Updating my story,

Recently found a shop who has some kind of device for old jaguars and they could plug in and maybe reprogram fuel trims.
Unfortunately they can do this only in 2 weeks.
Interesting that the local dealer doesn't have a soft for older than 2004 cars.

Another sad thing occurred, while trying to figure out with the fuel trims and manifolds , yesterday started another issue - short rattling chain noise after cold or hot startup. . So i guess something with the tensioner, although its a new type tensioner.

Meanwhile I'm planing to change all ignition coils and clean tha MAF with cleaner.
Hope it helps.

 

Not sure that's a serious problem (chain chatter), even with the new tensioners.

If you do a search, perhaps in the XJS section, you'll find that it does continue with even the new tensioners.

 

So after a while quick update follows.

Have been busy couple weeks, but managed to make some changes and thats what i discovered:

I changed all the ignition coils - result no big improvement ,maybe the engine got slightly smoother, rpm's got more stable at idle. In fuel trims no changes.

But one interesting thing happened when i decided to check the coolant temperature sensor ECTS - connected the obd scanner and disconnected the sensor. The readings from 86 Celsius degree got to -40C and somehow STFT went from 24,2%( as it was showing all the time) to 0%. How can this be, if ECU thinks its cold why then he leaves the mixture at 0%?

Connected again, from 0% came back to constant 24,2%, temperature shows 86 Celsius degree.

Another thing what i did - I shortened the connector with a wire, the temperature ECU obd scanner showed 156 Celsius degree. And again STFT from 24.2% went back to 0%.


So my question - why if the sensor is showing kind of right temperatures, but with it connected ecu enriches the mixture anyway? With disconnected or shortened goes back to 0%.
SO if the sensor would be faulty why is it showing right temperatures then?

Any thoughts guys?

 

Hi RB_jaguar,

For clarification so we can be on the same page with you, which temperature sensor were you testing? The Engine Coolant Temperature Sensor (ECTS) on top of the thermostat housing; or the Intake Air Temperature Sensor (IATS) on the air intake elbow; or the Exhaust Gas Recirculation Temperature Sensor (EGRTS) at the base of the Exhaust Gas Recirculation Valve (EGRV) elbow?

Also, are all the temperature readings in Celsius?

Thanks!

Don

 

Sorry,

Yes I was measuring the Coolant temperature sensor on top of thermostat housing ECTS.
Readings are in degrees Celsius.

 

STFT is not a measure of mixture.

It is a measure of how much more (+ figure) or how much less (- figure) fuel the ECU is adding or subtracting from it's base fueling map at that moment.

When the engine is cold the ECU will be in Open Loop mode (i.e. it will not be monitoring O2 sensors to get the information it needs to alter the fueling) so will not attempt to change the STFT.

I suspect the same would occur with your out of range 156 degrees.


For your issues I would be looking first for an air/vacuum leak on the intake side.

Have you monitored the O2 sensor voltage with your scan tool? That might help with diagnosis.

 

I think this makes very sense, when disconnected the sensor, the ECU goes to open loop. Thats why the STFT goes to 0.
And logically thinking the leak on the intake side should have affect to both banks equally.
My scan tool doesn't allow me to monitor 02 sensors voltage, when I enable this feature it fails data reading and stops working. So can't monitor this data.

So next week i'm bringing the car for a smoke test, to look for leaks. Maybe i'll find some.

Keep you guys updated.

 

Brought the car to the smoke test. it appeared to be air leaking near the throttle body with hose connection, also a small leak where brake vacuum hose connects to the manifold.
So i reassembled those connections, cleaned them. Cleaned the throttle body aswell.
Started the engine and to my big disappointment no big changes in STFT, scanner showes same data +24,2%.
There was slightly higher rpms at idle at first, but after short drive it went back to normal.

So im basically out of options, unless last one is to reset the fuel trims if it possible.

Any ideas ?

 

I think we should go back and check out O2 sensors - your original post said that you replaced those. Can you provide so more information...

- Confirm that you used genuine Titania sensors of the correct type with the correct plug on the end, not generic ones (and not Zirconia)

- Did you read the STFT before the O2 sensors were replaced? Was it the same as it is now?

- Confirm that the STFT is definitely +24 on both banks. Are you sure it isn't +24 on one bank and -24 on the other (although I think if this was the case it would not run smoothly).

- It would be helpful to get voltage readings from the O2 sensors. If your scanner can't do that (I thought they all could) then use a Digital Multimeter to measure voltages at the O2 sensor connector on the bulkhead or even better at the ECU.

At the connectors on the bulkhead you should see a variable voltage between 0.1v - 4.7v. For sensor A that is on the Blue wire and for sensor B on the Red wire. Note these colours refer to the wiring on the Loom side of the connector, not the sensor side.

Also confirm that there is a good ground on the Blue/Purple wire.

 

Hi guys.

- O 2 sensors were replaced related to this fuel consumption problem, i didn't tested the old ones , but the mechanic said they where acting slow. I replaced both new - Titania type, correct ones.

-Before changing O2 sensors i did not read the STFT readings, but consumption was high, so i suppose they were same.

- Both readings on both banks are completely the same +24,2. They even act completely together. For example when you suddenly press for short accelerator on idle they both go to 0% suddenly and then slowly rises back to 24,2( completely together, not separate or different speed, they act as a pair.)
Sometimes they go to 0 when i go down the hill and completely depress accelerator, but as soon i press back they rise back.

And it happens since the car is started, and the readings go high, and stay this way, regardless engine is cold or hot.

 

- Both readings on both banks are completely the same +24,2. They even act completely together. For example when you suddenly press for short accelerator on idle they both go to 0% suddenly and then slowly rises back to 24,2( completely together, not separate or different speed, they act as a pair.)


My conclusion from this would be one of two things

1 - Your scanner tool is faulty and providing the wrong information

2 - There is a fault on the wiring for the O2 sensors.


The sensors (at least the sensor signal) are independent all the way back to the ECU so should not act completely in parallel - (they do share a ground signal and heater circuit). I could understand a fault somewhere else could cause them to behave in the same way but not completely in sync.

Try disconnecting the sensors one at a time and observing the STFT readings to see what happens on each bank.


Also, (I'm not sure about this but will try and test my theory tomorrow) I would expect if you press the accelerator quickly that would cause an increase in fueling as the ECU attempts to enrich the mixture for quick acceleration.


Can you get hold of another scan tool to check readings, or even try your scan tool on another vehicle.

And check out the voltage readings on the sensors as per previous post.

 

Hello b1mcp,

Today I did everything you told me,
So i took another scan tool from my friend and it showed the readings of both lambdas.

But they look very unusual to me.

At B1 at idle or steady driving i get the readings 0,000V , 0,005V 0.020V 0.015V sometimes always 0.000V
B1 by heavy acceleration or driving up the long hill while driving i get 0.340V 0.250V 0.030V sometimes 0.450V


B2 idle or steady driving i get 0.000 V 0.025V 0.140V 0.030V sometimes it just always 0.000V
B2 by heavy acceleration or driving up the long hill while driving i get 0.460V 0.870V 0.567V 0.785V

When i deaccelerate both banks basicly drops to 0.015 and 0.000V
B2 always shows twice as much as B1

STFT always constant 24.2% on both banks regarding to voltage.

I did disconnect one of O2 sensor, scanner did nothing, its just was 0.000V. and STFT no changes 24.2%.

On park , at idle both banks usually are at 0.000V-0.005V

I tried to measure the voltage on the connector of lambdas, on idle red and blue wire on the second, were showing 5.4V.

Why tester shows 5.4- 5.6 Voltage but the scanner shows 0.000V, or i was maybe measuring wrong way.

Is there a tester measurement scaling problem or i misunderstand something.

Anyway both lambdas show some activity , but do they have to fluctuate between 0- 5 Volts? In my case the highest they reach is B2 0.8Volts.

As mentioned before they are Titania type correct thread and same size as original. Changed 3 months ago.
Sensor i bought is http://www.ebay.co.uk/itm/Lambda-Oxy...item4891532a03

 

OK. This is making my brain hurt.

It could be that the O2 sensors are working OK. If the ECU is adding 24.2% fuel then we would expect the fueling to be rich. That would give a low voltage signal from the O2 sensor - and that's what is being reported.

However, the ECU should deal with that by reducing the fueling. But it is still continues to add (as reported).

So I'm really struggling here to work out some logic of what might be happening. I'll need to drink a few more bottles of Stella and see if that helps.


In the mean time there are a few more tests you could do to collect more information that may help

- confirm your voltage measurements at the sensor connector (this should be a maximum of about 4.7v). The connector should not be disconnected and the measurements should be taken by backprobing the connector on the loom side while the engine is running and is hot . For Sensor A measure voltage between Blue and a good ground. For Sensor B measure between Red wire and a good ground.

- While observing the voltage of the O2 sensors on your scanner, pull off a vacuum pipe. This should cause a lean condition in the engine and the voltage should rise.

- Get some MAF sensor voltage readings. @Vee suggested what the readings should be at various RPMs in an earlier post.

- Check the ECU connectors. Remove the connectors and make sure they are perfectly clean and dry.

 

Thanks for a help b1mcp,

I will remeasure the voltage of the both O2 sensors, and mass air flow.

Today was driving the city all day with the new scanner connected, and can't understand the sensors.

I noticed when i very heavy accelerate , almost to kickdown, the STFT goes to 0% sometimes even -2%, but thats as long I push the pedal. As I release it and drive at normal cruising speed everything goes back to 24,2%.

But the O2 sensors do not change their voltage when STFT drops to 0%, they fluctuate as usual around 0,750V 0,500V at haevy acceleration.

My point is if i press heavy on gas, STFT reacts somehow and goes to 0% , that means mixture gets leaner and O2 sensor readings should then go higher, but they never go higher than 0,800 0,900 Volts. ( even the mixture got normal)

Another thing - based on what then STFT regulates itself if not O2 sensor readings? Throttle position maybe? Or am i missing something?

 

I believe the sensors that provide info to the ECU that dictates fueling is (in no particular order)
1. MAF
2. Coolant Temp Sensor
3. Downstream Oxygen sensors
4. TPS

 

Hi RB,

Following up on Vee's post, here's the fueling input diagram from the AJ16 Engine Management System Dealer Training manual. Most of the inputs are self-explanatory. The engine load signal comes from the MAFS/TPS, engine speed comes from the CKPS, etc.



Cheers,

Don

 

@RB - I've worked out what is going on with your readings from the scanner. It is a feature (fault???) of the tool.

I had some time to play today so I did some testing on my car just to confirm what I thought I knew about O2 Sensor Voltages and Fuel Trim for rich/lean etc. Got some interesting results as follows.

The X300 uses a Titania O2 Sensor which alters resistance to ground as mixture changes rich/lean. It provides a signal of high volts (about 4.7v) when Lean, and low volts when Rich (about 0.1v).

So I ran a test using Jaguar IDS to monitor voltages and induced a lean condition by pulling a vac hose off. The results were as expected as shown in this screen shot.




As I couldn't seem to find how to display STFT in IDS (anybody know that?) I fired up a low end ELM327 tool on my laptop and carried out the same test, plotting O2 Sensor voltage against STFT. This is where the surprise came as when the Lean condition was induced, the reported sensor voltage went low.

I know it wasn't low as I had a DMM connected directly to the O2 Senor and that was showing the correct high 4.7v. See the screen shot below showing low volts on the sensor and high STFT.




Suspecting either a dodgy interface or software I then repeated the test with another tool. This time a Bluetooth ELM327 device and Torque Pro on my phone. The results were the same with O2 Sensor voltage being reported low in a lean condition. The picture below shows the graph from Torque showing around 0 volts on the sensor and +24% STFT in Lean condition, alongside my DMM showing high 4.7v on the sensor connector.





So the conclusion from this is that the low end ELM327 tools are incorrectly reporting the O2 Senor voltage. Don't know why.



So what does this means then for RB's problem? Not sure.

I'm suspecting that the O2 senor is actually reporting high volts (and scanner reporting it as low) and the ECU is correctly responding with increase STFT. We need to see the voltages measured at the sensor connector to confirm this.


I can think of two reasons that my be the cause. First is that there really is a very Lean condition in the engine. Second could be that there is a faulty signal ground to the sensor, so it never gets pulled below the 4.7v Reference Voltage.


So more in depth measurements at the sensor connector to confirm expected values on the signal wire and the ground wire are required.

Let us know what you find.

 

Wow b1mcp,
this is a very interesting discovery, that you have made. Thank you very much for your help and time.

Interesting that according this discovery, the car runs as it should and everything appears tobe fine. Maybe the very high fuel consumption is related to winter time and short distance driving. Although i was suspecting that something is wrong because the fumes/smoke going from tailpipe was always very significant. I even hear water bubbling in the tailpipe , what was leading me to think that the car runs very rich.

Tomorrow i will have more free time to play with the tester. I will run some tests with the O2 sensor itself. The tool i was using was Launch creader V and launch Creader IV.

Could you explain please how to test in a right way the ground of the connector?
One wire of tester to ground wire and the second to body or somehow different? Also what tester settings of ground measuring should i use? I know it sounds stupid, but measuring ground is not my strongest part.

 

Hi RB

I don't think the above suggests that there is not a problem. STFT at 24 is a problem.

My assumption is that there isn't really a Lean condition. If you have fumes (petrol smell?) from the exhaust then it is running rich but the ECU thinks it is running Lean. To me, that points to a problem with the O2 sensors/wiring.


If the car was in my garage these are the tests I would do next.

Firstly, with Ignition on but engine not running.

1. Test O2 sensor signal reference voltage.

- DMM set to DC Volts
- Connect DMM black test lead to good ground, e.g. engine bolt.
- Test your ground connection by touching the red test lead to a good 12v source e.g. the power connector in the fuse box under the bonnet on both sides of the engine bay. Make sure you have a good 12v+ reading.
- Now connect the red test lead to the Signal wire on each sensor. You should see about 4.7v
- This should be done by back probing the connector with a needle type test lead


2. Test O2 Sensor Ground

- Leave the DMM as is
- Leave the Red test lead as is
- The Black test lead should now be moved from the "good ground" to connect to the Sensor Ground - i.e. the Blue/Purple Band wire on the connector
- The voltage reading should be the same, about 4.7v


3. Test O2 Sensor Ground again

- Change DMM to measure Resistance
- Leave Black test lead as is from Test 2
- Touch Red test lead to good ground
- Resistance should be very low (theoretically 0 ohms but a low number is fine).

I've attached a couple of images that may help. First is a picture of the sensors showing the actual wires. Second is a wiring diagram for the sensors.


NOTE: I have moved my sensor connectors from the very hard to reach original location so that they are now on the bulkhead and easy to get to when needed. You might find that a useful mod to do before carrying out the tests. There's a post somewhere on the forum about this.



My guess is that on your car test 1 will be fine, but test 2 and 3 will fail. If it does we're on the way to resolving the problem.

Also, don't forget to do the MAF voltages check just in case we're going down the wrong route here.

 

Today performed the test with digital multimeter.

I measured the red and blue wires with ignition on to good ground - Voltage was 5,8- 5.6V. (not 4.7V). ????

With engine running on idle also 5,8 Volts, with engine running o idle and vacuum hose of - also 5.6 5.8V

Tested the red/ blue wires to oxygen ground blue purple - it failed. No measurements.

Tested the resistance from sensor ground to good ground - also no connection.

Since one pin of my tester broke down, i was unable to measure the MAFs voltage. Ill do this when i fix it.

So 2 and 3 tests failed, what do you think about that b1mcp?