Hi all !

As requested, I have been further checking on the O2 sensors side.

First of all, it is not possible to perform and O2 sensor test with my OBD Tool (car is too old I believe).

I have been checking voltages on the harness side and resistance on the sensor.

I am a bit confused. Here is a diagram of the B sensor, but the result is exactly the same for the A one. I did the test with the ignition on (but engine not running)




What is surprising to me:
- the fact that there is a tension out of the red wire. I assume if it is the signal from the sensor, there should not be a tension ?
- the fact that nothing is in accordance with jaguar "electrc diagnosis manual": the white wire should go to the ground, and the 2 blue ones should be a 12V power supply.
- When I look on the sensor side, it looks like the heating element (the one between I measured the 6.5 resistance) is receiving two power sources !

what do you guys think ? I have no knowledge into this.

One more thing to precise:
- when I switch off the ignition, there is still a 0,07 volts tension on connector B, but not on connector A
- I have tried to run with the O2 sensors disconected and it is even worse.
- I have tried to swap both connectors but it sounded worse. How to be sure they are connected in the right way ?
- The garage man gave me the old sensors and the connetors and pins were the exact same.

Thanks a lot for the help
Julien

 

Julien

You will need to test voltages with the Senor plugged in to the harness to get meaningful readings - you will need needle type probes to back-probe the connector.

There are 2 wires for the O2 sensor heater, these can be ignored for the purposes of this testing. The Red wire with 4.7V is the one you really want to look at. With the sensor plugged in to the harness and the engine running this should fluctuate between 0.1 and 4.7v. This is signal to the ECU from the sensor.

The OBD system in the car is not too old to measure the voltage. I have tested on my car today (Registered in Oct 1994) to confirm with 5 different tools. Only one of them was not successful as it could not connect to the car.

The systems I was successful with were Jaguar IDS, AutoEnginuity, Gendan (this is a cheapish generic ELM327 tool), and Torque on my Tablet using a very cheap bluetooth interface. I have attached a few screen shots. (Interestingly, apart from the Jaguar tool, the others reported max volts at around 1.2 but still showed the high/low swing which is the key.


Jaguar IDS




AutoEngineuity



Gendan Engine Check

 

Hello b1mcp !

Thanks for the answer and the illustration. That is very instructive.

Here is a photo of my OBD tool and I am not sure I can read O2 sensors with it. Yours seems to be much more sophisticated. Is it a specific program that you loaded on your computer ?




Do you know if I can monitor O2 sensors signal with a multimeter ? At least that would give me an indication if there is a signal going out of the O2 sensor, or if it is only receiving a constant 4.7 volts ?

What do you think

Best regards

Julien

 

Julien

Yes you should be able to see something with a multimeter. As long as the senor is plugged in to the harness, back-probe the red wire and you should see the voltage move from 0.1 to 4.7 (roughly) every second. The constraints are
1. This is the voltage at the point on the circuit you are reading. Some damage or corrosion further down the circuit may mean that the ECU doesn't see the same thing (you could measure at the ECU connector to over come this - it would be worth looking at that connector anyway as it is a common source of corrosion)
2. A multimeter will react more slowly so you will only see high or low, nothing in between.

I do not expect you to see a constant 4.7v as this would indicate rich rather than lean. For your symptoms, if anything I'd expect to see permanent ground on that wire.

There's also a problem of cause and effect here. You might expect to see low volts if the mixture really is very very lean. But you should be able to induce rich (and therefore high volts) by revving the engine. This would help confirm that the O2 sensors are working or not.


On the subject of OBD tools there are lots of tools for your PC/Laptop/Tablet/Phone that can provide a better interface for further diagnostics.

The Gendan tool I used for above can be seen here (although this is a later version than mine)
https://www.gendan.co.uk/product_STN327.html

The tool I connect to my Android tablet/phone is one like this with the Torque App.
NEW! OBD2 ELM327 V2.1 Bluetooth Car Scanner Android Torque Auto Scan Tool OBD-II | eBay

(I have no affiliation to any of these)

 

Hi all,

As suggested by several of you, I have been checking the signal out od the O2 sensors, and I don't know what to think:

With the engine running, at normal temperature:
Out of the signal wire (the red and the blue) of the O2 sensors, there is a tension very close to 4.5 / 4.7 volts. Sometimes, but not regularly, it decreases to 2.5 volts but then very rapidy jumps to 4.5 volts. Only once in 5 minutes the tension briefly decreased to 0.9 volts.
I did these mesures with a voltmeter

With the engine off, and ignition of, there is a permanent tension of 4.7 volts out of the 2 signal wires, on the harness side.

So, what do you think ?
- The signal is shorted to the ground ? But why 4.7 volts and not 12 volts approximately ?
- The ECM is not dead ?
- An air leak that would fool the ECM ? If so, why would be there a permanent tension out of the signal wire on the harness side ?

Thanks in advance for your precious help !

Julien

 

Hi b1mcp,


Sorry for interrupting the thread but I've been looking at getting a scanner and this item below appears to be the same model of Bluetooth scanner you posted above.
OBD2 Obdii Bluetooth Auto CAR Diagnostic Scan Interface Scanner Tool FOR Android | eBay
Because they are so cheap (and I assume are copies out of China) I've assumed you only get what you pay for and they may not work very well. Can you confirm they pick up the Jag codes? Thanks

 

Your figures confused me until I realised I had made a mistake previously, so firstly I need to correct a previous statement I made which was
"I do not expect you to see a constant 4.7v as this would indicate rich rather than lean. For your symptoms, if anything I'd expect to see permanent ground on that wire."

This is wrong. I was getting confused with normal O2 sensors (Zirconia) which are high volts=rich.

On the X300, a Titania sensor is used. These do not generate their own voltage. They merely vary resistance in line with Oxygen content in exhaust.
Hence they need to be supplied with a reference voltage (4.7v from the ECU in our case). This voltage measured across the O2 sensor will vary as Oxygen content varies and the O2 sensor provides a varying resistance to ground and will therefore pull down the reference voltage or not. (Someone more able than me with electronics can probably explain this better).

So it is right that you see 4.7v without the engine running. It is supplied by the ECU. (BTW I checked on my car and I also have 4.7v permanently on that wire, even with the ignition off - so that is not a problem).

I see nothing to suggest any issues with your ECU.

Evidence so far suggests that the O2 sensors are working and they are reporting a true Lean condition. But you could do a couple more tests to try and confirm that.

Warm up the engine and then with your multimeter connected to an O2 sensor induce a Rich condition by introducing some "Easy-Start" into to the air flow (removing the air filter will make that easy). This should cause the engine to rev a little higher momentarily but should also cause the voltage on the O2 sensor to drop (Rich mixture). If this happens then we can be fully confident that the O2 sensors are behaving correctly and you truly have a Lean condition.


Although you have checked for air leaks, I would check again. I would actually block off all the ports on the manifold (to mitigate against leaks further down in systems e.g. brake servo). Check again for any splits in the tubing/bellows from the MAF to the throttle.

For interest, I experimented with my car today and took some screen shots of O2 voltages in while inducing rich and lean conditions. These may be of use for future reference to members.

Firstly, this is normal O2 sensor behaviour in a healthy engine, at idle on a hot engine.



Next, This is with induced Lean condition (vac hose pulled off)



Next, this is with induced Rich condition (squirt Easy Start in to Air Flow)




I hope this is of use. Keep us up to date.


PS @Marke, yes that adapter should work fine with your X300. As you say cheap as chips so don't expect Snap On quality and longevity.

 

julien:
I do hope you get yourself setup with a OBD scanner software that can make charts. Brendan is showing prints from a high end version (AutoEnginuity), but there are several software packages that can do the same for fuel trims and sensor voltages for less than $100. and can be tried free. I am forgetting the name of one I tried with good results that works with a $25. Chinese interface module. I will look up the name when I get a chance and reort back.

Now, as to your wiring diagram, I believe there is some confusion. Pleas check to see if one of the "blue" wires has a purple stripe. That is the sense supply lead and I BELIEVE the wire you have as "red" is the sense feedback lead. The colors for that lead should be different in each of sensor positions. Is that right?

Now, back to the codes. With all sensors connected, which codes are you now getting a short time after a reset?

Also, have cleaned your MAF sensor?

Are you sure you have adequately diagnosed the vacuum leak? Can yiou get access to a good smoke machine?

 

sparkenzap wrote
" Pleas check to see if one of the "blue" wires has a purple stripe. That is the sense supply lead and I BELIEVE the wire you have as "red" is the sense feedback lead. The colors for that lead should be different in each of sensor positions. Is that right?"

Ross, that's not strictly correct. The Blue/Purple wire is a ground to the sensor.

The Blue wire on Bank A, and Red on Bank B, has a Ref voltage from the ECU. That voltage is pulled to ground through the sensor which varies resistance with oxygen content. Therefore the ref voltage on that wire changes with the resistance to ground (high resistance = high voltage (4.7v ish), grounded = no voltage) and that's what the ECU is looking at.

 

Hmmmh! Boy that is different from my notes!. Not that I doubt you are correct, since I was confused by the voltage readings versus the OBD readings and that is why I made some notes, but that was many years ago and frankly I cannot remember. The diagrams just show a common connection and return to the ECU.!

Ok, well if that is the case, then as you point out, there is a constant current supply to each sense lead and the voltage on the sense lead varies with the Lambda Sensor resistance. Either way, I fully agree with your recommendation to read the voltages with an OBD scanner which can chart the voltages.

Also, the actual sensor voltages have much less information for diagnostics than reading the LTFT and STFT, since the sensors only read the current state and that is affected by what the ECU is doing- indicated by the trims.

 

Dear All,


Thanks for the answers and the help.

I have been investigating on the 02 sensor side and everything seems fine, according to b1mcp explainations. I still have a permanent 4.7volts output at the O2 sensors. I have also checked for grouds on the O2 sensor harness but everything is fine...

So I am a bit lost:
- Fuel pressure / injection side: everything is OK
- MAFS : OK
- O2 sensors : OK
- Ignition: a bit weak to my mind but OK

I think there is something fishy going on here...

I will start again from the begining, even redoing what the so-called "garage" did earlier this year.

I have ordered a compression test kit to check if everything is OK with the valves. That will be a starting point.

What do you guys think ?

I will keep you updated !

Best regards
Julien

 

Dear all,

Here are some news from the jaguar, not very good in the end ...

As discussed, I measured the engine compression:

The methodology I applied:

• Removed all ignition sparks
• removed fuel pump relay
• Started with cylinder No. 1 (closest to the radiator)
• cranked the engine until the compression gauge needle does not move (approximately 8/10 crankings)

Here are the results:

• Cyl. 1: 12 bar
• Cyl.2 10 bar in the first test, 5 in the second, 5 in the third (I did the test three times to be sure not to be mistaken)
• Cyl.3: 12 bar
• Cyl.4 11.5 bars
• Cyl.5: 12 bar (but I noticed that the needle stuck at 9 bars, before rising to 12)
• Cyl.6: 12 bar

So, I feel that there is a serious problem on the cylinder 2 (sticking valve?).

What do you think of the next steps ? I think I'm gonna have to remove the head because I do not think it is possible to unlock the valve ?

Will I have to redo the valve guides and change the stuck valve ? Or cleaning it is enough?

Thanks guys for the help !

Julien

 

Dear All,

Long time with no update ! I have been very busy taking the head of the jaguar appart.

As you can see in the previous post, the compression tests were rather bad, so I took a big breath and took the head appart. The main issue was probably concerning cylinder N°2, but the other ones were not that good too.

I have performed a sort of test to see what is the cause: bad valves or bad segmentation.

I put some gazoline within the head (in the compression chambers) to 0see if the gazoline was escaping. I waited almost 1 hour. Cylinder N°2 was almost empty. Cylinder N°1 and 3 were very low too. Gazoline level in cylinders 6, 5 and 4 had slightly decreased.

So what can I conlude ? All my valves need to be rebuilt ? I believe that no liquid shoud be esacping at all ?

On the other side, how can I get sure that the segments are OK ? Should I do the same test ?

Here are some pics of the engine

Thanks a lot for the help
Julien

 

That's not a test I have ever tried, but it does seem safe to conclude that you need a valve job.

 

Dear all,

I think the problem is more than a valve job...

Today, I put some gazoline in cylinder 2 (the faulty one, with the bad compression rate), cylinder 3, 4 and 5

Cylinder 2 was empty after 20 mn, cylinder 5 after 40 mn, anf the 2 last ones were still full after one hour...

So, I believe segmentation is dead on cylinder 2. That would ne the cause for the bad compression rate.

What do you guys think ?

Thanks à lot for the help !

Julien