Leak-down Test Intricacies
 

Hopefully a specific question with a simple answer. The background: I just did a compression test on the N14 on my R56S and found that the readings in cylinders 1-4 were: 150, 100, 130, 130.

Next step is to do a leak-down test. I've done them before, but never on a car with a throttle-by-wire. So my question is this:

What do I need to remove on the intake side of things to be able to hear air possibly escaping through a bad intake valve?

On cable-actuated throttle bodies that I've done leak-down tests on, I just pull the intake boot, jam a screwdriver into the throttle plate, and you're off and running. I've read that manually moving the throttle plate in throttle-by-wire isn't a good idea.

If I remove the air filter, will I be able to hear air escaping through a partially-open throttle body if an intake valve is indeed bad?

Thanks in advance.

Test Results
 

Following up by post with results and another question.

The leak-down test came back at 4-6 psi of pressure loss in each cylinder. I was running 80 psi from the tank, and the pressure in the cylinders was 74 - 76 psi. Not too shabby.

However, I did hear air coming from the oil filler from every cylinder. Not a ton, but it definitely wasn't silent. That worried me a little bit, and I'm not sure if that's normal. I was confused because of the low level of pressure loss indicated on the dial.

It it normal to hear a little bit of air from the oil filler during a leak-down?

A slight aside - it took a significant amount of strength to hold the breaker bar steady on the crank. The air really wanted to spin the engine. I didn't expect this.

I did another compression test and now cylinder 2 is reading about 135psi - not sure why it read so low the last time I did the test.

Any comments or advice would be appreciated.

in the initial number you got, was the compression test dry or wet? or was it cold or warm?

what is the background story to prompt a compression test?

The initial compression test was a dry test on a cold engine. This recent test was a dry test on a cold engine, too, HOWEVER, I had run the car briefly right beforehand to move it into the garage. Could be that that lubricated the cylinder walls better than the first test.

The background story for the test is this:

I had been sitting in traffic on the highway a few weeks ago and noticed white or blue smoke from the exhaust in my rearview mirror every time I touched the throttle to inch forward. I was worried that I was burning oil (more than it usually consumes, anyway) so I did the compression and leak-down to see if my valve seals were bad, or my rings, or if I was losing oil to the cylinders through the head gasket.

FWIW, I haven't noticed any more smoke since then, and I've put several hundred miles on it.

It is good that smoke didnt come back. I think moving the car might've contributed to better number.
Now, depending on the mileage, there might be carbon build up on the valves and/or the PCV is letting more oil than supposed to. Also, a quick look at the stem seals might help further diagnose the "issue".

Yeah, that seems like a good next step. I just crested 130k miles, and I had done a walnut cleaning of the valves at 90k, so it might be time to get them shiny again anyway.

Any thoughts on hearing air coming from the valve cover during the leak down test?

If the air is passing through the rings, it is going to escape to the crank case which is open to the valve cover.

You could try flooding the cylinders with oil to block the air and redo the test. You need a straw like tube to suck the oil out when you're done.

But since you dont have smoke at the moment, i would move to the maintenance/cleaning portion of solving the problem.

To answer your original question, there is no harm at all in forcing an electronic throttle open when there is no power to it. Just unplug the connector and prop it open as you always would.