I have a rough idle on start and whole my smoke machine is out for another car I want to smoke test my vacuum system on my XKR 4.2 to see if I can rule that out.

Where is the best place to plug in the smoke tester on this engine?

 

You can unplug the vacuum pipe from the fuel rail pressure sensor and connect to that pipe. If you don't have secondary air injection, that same pipe has a free end at the top/front of the supercharger. You can pop off the check valve and plug into that free end.

Just remember to block off your air intakes.

 

Some of the leaks don't show up until there's some solid pressure on the vacuum envelope. My '07 is 15 years old, and I found slight leaks on nearly every Oring. An off the Amazon shelf Oring kit solved all the leaks.

I'd start with a good solid seal on the TB (I used a solid rubber plumbing seal), then after getting all the ones that need real pressure, you can block off the lower ends of the intake piping with lower pressure (gloves and such) and check the various hose clamps between the MAFs and the TB.

Also, better to get a Jag compatible code reader than shotgun it. Need LTFT to settle on 0% + or - to test whether you got all the leaks and vacuum codes don't trigger until a 20% variance.

 

How did you pressurize the system? I suppose my smoke machine would do it, if I left it on long enough

 

I have a rent-a-garage with pro air equipment. But, assuming that the engine doesn't have an actual hole in it, you should be able to use a home compressor through the smoke machine -- the $120 pancake type would do. It may take a while to pressurize, but there not that much volume in an engine in any case. I hooked up the smoke outlet to the vacuum brake line into the engine.