Hi All,

Long-time no posting!

I hope everyone is staying fit and healthy during these strange times!

As I seem to have some excess time on my hands right now I decided to attempt to remedy a niggling very rough idle from cold with my 2000 Jaguar 308 XJR (Vin F00075). Initially I thought it was a coil pack failure and on checking I had the following DTM codes showing: P0300, P0307, P0308, P1316, U1135, U1260, U1261, U1263, and B1948.

Not exactly sure why the U&B codes were flagged or if they had any detrimental effect on the cars drivability, but I dismissed them as random codes.

As part of a process of elimination I cleared the codes down, carried out a hard reset (disconnect battery and shorting +ve to the chassis) and test drove for about 30miles. Next day, started engine which initially started fine but within a few seconds began to rough idle considerably as the RPM dropped. (I also noticed the supercharger sounded like a washing machine full of marbles but will address this potential issue separately as it disappears as the engine warms). By normal operating temperature the idle had smoothed out a little but still not as you would expect from a V8 or any other engine for that matter.

I hooked up the scanner again (Auto Enginuity Scan Tool with Jaguar Enhancement) and pulled the same three codes relating to misfiring P0300, P0307, P0308, P1316. All other codes had gone. I swapped coil packs 7 & 8 for 5 & 6, cleared the codes and drove a couple of miles. I repeated the scanner check and almost as expected P0300, P0305 AND P0307 flagged up but NOT P0306 as anticipated or P1316.

As a Belt & Braces approach, I replaced coil packs 5,6,7 and 8 with new OEM Denso ones and fitted new spark plugs all round thinking all would be sweet again. Wrong!! The same symptoms persisted (very rough cold idle getting slightly better as the engine warms up but by no means smooth).

After driving several miles another code check was made. I then had new codes P1316, P1646, P1647 and P1797, but nothing to pinpoint the evident misfiring and poor idle which I assumed to be dodgy coil packs.

As the Bank 1 O2 sensors are not too difficult to access on a RHD I removed them to carry out some bench testing and found that the upstream sensor had high resistance of 2Mohms the heater pins (1&2) and provided only a few millivolts across pins 3&4 when heated with a blow torch. The down-stream sensor had an open circuit across the heater and no voltage output on 3&4 with the blow torch test. As an additional test of the heaters I rigged up a fused test lead to a spare car battery and connected to terminals 1 & 2 and confirmed the heaters in both sensors were dead.

Throwing more money at this old cat I bought four new Denso Oxygen sensors (2 up & 2 down) but before fitting bench tested them as I had with the old ones. Heaters worked fine and all produced a voltage of between 0.9 and 0.98volts using the blow torch noting that the voltage increased and decreased very quickly once up to a high temperature. Happy with my new sensors and the proven failure of the old items I replaced all four at the same time.

The result has not been promising!! Still the engine runs like a bag of spanners in a tumble dryer and the latest DTM codes, albeit only two of them now are P0135 and P0155 of which both relate to up-stream O2 sensor heaters which I know are perfect.

I checked the voltage at the upstream O2 plugs with ignition On there was nothing between pins 1&2 or between pins 1 and ground, but there was 11.8V between pin 2 and ground. On the assumption I may have a damaged wiring loom I checked the wiring by totally disconnecting the ECM and connecting a temporary lead between a known ground and Pin numbers 01 and 02 of ECM plug No EM85. In doing so I had 12V at the O2 plug pins.

I then reconnected the ECM, cleared all codes, carried out a hard reset again and with the ignition on checked to see if there was any continuity between ground and pins 01 and 02 at ECM plug EM85. There was not! Both remained open circuit during the test.

I’ve since removed the ECM and opened up to see if there was any obvious signs of blown components or dry solder joints on the PCB and I have to say all looked very clean and tidy even after 20 Years service with no obvious sign of failure.

In addition to the above I’ve checked for vacuum leaks and I did find that the hose which runs from the low load breather to a T connector on the throttle body had cracked and was leaking close the TB. This has been replaced with a temporary hose but is not leaking and the low load breather orifice was cleaned out with a 2.5mm drill bit at the same time, but this has made no noticeable difference to the engine running. There appears to be no other air leaks that I can find. But I did witness that in removing the cam cover breather pipe while the engine was running made no noticeable difference to the engine speed or tone which surprised me somewhat as I thought that would result in a lean mix and cause the engine flutter.

I also cleaned the TB.

I think I’ve covered just about everything I can think of to test and check for the poor idle and misfire and replaced with new anything I believed to be the cause (accept maybe the MAF sensor) and am at a loss to find the correct remedy.

Incidentally, MPG is down to around 15mpg from an average of 22mpg! I assume this will be due to the ECM switching to default fuel maps thinking the O2 sensors have failed?

If any of you guys out there can offer any further advice and steer me in another direction, I’d be very grateful as I’m lost for ideas right now.

Thank you in advance of any advice given to a most frustrating issue with my XJR.

Cheers!

 

As I understand it your car's O2s will be wideband (aka linear) upstream but the older kind downstream - did you fit the right kinds?

Your faults suggest not.

Failing that, I suppose carry out the tests relating to the P0135/P0155 as in the Jaguar DTC info.

The MPG suggests it is coping as best it can with what it sees as useless O2 sensors. It will run very rich - gradually destroying the cats which is its preference over lean which can rapidly destroy the engine!

 

Hi JagV8,

Many thanks for your reply.
I have no clue how you can tell if a O2 sensor is 'Wide Band' or the 'Older Type'?

According to the packaging and the order acknowledgement I received the following O2 sensors were supplied and fitted:
Denso Part No: 8717613018743 Grey Plug (Jag Ref: LNE1684BB) – Upstream
Denso Part No: 8717613018736 Black Plug (Jag Ref: LNE1682BC) - Downstream

Maybe someone can confirm if I've fitted the correct sensors please.

On the basis I've fitted the correct replacement items in the correct holes my concern is that the ECM is not signalling initiation of heater circuits. I would assume that from a cold start terminals 01 and 02 of ECM plug EM85 should have continuity between these pins and ground (Earth / -Ve) and mine does not.

I would assume that the O2 heaters are switched off at a set operating temperature, presumably determined by the coolant temperature sensor? So it's possible I have a faulty temperature sensor, but the instrument cluster temp gauge appears to be working fine.

Also, using a multi-meter the O2 sensors are transmitting a voltage output varying between 0V and 0.97V when the throttle is blipped (tested at the O2 connectors). But when they are reconnected to the harness and the Scan-tool is hooked up and running in live monitoring there is zero activity being reported from any O2 sensor (voltage or fuel trim %). The Scan-tool shows the O2 sensors being 'open circuit'.

Given the above issues and the other spurious codes thrown up in relation to CAN-Bus errors suggests to me the ECM is malfunctioning? Does anyone agree or no if there are any tests to verify my prognosis?

Thank You!

 

The elec guide show wideband upstreams (they're sensed via current, not voltage, and it's a tiny amount). No idea about part #s for your car.

I don't know that it does switch off the heaters but if it does it may well not do it the way you mention.

I expect it senses the heater ohms (or current) to detect they're not right so it's the heater circuit not just the O2 which is suspect, though the O2 is what you've changed so perhaps the most likely - I hope you've checked fuses/relays involved.

 

As described above. Front upstream sensors are 4 wire wideband sensors. Not even close similiar that are after cats. After cat sensors heater is fully on at startup when engine is running. After signal voltage is rised above certan point, ecu turns heater to low power. It is possible due PWM. Front sensors completely different here. Front ones are continually heated to maintain steady temperature inside the sensor. Sensor alters down the signal bias voltage what is fed to the sensor according left over air in exhaust gases.

Front sensor heater circuit resistance is around 1-2ohms. So anything else is wrong. After cat sensor heater circuit resistance is usually around 10 ohms.