XJ XJ8 / XJR ( X308 ) 1997 - 2003

Video: possible vaccum leak?

Old 04-27-2019, 12:30 PM
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Default Video: possible vaccum leak?

Need advice on whether I've got a vacuum leak here:

When I blip the throttle, there's a sharp gasp of air before the engine revs normally.
It sounds like it's coming from underneath the inlet manifold.
It doesn't seem normal to me, but can anyone confirm / deny my suspicions?

Sometimes I'm not getting a lot of power from a standing start, eg at a roundabout, so I'm thinking this might be the reason.
Seems to be running reasonably normally once moved off though.

Old 04-27-2019, 02:48 PM
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Definitely sounds like an intake leak, along with the video, your description of lack of power on acceleration kind of confirms that. You can try spraying some carb cleaner in that area(s) to try to locate it...should bog the motor down for a moment. Don't spray a lot, just a couple quick shots, wait a couple seconds and try another spot..especially beneficial if you have a directional tip. Watch a Youtube video if you have to be sure and don't use the propane method.
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chris-jag (04-27-2019)
Old 04-27-2019, 06:32 PM
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This exact matter has been discussed before, but it has never come to a conclusion.

My VDP also has it, but only if blipping the throttle as you do.
I never noticed any performance issues related to it, nor any strange readings in short- and long term fuel trims or the balance.

If it is a leak, I suspect it to be either a leak in the vacuum hose going under the manifold to the throttle body, or it is a small leak in the manifold itself (I have seen a video of this on YouTube once).
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chris-jag (04-29-2019)
Old 04-28-2019, 06:19 AM
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I'd be suspecting one of these or anything related to the manifold.

Have a look at this short diagnosis.
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chris-jag (04-29-2019)
Old 04-29-2019, 10:48 AM
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Looks like I'll need to open her up then.
It's got over 200k miles on it so it's quite possible the manifold gaskets are brittle etc.
It has got worse since cleaning the air intake with throttle body cleaner.
Being a generous chap, I managed to get some of that stuff into the engine too.
Got a feeling I should have stayed in bed that day now!
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