Intake Leak (Pressure) Test ?????

[vol96]

OK, my little pea brain has never understood how the intake leak test (aka pressure test)can ever work. I've read the vfaq(s) and many posts discussing and explaining the leak test but still dont understand.

My quandry is this. Isnt there always one or more intake valves at least partially open, and wouldnt this allow air into the cylinder and wont that air leak, at least slowly, past the rings....(even if only a little bit on a good motor).

If I'm all wrong please let me know as bluntly as you wish so I can get this nagging thought out of my mind.

If I'm right, and there is some slight leakage can someone quantify how slow the leak should be (I'm talking only about air getting past the rings). Or should the rings totally hold air up to a certain pressure.



Thanks,
Befuddled Joe

 

[ADrewzki]

No. You're right. Once you pressurize, it's not going to hold that pressure indefinitely. It'll all leak out somewhere along the line. The point of it is to find the larger leaks in your system.

 

[vol96]

Adrew- Thanks for the reply.

I finally got my pvc cap/air coupler pressurizing adapter working properly and have found a couple of leaks. The biggest is a tear in the turbo to IC hose.....guess I'll be calling the stealer tomorrow unless someone can suggest an alternative.

Also found smaller leaks around the IAC and the TPS. My plan is to remove TB, spray some hi temp copper gasket sealer on the mating surfaces and test again.

This is all in an effort to find my rough idle problem.

I actually have 2 TSI's. Both are 95s. One auto (my son's....its the one I just pressure tested) and one 5spd (mine). Mine runs great and idles great. My son's runs good but idles very rough. I have swapped everything I can think of off my engine and onto his but it still idles rough and mine still idles great.

I have swapped:
plugs
plug wires
coil pack
power transistor
TB
BOV
Fuel rail
Injectors
FPR

I also blocked off the egr valve on both cars and both cars have the balance shafts removed.

Still mine idles great and his idles rough.