensor lambda wide range (current probe) (bank 2 sensor 1)
And set the number of decimals at 2.

Sensor 2 is downstream (narrow band) and uses Volts not Amps.
In your obd 2 app look for --
O2 voltage (bank 1 sensor 2)
O2 voltage (bank 2 sensor 2)
And set the number of decimals at 2.

If you set up a dashboard with the above Sae Pids you should be able to read all O2 sensors......

The upstream sensor should stay very close to 1.00 and move up and down from this very slightly..( eg 1.01...0.99...1.00 )
The downstream sensor has stoichiomrtric at 0.450 and should move up and down from this anywhere from 0.100 to o.900

THIS IS MY DASHBOARD SET UP.......

 

Also have a look in pending codes, (you may see something in there)

 

Your car most likely doesn't have them (mine doesn't).
My understanding is that they were only fitted to the early cars destined for the US market.

 

Ok, So here's the update from today's musing. I have looked and checked the wiring connections from the O2 sensor plugs back to the ECU. no problem, that checked out.
So While the O2 sensor was disconnected, I thought why not run the engine and have a look, no change, readings all still the same. no codes.

So, disconnected the other O2 sensor, start the engine, no change on the O2 monitors, but now I have a heater circuit failure code, as expected and the ECU is now telling me it can't be in closed loop control, as expected. But with one connected, it seems to be able to have closed loop control....strange....

I am now suspecting that both O2 sensors are defective and need replacement.

To recap, I started looking at these because the OBD is telling me that these are 0.00V to 0.02V always.
Fuel trims are ST 14.85 and LT 19.5 ALWAYS, except when the engine is revved and drops out of closed loop because of wide open throttle, the Short terms quickly go sensible and the LTs drop to suit. This means the ECU is able to trim fuel but not under feedback from the O2 sensors....right?

Why am I concerned about this despite no fault codes or warnings? Future MOTs and CAT damage, right?

Time for new O2 sensors? or does someone else think I am in the wrong direction on this?

thanks,

 

If the fuel trims drop at 2500 rpm that indicates a big air leak.

 

indeed. I thought that. I also thought that if it was that big, I'd be able to hear it even with my dodgy ears. Also I'd be able to find it easily with a can of spray etc, but nope. My understanding is that once you get up to revving the engine then the ECU goes open loop and hence the STFT drop back to sensible, if I hold the 2000 rpm or so then it goes back to closed loop and the fuel trims go back up. All this leads me to suspect O2 sensors, again, but I am having trouble believing both sides are bad and no fault codes. Mind you there are no fault codes when the sensors are unplugged other than the heater circuit ones. So that leads me to suspect a duff input is not captured, ie unresponsive just means the same as lean....driving the fuel trims up....???

Or am I wrong, please tell me...

thanks,

 

May help members if you post the actual fault codes you got and any codes in pending..
Can you confirm you only have the upstream o2 sensors and no downstream sensors fitted to your car ?

If jaguar only fitted upstream sensors to some early cars are they wide band ?
(Michaelh might know this)
The car should go to closed loop soon after startup, it will go to open loop under WOT but dont think this will happen in park as the limiter will kick in

 

As mentioned before, there are no codes, or pending codes....

It does switch from open loop to closed loop shortly after start up which I find strange.
My car does not have downstream sensors fitted. I can't see them anywhere or plugs for them and I have looked all over and checked against lots of reference images.
My car is a UK car and very early, so Jag info is they weren't fitted.

The sensors I have are heated 4 wire type - so I think this is Wideband - right?

Also, I have. no idea how old they are, they could be 24 years old now. The care is relatively low mileage - about 78K miles.

thanks,

 

Not been familiar with the early cars with only the upstream sensors i dont know if jaguar fitted the wide or narrow band sensor in these cars..
It dose make a difference which one is fitted as to the readings you are getting from your scan tool.
So you only have sensor 1 one each bank.
If narrow band then your readings from the scan tool suggest it is not working (giving correct numbers and switching high/low)
If wide band they may be ok and you need to check your scan tool is set in equivalence ratio (some scan tools may do this automatically)
Equivalence ratio sets stocimetric at 1.00
your scan tool may have stocimetric set at 0.00 and this is fine
Remember that wide band stays really close to stocimetric and only moves/switches in very small numbers.

Air leak would be more suspect than both o2 going bad.

 

Normally, they are about mid-way down on the body of the (vertical) cat converter, so not very much downstream at all. They are located on the back side of the cat near the firewall, horizontal, and point straight back. They are visible from the top, probably seen easier on the passenger side without the coolant tank in the way. They are also heated 4 wires, but narrow-band AFAIK.

Not sure reading the output will tell you much, focus on the trims instead. And yes, there are trims to the downstream sensors, too, at least on my '03.

Are you able to pull the status of the individual OBD monitors?

Do you have an Android device to use TorquePRO instead? Does not have to be an actual phone. A chromebook might also do as some are capable of running Android apps.

 

What you’re describing are the upstream sensors? These are the ones with the grey plugs and accessible from the top.

the down stream ones (if fitted) are below these and have black plugs.

at least from what I know.

after checking a lot - I don’t have downstream sensors fitted.

I also don’t have access to any kind of android device - this house is all max I’m afraid.

from my reading, narrow band or wide band, I should still see activity from them and not just zero.

from what I’ve read, The earlier ecus can happily drive the fuel trims out of whack with zero volts as it only sees that there is something. If the sensor is not present or not outputting at all, then it will throw codes.

that’s how I understand things.

checked the code reader and same software on my other car (Porsche) and all similar sensors read and display correctly.

 

I was describing the downstream sensors in the earlier post. The upstream sensor is more on the upper elbow where the cat meets the horizontal cast iron exhaust manifold. It is sort of right there. I have replaced both kinds. The upper sensor is removed from the top, with a fair access. The lower one is apparently reachable from inside the cabin by removing A/C drain plugs on the earlier car, but I had to drop the cat on mine.

Is the lower sensor threaded hole just plugged on yours?

 

If your upstream sensors are wide band and your scan tool is setting the equivalence ratio for stoichiometric at 0.00 you wont see much more switching than you are above, this dose not mean the sensors are not working as they should.

 

I can see the upstream ones as you describe from the top.

without taking the Cat off, which I’m not planning on doing, I can’t see if the hole is plugged or not present.

maybe I’ll know more when I get them out. I’ll post back.

I’ve ordered new ones. Whilst I have some documentation on the car, I don’t have any evidence to say that they’ve ever been changed. So new ones are going in now. I’ve also read that they can be lazy and push the fuel trims by giving low readings. If they’ve never been changed then they’re 24 years old now and 77k miles on them.

When I first got the car, I did have the engine terra cleaned and that threw an issue with the original throttle body. The throttle body was a recall on the car, which was also never done. The independent specialist I saw, shook his head about the terra clean and said it can mess up all sorts of things on these cars. So thanks to top gear for that!

Also when I got the car, it had no evidence that the timing chain tensioners had ever been looked at. So I just got those done soon after buying in. That was a lucky escape as the tensioners has failed and were already rubbing though the chains. So I caught that in time.

certainly interesting owning these cars.

 

My understanding is that all the upstream O2 sensors are wideband, and the downstreams (where fitted) are not.

Courtesy of XKRacer, here's a picture of some cats that, like mine, don't have the lower sensor. There is a blank moulded boss where the sensor would fit:



Torque is available for the iPhone, although I thought the latter could only connect via WiFi. Apple has got bluetooth sorted?

 

Interesting........
So what have you ordered ?
Air/Fuel Wide band sensor or o2 oxygen Narrow band sensor.
I believe both Wide/Narrow band sensors on the XK8/R are both heated.

 

A big (to the car) air leak is commonly not audible.

Squirting small amounts of a burnable substance such as propane will make the STFT(s) go wild briefly if you have and find a leak.

(You can perhaps grasp this if you think how little air goes in at idle and thus how little fuel, and then how tiny extra air disturbs things.)

This is IF there's a leak.

 

I’ve ordered upstream sensors as they’re the ones that are fitted in my car. The Downstreams aren’t fitted.

still need to confirm about leaks etc. I’ve been round it with some squinty stuff, but not found anything. I’m in the process of knocking up something for smoke testing.
it’s all a bit slow with deliveries etc at the moment.

 

Good look with getting this sorted,
The new upstream sensors should make a difference if you are running on the original 24 year old ones.
I still think your obd app is not set correctly to read the jaguar up stream sensors.
I could be wrong,
but i had trouble reading my up stream sensors and it took a lot of trial/error to find the correct Sae Pid to allow my obd app to read this sensor, Keep safe and keep us posted with your progress..