I would drive the car more before saying it’s not fixed. As you’re not getting any more codes, right?

Z

 

No fault codes are present. Below is a summary and video as I want to keep the thread alive until I find a fix.


Bought the car with coolant loss, head gasket issues, and oil burning. Fixed by skimming the heads (0.1mm), checking all measurements, and fitting new OEM gaskets throughout. Car still smoked on deceleration.

Tried:

• Venting PCV to air → still smoked
• Disconnecting supercharger bypass actuator → still smoked
• Piston soak → still smoked
• Compression, leak-down tests, and engine vacuum → are all spot on.

Finally took it to a JLR specialist. They dismantled the engine again, checked the block and rings (all within spec), refurbished the heads with new OEM jaguar valve stem seals, did a full valve job, and pressure tested everything. Car still smokes on deceleration.

Smoke is engine oil burning. Car has all its power and does not smoke on acceleration or on cold starts.

Thanks

 

It definitely looks like oil smoke rather than fuel or coolant. As all the rings, bores, seals appear to be good, something must be promoting the ingress of oil or oil fumes into the combustion chamber although you seemed to have checked everything. What about the EGR valve, if present? Does that look OK?

How much oil per 1000 miles is she actually burning?

Richard

 

10 w 40 is the answer

 

There is a relatively new product from Valvoline called Valvoline Repair & Restore. It is a complete 5W-30 engine oil package that is used in place of your regular engine oil. It is said to clean out engine contaminants, including piston ring carbon. There are some credible, objective reports on this product on YouTube.
I have run it through my 200,000 km 6.0 l LS truck engine and have seen substantial cleaning of the visible valvetrain components, and noticed significant reduction in oil consumption after the second 3,000 km cycle. YMMV

 

5w 30 was always the thinnest **** they could put in reduce emissions etc change it up to 10w40 mine never used a drop

 

Have you seen the 0W-8 that they are using in North America market cars in order to meet the ever more ridiculous EPA mileage requirements? The same Euro-market vehicles still spec 5W-30. And they are wondering why the US engines are dying left and right! 🤪

 

The problem is the oil pump uses so much power at idle it increases the fuel used and hence the emissions.. Some idiots like land rover /BMW ar fitting a idle bypass to reduce oil pressure at idle ..what fools

 

on decel you pull serious vacuum

valve guide or rings idk what to tell you

 

Agreed but no point changing oil stem seals if the valve stems are fuko...Thicker oil will help....remember the days of 20w50 ....

 

Ok, so you are burning oil on over run, so oil is it being sucked in past the gasket, rings or valves.

Gasket has been fixed.

How to tell between the other two, do you get a puff of smoke at start up, this would indicate it's getting past the valves.

So does it smoke just on overrun or overrun and startup?

Overrun only would indicate the rings.

 

Before trying 10w-40 or 20w-50 (gasp, cough, cough) try the highest viscosity recommendation in the owners manual: 0w-40 . Mobil 1 0w-40 FS is a very highly regarded full synthetic oil that may impact your oil consumption.


I’ve been using it for the entire 83.000 miles of my 2002 XKR ownership, with the car getting very close to 199,999.

No oil consumption.

Z

 

Thanks everyone for the replies.

Since the rings have been confirmed good and the heads fully refurbished with genuine Jaguar valve stem seals, I’m leaning toward another cause. I’ve also tried both 5W40 and 10W40 oil with the same results.

I hooked up a vacuum gauge today. Warm idle sits just above 18.5 inHg, but on overrun/deceleration it spikes close to 27 inHg. Right after that, when I get back on the throttle, I get a puff of smoke visible in the rear-view mirror.

As a test, I introduced a controlled vacuum leak during decel. The smoke was either greatly reduced or gone altogether—hard to be 100% sure without someone behind me, but I couldn’t see any in the mirror. I repeated this multiple times, both downhill and at higher speeds, and saw the same results.

This leads me to think excessive vacuum on deceleration is pulling oil in from somewhere.

Could this be related to the throttle body valve closing too much and creating that high vacuum? If so, how can I test for this? Also, does anyone know the typical vacuum readings for the 4.2 XKR?

Idle vacuum reading

Controlled vacuum leak

 

Were the valves stems determined to have the correct clearance in the guides?

Richard

 

those vacuum spikes are normal.

 

The heads have already been off twice—this last time at a JLR specialist. They pressure-tested and found no issues, but still refurbed them and fitted brand-new OEM Jaguar valve stem seals. So I’m fairly confident it’s not valve guides or seals.

I’m back to my theory of excessive vacuum on decel. I logged the throttle readings on a hot engine and noticed the absolute throttle position is only 1.57% at idle. That seems very low. Could this be the throttle closing too far and pulling oil past somewhere during deceleration.

Idle (Hot Engine)
Absolute throttle position = 1.57 %
MAF = 7g/s
MAP = 30kPa
Coolant temp = 94°C
Target throttle position = 0.68V
Intake air temp = 58°C
MAP (voltage) = 0.83V
Pedal demand sensor 1 = 4.16V
Pedal demand sensor 2 = 0.86V
Throttle motor current = 0.000A
Throttle relay motor = On
TPS track 1 = 2.71V
TPS track 2 (CPU 1) = 1.57V
TPS track 1 (CPU 1) = 0.67V

At 2000 RPM in park.
Absolute throttle position = 6.67 %
MAF = 14g/s
MAP sensor = 15kPa
Coolant temp = 93°C
Target throttle position = 0.84V
Intake air temp = 58°C
MAP sensor (voltage) = 0.84V
Pedal demand position sensor 1 (CPU 1) = 3.71V
Pedal demand position sensor 2 (CPU 1) = 1.21V
Throttle motor current = 0.000A
Throttle relay motor = On
TPS track 1 = 3.34V
TPS track 2 (CPU unit 1) = 1.70V
TPS track 1 (CPU unit 1) = 0.83V



From what I see, the throttle plate seems to be closing very far on idle (absolute TPS barely above 1.5%), which might be creating excessive vacuum during overrun/deceleration.

Could a throttle body reset or adaptation relearn raise this baseline angle slightly and reduce the vacuum spike, or do these numbers look normal to others who’ve logged their cars?

Thanks

 

I have to say that in 55 years of working on cars I have never heard of the issue of excessive vacuum on deceleration. Excessive crankcase pressure / vacuum is one thing but you would have to be talking about excessive vacuum in the combustion chamber and I struggle to envisage how that would arise.

Richard

 

I haven’t cracked it either, and this one has mechanics scratching their heads. The vacuum seems to be influencing the intake in a way that doesn’t add up. What I’d really like to confirm is whether my absolute throttle position is normal or actually too low.

The car shows negative fuel trims when no air leak is present at idle, but on the move the trims sit around zero. If I introduce a small controlled leak, the trims return to normal. That makes me think the engine is effectively choking for air during deceleration.

I’d really appreciate it if someone could share their logged absolute throttle position at idle on a fully warm engine so I have a reference point.
Thanks

 

I know you have the 4.2 , and it may be different in this regard than my 2002 XKR, but I doubt it : my
throttle position at a wam to hot engine idle is 1.0%

I don't see how your idle position could be construed as too low.

Z

 

Thanks everyone for the input. Based on what I’ve gathered, my reading of 1.57% absolute throttle at idle seems to be within the normal range. I’ll be taking the car back to the JLR specialist tomorrow to see what they come up with and will report back once I have their feedback.