The gaps in those plugs look huge!

Thanks for the updates - sounds like you're making progress!

Cheers,

Don

 

The 4 O2 sensors, after the fuel filter, got rid of 171, 174, & R P from the factor in my case. The air filter, & some O'rings,were already changed, as well as the M A F sensor, after cleaning the old one.My only remaining code is P O 101, looks like an intake manifold gasket, may may be the last remaining issue for me.

 

Yeh, on second thought, it appears that I was over-reacting to the problem. Normal maintenance plus scheduled replacement of consumable parts like the O2 sensors might have prevented or sorted the codes. It is just that the codes sometimes look worrying and there are far too many possibilities. Will remember that DTCs are not the problems but symptoms of the underlying problem. Anyway, I hope this time it is indeed the O2 sensors. I'll see.

 

$300 to replace all four of mine. Upper's = $103 each, lowers =$47 each, + tax, at Autozone.Densos are stock,and are recommended

 

Very high-level explanation:

O2 sensors respond with a voltage. Typically they are biased at 500 mV, and the changes in the exhaust mixture swing the output from 0 to 1000 mV (of course this can vary by vehicle and design). This is interpreted by the PCM as a lean or rich mixture, which tunes the fuel trims. Fuel trim have Short Term and Long Term, measured in % of change to the injection pulse. You ideally want to see your LT fuel trim at 0% for both banks, and the STFT will bounce between -2% - 2% as the PCM does its mixture adjustment.

Your upstream O2 sensors should have a switching pattern, as the design of the PCM is to change between lean and rich in order to keep the engine at the 14.7 AFR. This means you want to see your upstream O2s switching voltage constantly around the bias voltage (you'd see it as a sine-wave like pattern on a graph). As the O2s age, they may switch, but not though a full range of voltages. This may be your issue.

And yes, the O2 sensors need to be hot to operate correctly. They have an internal heater that can go bad as well. This can cause issues on cold starts if they don't respond correctly and give bad info to the PCM.

The PCM will actually set a code if it doesn't see the O2 voltage switching as expected, but your may still be switching enough that the PCM can't figure out they are worn out. Hence looking at data is the key to correct diagnosis.

As an aside, downstream O2 sensors should not switch rapidly. These should only respond to long-term mixture changes coming out of the cat conveter. If the data for downstream starts showing rapid switching mimicking the upstream O2s, then your catalyst is shot. This will set the code for catalyst efficiency below threshold.

 

Don,
I should pay more attention. (V6 vs V8). I too saw huge gaping on the plugs in the picture, also huge variance. If I can see the difference with my eye at an angle, they are shot.

 

The spark gap is getting wider, but not too much - see picture.


Factory spec says the gap should be 1.3 - 1.45mm. However, the main problem with the plug is age. Looks like it came with the car and is 12 years' old. I can see deposit building around the centre electrode and a flat spot more like a mini-pothole on the inside of the earth electrode. It seems that the plugs are not the problem of the RP warning. Three out of six plugs were replaced a few days ago and the other three have to wait till my mechanic has time. Meanwhile the pattern of warning lights emerging remains the same. Yesterday, the car almost stalled when slowing down for a right angle turn after climbing a slope with gradient 1:6. The throttle seemed hesitating and I had to step on the gas carefully to hold the car and then turn slowly.

Hope it was just the O2 sensors which are by far the primary suspects as the source for conflicting fuel too lean/rich codes. The other suspects are the fuel pump or the TPS, but the throttle body was replaced only two years ago. I'll see if all new four O2 sensors and new plugs will sort the codes and stop engine hesitation returning.

 

Try the spark plugs first, the O2 sensors can get expensive, there are four of those rascals, on an XJ8. I used Densos as they are the brand that came with the car, and seems like any car can be finicky, with some of the cheaper parts out there.

 

Update:
(1) The other three spark plugs replaced (it was a pain to replace them as they are hidden under the intake manifolds);
(2) Coils and air leak checked (no issue)
(3) Engine temperature sensor cleaned
(4) Throttle cleaned
(5) Engine oil and filter changed
RP warnings continue to emerge intermittently, following previous pattern. Set of four O2 sensors and transmission sump pan-filter-gasket kit ordered. Will see if their eventual replacement would sort out the engine light and intermittent dash warnings.

 

Just a note. Myself and many members of the forum chased a fuel trim/fault code issue for a long time, too long. We finally were down to O2 sensors. Changed a lazy O2 sensor after much troubleshooting, and vacuum leak hunting. O2 sensor did the trick. It was lying to all the other systems. Good luck. Am waiting to hear what the solution is.

 

Update: Today, my mechanic replaced all four O2 sensors with OEM Denso, the transmission fluid and the sump pan-filter, and cleared all engine DTCs. Car was running well until, again, the engine light and dash warning "Restricted Performance" re-emerged (!!!), and the engine hesitated when accelerating uphill, after it was parked for two hours and leaving an underground parking lot.

I shall scan for codes again tomorrow morning but, it seems the recurring problem was not caused by the O2 sensors or the transmission. What could spark off conflicting fuel too lean/rich messages, and what could cause bouncing idling between 600 and 800 rpm for 10-15 seconds at first start of the day, before regaining normal idling at 800 rpm in the next 20 seconds? My educated guess is the engine temperature sensor, fuel pressure regulator and the ECU, in that order. Any thoughts?

 

So the engine light and Restricted Performance (RP) message re-appeared, again intermittently, after all four O2 sensors were replaced. Subsequent scan produced only two DTCs: P0172 and P0175, i.e. Fuel too rich both Bank 1 and 2.

The mechanic and I re-examine the car again, and found cracks and a big hole on the side box of the air intake tube (see pictures).



The hole is surrounded by brittle plastic pieces - looks like the plastic is degenerating and falling into pieces. Perhaps the cracks and the initial hole were too small to be noticed at the beginning.

So this was indeed the source of air leak. Strange that this led to the "Fuel too rich" dash warnings after changing the upstream and downstream O2 sensors. Perhaps the O2 sensors have produced more accurate O2 readings, but the air leak alone does not fully explain the other symptoms, i.e.
(1) bouncing idling and misfiring on first start of the day
(2) RP message emerging at warm start after parking
(3) car seemingly pulling back when the foot is off the gas pedal
(4) engine hesitates during slow acceleration from almost stand still position.

The mechanic believed that (1) and (2) may be temperature related; (3) and (4) are caused by the air leak, as the air box is supposed to act as an air bank to avoid abrupt deceleration once the foot is off the gas pedal. Sounds rational to me. We then remember that in one of the earlier scans test running the IDS with a VCM kit which I just got from Cambo, among other fuel too lean/rich DTCs, one was DTC P0117, i.e. Engine coolant temperature circuit low input.

So my next move is to order and replace the Engine Coolant Temperature (ECT) Sensor (XR832403) and the Air Intake Tube (XR849998).

 

Have you blocked off the hole and checked codes again? I would before making any other changes. That way you will know for sure how that big gaping hole is doing. I assume that the hole is after the maf (un-metered air). That would be one hell of a vacuum leak.

 

The hole and cracks are too large to mend, and it only take a few days to order new parts so I'll just replace and check again. In any case, the car has been running alright most of the time, no stalling or anything, just occasional hesitation. Other parts replaced earlier I would just regard as part of preventive maintenance

 

Update: The new air in-take hose arrived; the bad one was replaced - see the gigantic cave, plastic was brittle around the hole, falling off in pieces upon the touch.



Daily heat cycle in urban traffic and the use of environmental-friendly material have hastened the air-intake hose's failure.

All codes cleared and the car drove fine for half a hour. When hitting slow traffic idling started to drop, and became unstable at traffic lights, getting worse every minute, eventually atalled a few times despite attempts to hold the engine rev through the foot pedal. Was moving like in limp mode to a parking lot and stopped the car. DTCs said "Fuel too Rich" both banks, as before. Left the car idling and saw white smoke (confirmed to be just vapour) from the exhaust tip - this was inconsistent with the DTCs...., but then in another moment the smoke turned black. Called the mechanic and he quickly suggested the MAF sensor which must be failing badly thus misfeeding the ECU with inaccurate and cycling data.

The MAF sensor on the car was bought new from eBay UK, and is an OEM unit matching the original Denso sensor displaying such part numbers as 1X43-12B579-AB and MB1974000-3021. On the mechanic's advice I put the old Denso sensor back and the car quickly recovered. I remember the mechanic had cleaned the old sensor once and reinstalled it before, but as the DTCs "Fuel too Lean/Rich" DTCs still re-emerged after installing a new one, it got me started looking for other suspects - this is the original purpose of this thread.

So now a broken air hose and an almost toasted MAF sensor jointly explain the "Fuel to Lean/Rich" DTCs. The new sensor was confirmed a bad unit as after changing the in-take air hose the car turned worse at low revolution, and also hesitated a few times on harsh acceleration.

My next step is to replaced the old Denso MAF sensor with a new, genuine part. British Parts lists the new part as Denso DMA-0113 (about GBP92); according to the JEPC, Jaguar Parts Number is C2S2670, listed over GBP130 on Jaguar Classic Parts. There are some confusions on eBay and various suppliers sites, but I am sure C2S2670 also suits the X-Type 3.0 V6 that shares the same engine as X350 3.0 V6, although most US listing says otherwise.

I have also bought three temperature senors (air in-take temperature, engine coolant temperature, and cylinder block temperature) as spares just in case the problem recurs after replacing the MAF sensor.

Hope that the problem finally rests here. Lessons learned are:
(a) scanners are helpful only up to a point;
(b) use factory originals for all engine-management-related parts; and
(c) parts suppliers' information on the web is not always right.

 

Was there ever a resolution? My 05 4.2 S Type is suffering the same condition. Thanks.

 

The problem has not returned since replacing the air duct and a factory MAF. You might want to rule out any vacuum leak before spending on expensive parts like the MAF.

 

This could be completely unrelated and you may have already checked. But, I recently had a 2 month run of hard starting, no codes. There was a hint on SDD to check for an intake leak. I "knew" the intake wasn't leaking -- until I took off the elbow and found whatever this is barely hanging on and glued it back. Problem solved. Found this link looking for an image to post here. https://www.jaguarforums.com/forum/x...-p0174-112414/

Hope this helps.

 

That cylindrical piece attached to the intake pipe is a Helmholtz resonator, designed to help cancel out induction resonances. At the factory, it was attached to the main intake pipe via ultrasonic welding. It is very common for the welds to let go, creating a leak point for unmetered air and leading to lean codes. Here's the photo you linked to, courtesy of Lagonia:



It is usually possible to repair the separation with a good 2-part plastic-bonding epoxy or other suitable adhesive.

Cheers,

Don

 

Thanks, Don. I wasn't sure what it was for, but that's exactly what I did. I thought it might be some sort of catch can for the line coming out of the valve cover since it's just under it. Thought it might help the fella troubleshoot. And you were right to give attribution to post I referenced. I should have done so.

Cheers,
Dale