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Canuck Tech
Canuck Tech, Auto Service Technician
Category: Car
Satisfied Customers: 536
Experience:  Red Seal Journeyman Technician, 20 Years experience
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Jaguar Vanden Plas: I have a 2005 Vanden Plas 4.2L 125K miles.

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I have a 2005 Vanden Plas 4.2L 125K miles. It still runs fine no noticeable loss of power. Has been using oil about 1qt in 1500 to 2000 miles. Suddenly started smoking bad and when taking off from light or stop sign smoke is so bad you can not see cars behind you. If you step on it while driving to pass or accelerate same thing more smoke than you can see through. I have checked and no oil in water and no water in oil. Checked plugs, 6 looked normal 1 had white deposits one looked a little oily. Another strange thing when I pulled the valve cover there was not the usual amount of oil over rockers and cam lobes, They looked like they had been wiped off and very little oil accumulated anywhere. This concerned me but this 1st Jag. Water level is normal. The smoke is light gray/blue not black. I suspected valve seals but didn't know if they were leaking it would produce that much smoke. It does smoke even when going at stead speed but not extreme like when accelerating.

Hi there - my educated guess is that there is a piston ring / cylinder issue. Faced with the same issue, I would be performing a compression test and a leak down test. Most shops will do the compression, no problem, but a leak down is a much more of a pain. I think you will find low compression on one or two cylinders. The oil consumption is high for a modern car. If the compression is low in a cylinder or two, then there is no need to do a leak down test. I would "leak" it if the compression test didn't show a bad cylinder.


I am also concerned about the lack of lube on the top end, which could point to a restricted oil supply passage.


Hate to say it, but I suspect the engine is faulty. I would be looking for a good used one. If you re-use components, have the fuel injectors tested for flow and spray pattern before putting them back into the new engine.


Given the oil consumption, it is possible that a P0420 trouble code (catalyst efficiency) might appear down the road. Might not, but I thought I would warn you.


Hope that info helps you decided upon a course of action. Best, Canuck


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Customer: replied 4 years ago.

I will do compression test and also today look at other head after getting valve cover off. Just hadn't got to it yet on that side. I checked code before starting and only had 301 300 308 and maybe another misfire. I did have two p0171 and p0174 no others. Just got car as gift? since it had problems so a used engine is still a good deal for the car. One other question how do you get fuel line disconnected. From regulator to fuel rod?

Customer: replied 4 years ago.

Is the XJ8 and Vanden Plas 4.2L engine same?


Is it easier to remove engine with tran attached?

I'm not going to speculate as to whether the engines are the same - quite often the block will be, but accessory mounting, fuel delivery, etc. probably are not. If you calling a recycler, for an engine, they should be able to tell you for 100% certain.


Beside the misfire codes, the P0171 and P0174 are fuel trim codes - they mean that the engine was adding fuel to the base calculation to compensate for a perceived lean condition.


I'm not quite sure where you are trying to disconnect the fuel line - is it a round, push together connector? There is a special plastic tool



Customer: replied 4 years ago.

Other side looks as dry as first side. Plus I an see visible wear on CAM lopes. Think I'll go with used engine. What about removal? With transmission attached? Thanks

Without transmission. The Air conditioning refrigerant will need to be recovered. Canuck