When performing a smoke test, is it necessary/preferable to have the throttle plate open? If so, with a "drive by wire" throttle body, how is this achieved?

 

A smoke test is to detect leaks in the vacuum system that should be an airtight component. I don't believe that your DBW throttle should enter into the equation.

 

Correct me if I'm wrong but I was under the impression that it is in the "circuit". A failed throttle body O-ring would allow unmetered air. When performing a smoke test, the air duct coming off the air box is disconnected and sealed off. That duct goes to the throttle body which, in turn, is mounted to the supercharger intake duct. That duct interfaces with the S/C by way of the infamous green gasket. While there are other routes that the smoke can take, I'm just asking if the closed throttle plate would tend to inhibit the flow.

 

IMO, the butterfly valve on the throttle body would not be a perfect seal to begin with. Here's a shot of many of the vacuum leak possibilities if it's a help.

 

I have exactly the same question so would like to keep this thread alive. There is a video showing a BMW owner putting the smoke hose through a rubber glove sealed around the air intake with the filter box removed. Presumably the TB comes after that intake tube. But there is no mention of whether the throttle body is open. Doesn't the TB have to be open, and if so, how is it done without damaging it?

Or, is there a better (easy) place to attach the smoke hose? There is another video (a MINI) showing the MAP sensor grey tube being used. Would that be better?

Thanks for any help.

 

I did my smoke test as follows and it seemed to work fine: I removed my aftermarket airbox leaving my silicone air intake tube attached. I put a rubber glove around the silicone tube (where the air filter would normally be) and fastened it tight with its worm hose clamp (jubilee clip).

I removed the MAP sensor on the driver's side of the valve cover. It's the one that sits on top of the grey tube that attaches to the supercharger inlet tube. I wrapped part of a rubber glove around the end of my smoke tube, stuck it in to the MAP sensor hole, trying to make it seal into the hole. That is where I injected the smoke.

I then started feeding in the smoke from my home made smoke jar. I could not use the air compressor I had on hand because of a missing part so I used my lungs. I'm not sure if I made sufficient pressure that way, but I was able to pressurize the whole air system to the point where the glove inflated a lot, like a balloon, and I watched for smoke. I was pleased to see no leak from the dreaded green gasket (hint: use the genuine MINI gasket, not the aftermarket one - they have different designs). Also no leaks from typical vacuum leak spots or from intercooler boots. Weirdly after a few minutes there was some slowly seeping smoke apparently from a spark plug hole. I am going to investigate that further and may post about it.

Good luck!