Hi,

There is a larger thread about the issues with my car, but I will try to keep this short. I have had various idle issues with my XJR6 which I thought were resolved. I have changed failing coils, MAF, IACV, TPS, CPS, etc.

I had my car diagnosed by Jaguar (and the TPS adaptations reset), during this they found I had issues with my coolant temperature sensor (which previously I replaced), so I let them replace it - cheap job and the car then drove perfectly - not an issue at all!

Now a month on gremlins are back. The car stalls and idles badly until it warms up and goes closed loop. It did this before they replaced the coolant temperature sensor, my suspicions is the wiring to the sensor is faulty, can anyone give me the pointers how to diagnose this and fix any electrical issues down to the sensor?

I have tested the car before the sensor was replaced via my ODBII scanner and it showed crazy readings from the coolant temperature sensor at start up.

Thanks,
Nick

 

The sensor connects directly to the ECU. I would check the cleanliness of the contacts at the sensor and the ECU as a first step (corroded ECU connectors are common).

If all looks OK, then you could do a simple test of the continuity/resistance of the wires between the ECU pins and the sensor.

Then perhaps measure the voltage at the sensor pins and and simultaneously at the ECU from a cold start, up to normal op temp. If you don't have 2 meters do this in 2 separate runs from cold.

 

The 2 wire sensor values are om page 78

http://www.jagrepair.com/images/Trai...20-%202000.pdf

The 2 wires on the ECU connector are Red 14 and Red 31

Have you consider changing the thermostat as a cheap try ?


There is also the IAT sensor that should read the same at cold engine on sockets Red 1 and Red 31

I think the ECT and IAT sensor can be swapped .

The IAT has a lesser effect on the fuel trim or STFT

Look for broken tabs on the square sockets at the ECu and clean the sockets at the sensor

A dirty socket is higher resistance and on this thermistor sensor emulates a colder temp value / richer / open loop ECU mode

 

 

Correction on above

There is also the IAT sensor that should read the same at cold engine on sockets Red 1 and Red 30

 

 

 

In closed loop ECU mode after the ECT reches a certain temp the STFT should go from 8 % to 0.0 % as a target through all engine regimes

The ECU relearning should not accure unless a hard reset on both battery terminals or ......

A 25 STFT that goes to 0.0 on throttle up suggest a vacuum leak as it is scume replenishment superseded by stronger va

Motorcarman ( Bob ) had a suggestion of watching the coils in the dark for arcing to the valve cover plug well

O'Reilys ( not all so call fist ) has a Innova 4400 coil tester in the back room but you will have to go through the adapters to get the correct setup .

The power switch is on the back

Coil tester does not test for leaking coils , causing problems

 

You don't have to cut the bracket, just cut a tiny slot in the Jaguar special screw that hold the bracket to the ECU and then you can use a normal flat screwdriver to undo it. I've used an angle grinder to do it but probably easier with a dremel if you have one. BTW in my case ECU plug was fine, but I found a burnt out track inside the ECU and after fixing it my own car finally drives ok(no problems since August I think?)
Details here:
https://www.jaguarforums.com/forum/x...urgery-206839/

 

Hello Lady P and katar83,

I don't know if one can rename a forum thread they have started, but in this case it would be appropriate. I have been on two one hour plus journeys in my XKR6 over the last three days and logged the figures using my ODB2 scanner and phone - the coolant temperature sensor seems fine and so does the intake air temperature sensor. You can see them start at the same atmospheric temperature(ish) and then the coolant gets to circa 88 degrees C and the intake around 40ish C.

Idle seems OK-ish, some oscillation at idle, but nothing too extreme, more "missing a beat" here and there.

My key concern is the short term fuel trim (STFT). I have logged this over this extended period; after entering closed loop mode the STFT oscillates wildly from near on +25 and then back down to 0 and then into minus territory often late teens -16% and greater. The car seems totally unable to set a SFTF.

Driving it, it seems sluggish and petrol consumption remains bad.

I am pretty lost here and this has plagued my two years plus ownership. Apart from this the car is great - if I could only get it to drive properly.

Do you have any ideas what to investigate next?

Thanks,
nickdabs

 

I would try and run some tests on the O2 sensors.

Especially - power and ground or the sensor heaters, sensor signal ground, sensor signal from ECU. You can check all of these at the connector at the bulkhead (I suggest moving them up higher on the bulkhead for easier access while testing at least). Do these with sensors connected by back-probing.

Also, test the resistance of the sensor heaters with the sensor disconnected. It should be lowish ohms.

 

Hi Brendan and fellow forum members,

I think you're right, given I have a new MAF and have tested/cleaned/replaced the main sensors on the car apart from the o2 sensors this would be the next place to investigate.

I will update the forum as things develop.

Thanks,
Nick

 

Sometimes the O2 sensor connectors get hooked up wrong and yiu have to ptorhysically follow them

The connectors are the same and the wire colors are the same on the sensor side of the connectors

The difference is the 4th wire on the ECU side of the connector

Corrosion found in the connectors

Clean O2 sensor shielded wire grounds X 2 along the firewall upper edge , this prevents the super sensitive
signal from being corrupted

My engine was out of trim for a long time so removing and soaking the sensors in gasoline removed alot of carbon from the inside membrane

 

 

Hi Lady P and CountyJag,

Thanks for the good information. This is now beyond the scope of my DIY skills so I will get a mechanic on this one and share your thoughts and recommendations with him.

CountyJag the car has been checked for leaks before, but what you describe sounds worth revisiting as it might be more subtle.

Thanks
nickdabs

 

Nick, I assume you haven't actually checked the ECU yet? Have a look there, there are some topics here on the forum where XJR owners found completely corroded plugs/sockets there which caused all sorts of running issues, plus maybe you have a similar damage to my ECU, have a look in that topic mentioned above, inspecting is definitely something that you can do yourself

To go through things from this and last topic

1. You replaced MAF(I assume correct XJR MAF and not N/A one?), coils, plugs, coolant temp sensor, crankshaft position sensor, IATS, IACV. Are coils genuine ones or cheap chinese ones?
2. You did a TPS adaptation and I assume the garage also checked o2 sensor position.
3. Have they checked compression? Is it ok?
4. I assume it was checked for leaks and its ok.
5. I assume you've checked the vacuum lines that go into the intake and these are also fine.
6. OBD shows everything operational(sensor) and its just running rich.
7. Do all the o2 sensors go into closed loop mode and work?(does voltage change on them)
8. I assume it works similar on LPG which points to ignition and not fuelling?
9. Whats with the injectors? Have you inspected them/sent them for cleaning? If one is leaking(I saw plenty of these!) then its might be your issue.
10. I assume you haven't checked fuel pressure?
11. Is fuel filter filter and fuel pressure regulator new?
12. Please check the ECU, as per link in my previous post, if you're not able to do it, PM me, I might be able to check this for you.

Hope this helps and lets concentrate on these things for now!

Let us know how you get on!

 

Hi katar83,

As always thanks for your advice here are my answers:

All of the items listed have been replaced. I am using the World Car Parts MAF (part number LNA1620AA), currently I have the original coils in the car, but I also have a set of "Made in Japan" ones from SNG Barrett, there is not much difference in terms of performance between the two sets.
I only asked them (Jaguar) to do a TPS adaptation, they did uncover a faulty coolant sensor, but I am not sure what other tests they did if any.
Not that I am aware of, I will ask my usual mechanic to do so.
It has been checked for leaks and found to be OK.
I will ask the mechanic to specifically check this.
From my layman's ODB testing everything appears operational, besides strange short term fuel trim which widely oscilates between +25 to minus figures.
My ODB scanner reports car going into closed loop mode, but that is when the problems begin. I will ask the mechanic to check this.
On LPG the car behaves very very slightly worse.
Car has been terracleaned, but injectors have not been specifically inspected. If the injectors were faulty would the car not drive better on LPG? Either way I will get them checked.
Fuel pressure has not been checked.
Fuel filter was replaced the service prior to the last one. The fuel pressure regulator is the original one.
OK will do, need to get to work removing that bracket!

Many thanks,
Nick

 

Hi All,

A quick update, today my XJR has gone to the mechanic. It is still there at present.

So far he has:

1. Compression checked the car - all perfect.
2. Checked for air leaks including on exhaust manifolds - none found.
3. Checked vacuum lines that go into air intake - one was lose - correctly connecting it has not resolved the issue (which is disappointing as he thought he had cracked the problem).
4. He has checked the electronics concerning the o2 sensors all appears OK.
5. He has checked the earth/grounding points in case this upsets the ECU - everything perfect.
6. Diagnostics show strange fuel trims as found by me.

Next step is to replace o2 sensors which are on order. However he is saying the issue appears as a mis-fire and he is not sure the o2 sensors will resolve this. They have been in the car for 66K miles so changing them would not be inappropriate.

If they do not resolve things the only thing left is probably the ECU?

Any thoughts at this point would be much appreciated.

Thanks,
Nick

 

My eyes and brain is coming back somewhat but didn't read your earlier post

The main large engine ground at the frame surface cleaning from the starter bolt , From the bottom is easy , from the top not

Case ground on the ECU lower rear mounting bolt , Some valve grinding compound to chase out the car frame threads ?

I assume you got the 4 ground points on the upper side of the engine bay

Evap system line leaks , Check the line on the very bottom of the intake Man that goes to the purge valve

Carbon canister rust through causing leak , seal with JB Weld

If you have a left only or left and right 2 carbon canister system consider replacing the rochestor valve if equipped . Cheap Delco part # X

Brake booster line leak at the top of the intake Man

visually check the coils for cracks indicating arcing in the wells , effects the DC power in the rest of the car and corrupts the engine regulation in weird ways

Pull the rubber sealing gaskets in the coil connectors as they swell from chemicals and prevent a good pin contact

The Papa indy 1 connector White / Pink wire as this is the power to all the coils

Have you seen Al/'s ELM 327 graph that shows his voltage regulator not maintaining a constant B + on RPM changes ?

The middle wire on the TPS has a smooth increase in voltage from 0.60 DC at idle stop and up as you twist the butterfly by hand , no bips on the meter . Do not adjust at this time . My connector lock clip was missing

My have alot of carbon inside the vent slots on the O2 sensors not allowing the membrane inside to read , Can be soaked overnight in gasoline As I got alot out

Missing the crush washers on the O2 sensors throwing their readings off by changing the reach depth . The crush washers can be obtained from a cheap 12 MM spark plug box

Editing through day