Hi, hoping to draw on the knowledge in this forum. Just bought a XJ 351 Diesel 3.0 on a 2016 plate. My first January and I really love the car. Recently had a couple of issues. Had "reduced Power" alarm pop up. And got my local specialist to do a throttle body clean up. But now I have another issue that he found which is "P02899-77 Supercharger/Turbocharger Underboost"

I am really hoping this is not a major fault and maybe to do with connections either perforated or cracked etc for the Turbo. Anyone have any advice or experience with this. Many thanks
Steve H

 

DrQuad, based on your error, I would start wtih the obvious and check your air filter to make sure it is failry clean and not clogged with something. The next check I would say to do involves a cigar. What you are going to do is turn off the A/C-heat and let the car get cold (let it set overnight). You are then going to light the cigar and then start the car. You are then going to blow the smoke of the cigar into the engine bay. What you are looking for is the smoke to be moving through the engine bay slowly and then suddenly make a direction change and speed up. This is going to point you to a spot where one of your intake tubes has developed a leak and that is causing your underboost condition. You can do this check until the cooling fan comes on. Then you have to let the car cool down again as the fan is going to blow the smokek around all over the place and send you on wild goose chases.

The other variation of this is to get some tygon tubing (say 1/4" ID) and then put one end of say 6 feet of tubing near your ear (DO NOT let it be able to form a suction) and then you run the other end along the tubing. What you are looking for is a sucking sound to appear. Where the end of the tubing is is where your leak is. Using the tubing and a second person, you can rev the engine up to make a little bit of boost and run the tubing along the piping, listening for some air to be blowing. The tubing is going to really let you listen to places that you could never think about hearing.

From there, I would be looking back at your throttlebody. it is possible that the throttle body is not opening up as much as it should be and is therefore giving you the "lost boost" error. This seems to be a problem with the diesels as I recall. I do not do a lot with the diesel cars, but do pay attention to some of their issues.

Hopefully someone else a bit more knowledgeable can come by and help.

 

really appreciate the reply. I will see what I can do with the information you provided. One good thing from what you're saying its not the Turbo which is on its way out. Which is good news cost wise. Thanks Steve H

 

DrQuad, if you know the turbo is on its way out, that would explain everything that you are seeing. Turbos spin at very high RPMs and if you have a bearing or something that is starting to go, that can greatly affect the boost that can be created. The computer assumes that the turbo is funtioning normally. So, if it starts to ahve drag and not making as much boost as it normally does, that will throw codes. I would be more likely to say at this point it would be a turbo than a throttlebody. This is where I would do the intake check and make sure you do not have a leak somewhere, then be looking at the turbo. The turbo looks like it is in a fun spot to swap out. Not too bad if you can get the car up in the air. BUt, having the turbo down near the oil pan is an interesting place to put it.

 

The problem is this is mainly a US forum. The US did not get any Diesels so we have zero knowledge or experience with them.
BUT our UK friends mainly purchased Diesels so they have tons of information and solutions.
Good bunch of guys and I am sure your problem has come up before.
UK Jaguar Forum

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Check out my post at. :

https://www.jaguarforums.com/forum/x...1/#post2659557


Read it all first, then you can compare.