I know my car has a vac leak somewhere. its louder with a hissing noise. when I first purchased it I remember thinking to myself is the car on? but now you can just hear air I'm not scared to do mechanic work ive done all maintenance myself. I just need tips on where to find the leak I'm hoping it should be a easy fix.




more information my cars gas mileage is noticeably garbage 16 mpg something like that. my car also recently threw out a p02420 code if I remember correctly which applied to the cats. I got it wiped and it will come back like a month later. my cars idle isn't ruff but it isn't crispy smooth as it was so I'm hoping the leak is the solvent to all. I think a slight loss of power is present. and the car is a 09 XF SC 4.2 @ 103000 miles now.


Appreciating all help

 

An old trick I've used is a spray bottle filled with water, start the engine and mist the engine in the area you think the vacuum leak is, the engine should stumble when you get close to, or spray into the leak. In addition, you may have to wiggle some vacuum lines to find it.

 

I swapped in a supercharger pulley this past week and my 1/8" vacuum lines were so brittle they fell apart when I touched them. Luckily the lines aren't anything special and I had some extra 1/8" vacuum line from my other car projects. It was easy to replace all the line vs. spending $50 on new lines from Jaguar.

The lines that appear to give most of the 4.2L supercharged people grief are:

-A 1/8" line that runs from a small nipple just above the rear of the supercharger to a diaphragm nearby. It's near the firewall, slightly off center toward the driver's side
-A 1/8" line that I believe connects to the back of the supercharger. It "Y's" off and one end plugs into another diaphragm and the other line appears to just have some odd plug on it. This is located back by the firewall but slightly off center toward the passenger side.
-Large tube running from the front passenger side of the valve cover to the rear of the engine. The rubber O-ring is on the ends is known to deteriorate.

 

>An old trick I've used is a spray bottle filled with water, start the engine and mist the engine

Another old "shade tree" trick is to use a can of starter fluid. Spray around and you WILL find the leak. The spray will get sucked into the engine and the engine WILL like it.

Plus, unlike water, any over-spray will evaporate immediately and leave no trace. You can be very liberal with the spray.
================================================== ===========
Understeer is when you hit the wall with the front of the car
Oversteer is when you hit the wall with the rear of the car
Horsepower is how fast you hit the wall, and
Torque is how far you take the wall with you

 

you guys have been great help I'm gonna give it another go and ill update

 

LOL, remember starting fluid is HIGHLY FLAMMABLE, while your being "very liberal with the spray" and will give you a rush if ya "huff it"..

 

Your vacuum leak is at the curve in the intake elbow to the sc from the throttle body where the brake booster vacuum line goes in. Theres a o ring in there, (well there was) and that is the most common and big source of vacuum leaks on that engine.

 

brutal you lost me with all the mechanic terms


I gave in another try just now no luck sprayed a lot of hoses tried to trace the sound to somewhere in the center front under where the intake tubes meet but also sounds a little to the left if you standing infront of the car

 

 

I found this picture on the internet is this the O ring you guys are reffering to?

 

https://www.jaguarforums.com/forum/s...-p0174-149418/


found this link to some info if anyone stumbles across this thread

 

I was having trouble once tracing a leak in miles of intercooler piping on another car. A local indy shop a few blocks away has a "smoke machine" that they hook up to the vacuum system, plug up the exhaust and intake and fill the whole system with a colored smoke. Pretty quickly the leak was traced, smoke pouring out from a defective clamp. Well worth the diagnostic fee. Never had any luck with any of the methods that depend on spraying and listening for changes in rpm or such. Seems the leak is always buried deep somewhere that I can't really get a concentration of flamable stuff right on it without feeling like I'm about to blow myself to kingdom come.

 

Keep in mind that is from the S-type R thread for their version of the 4.2L Supercharged motor. While the majority of the motor should be the same there are definitely differences which are not well known. I can tell you that I'm 100% sure the vacuum line connection next to that tube is is different on the 2009 XF 4.2L Supercharged. I don't have a rubber line running down to the aluminum like they show in that picture. I have a metal line that must come out of that hole which a rubber "Y" goes onto and then one line runs to that diaphragm and another goes to some sort of plug. You can see both ends in my previous picture above.

 

Well Brutal posted that and he is a factory Jaguar Tech. Glad to see you posting again Brutal.

I think all 4.2L SC engines have the same P/B port. Easy to look and check?

My best trouble shooting for vacuum leaks is the carb spray idea but at the same time I am monitoring the STFT with my OBD software. Those fuel trims will go nuts when you hit the spot and the engine won't miss a beat.

I never could find anything just using propane, carb cleaner. Engine never seemed to change at all. Never tried a pro level smoke machine but for home guys quick and cheap is the way to go. Everyone should have an ELM327 and an a phone app by now.
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Update- had the jaguar checked out almost got it smoke tested. took it to someone who knows jaguars a little more than me and had experience with s-types. anyway he noted "found crankcase vent valve leaking. need to replace crankcase vent valve." the part is $90 says that's coming from the dealer. here's a tip he applied pressure to the top center of the circle looking thing with his hand. the arrow is pointing to it in the picture and the noise changed volume. also noted that a smoke test would not have showed that spot to be faulty.


any tutorials on how to replace that part I like doing things myself saves $$ and ill look for a cheaper but OEM source any tips on that would help too.


Thanks again for any help.

 

that isn't a picture of my engine by the way I think its a xk engine

 

Air noise coming from that crank case vent valve is normal FYI. It's a common misconception on the S-type forums if you search. People think it's leaking and it isn't. I have no leak, car runs fine, no codes, and that same part you are pointing at makes noise and it does change sound when you push on it. I'd look into the lines by the throttle body as Brutal mentioned. That is the most common leak for the 4.2L SC motors.

I hope I'm wrong and the part fixes your problem. :/

 

Yes but did he confirm the leak by checking the fuel trims?

Very easy to monitor trims and spray carb cleaner at that area. Just because it sounds like it's making a noise does not mean anything.

I still think he is guessing and throwing parts at the problem. These are complicated engines and you have to use modern methods to troubleshoot them.

I still vote for the P/B vacuum elbow fitting and without taking the top of the engine apart you and your mechanic will have no idea if it's leaking or not.
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