Performing Smoke Test on M20 Couple Questions

[dr.strangelove]

Ok so today i went ahead and performed a smoke test to hopefully find an intake leak. Got things going and luckily enough, no smoke from the intake gaskets, fuel injectors or any vacuum lines.

I did however notice quite a bit of smoke coming from around the Charcoal canister. Has anyone here performed this test? Is that ok for smoke to be coming out of this area? The car was not running... Should i cap the charcoal canister off?

If anyone can shine any light on this, i'd appreciate it.

[bimmerboy12]

is there a write-up on how to do this? I need to do it badly.

[jlevie]

Smoke from the cannister or its hoses means there's a leak. The most likely cause would a problem with one of the hoses.

[Mike]

Doesn't the canister have a filter on the bottom of it, venting to the atmosphere?

[jlevie]

I don't believe so. The purpose of the canister is to collect fumes from the tank., which are then fed into the intake manifold via the evap control valve. Having the canister open to the atmosphere would defeat the whole purpose of the evaporative control system, which is to prevent the release of hydrocarbons to the atmosphere.

[dr.strangelove]

ok i will check the respective hoses.

Does the valve that runs to the charcoal canister default to open when the car is not running? If it's not supposed to do that, maybe the charcoal bypass valve has gone bad underneath the throttle body?

Jlevie, do you think this would play a role in my LOW idle? I haven't found a leak anywhere else!

UPDATE: 11:46am

I checked my bypass valve, and the valve was not functioning properly. I have replaced it with a properly working one, and i will try to repeat the procedure. A friend and myself did the test, (before i knew about the bypass valve failure) and then proceeded to adjust the CO adjustment on the AFM.

Now that i have replaced the valve, i will once again do a smoke test, and hopefully readjust the CO screw since i think it may now be out of adjustment.

Jlevie, let me know if you have any further input on this matter, thanks!

[jlevie]

There was certainly a leak there, as evidenced by the smoke escaping. And that would affect operation of the engine and mean that you'll need to reset the CO adjustment in the AFM once the leak is eliminated.

As I recall, that valve opens at certainly points in a driving cycle (it is controlled by the DME).

[dr.strangelove]

Ok, will do! I will go ahead, perform another smoke test, and then also reset the AFM CO mixture once i get that all resolved!

Thanks so much!

[dr.strangelove]

I have been looking around Jlevie, and i cannot find anything regarding resetting the AFM CO mixture screw. Any direction would be much appreciated!

TIA!

[jlevie]

I think I saw the procedure in the Bentley manual, but it might have been when I was looking at the TIS. Adjustment of the bypass in the AFM requires monitoring the CO level in the exhaust and adjusting the bypass for a specific CO reading. But before doing that it is critical to make sure that there are no intake leaks and that the TPS, throttle stop are operable and correctly adjusted and that the ICV is properly maintaining the correct idle. Note that leaks at the dipstick o-rings, oil filler cap, or in the brake booster are "hidden" leaks that won't usually show up in a smoke test.

[dr.strangelove]

ok will check into that. Can one go by ear in the meantime? I know that i have a slight leak at one of the exhaust manifold to downpipe flanges, and other than that, no leaks.

Bentley only states richen or lean out the mixture. that's it!

i also found this.

"If I had to tweak the CO set screw using the O2 sensor, I would warm the car up real good. This will make the O2 sensor hot. Unplug the O2 sensor connector at some place where you can measure the sensor's voltage with a voltmeter. With the O2 sensor unplugged, every 20 seconds or less rev the car above 2000 rpm for 10 seconds or so, to re-heat the O2 sensor. Let the car idle and measure the O2 sensor voltage. It should be like 0.45V if the CO% is set right. If it's like 0.9V then the car is idling too lean and you need to turn the CO screw to enrichen the idle. Tweak the screw. Then raise the rpm to 2000 for a bit to re-heat the sensor. Keep tweaking on the screw at idle (with a hot O2 sensor) until you get the O2 sensor voltage at 0.45V (or close to it). This won't tell you what your CO% is but it will get your CO% as good as you can by using the O2 sensor."

and then i have also read that the screw depth is determined by the number stamped next to the hole in mm. Any feedback on that?

[jlevie]

ok will check into that. Can one go by ear in the meantime?

Not really...

I would not want to try to set the bypass screw via data from the O2 sensor. It is measuring the O2 content of the exhaust, not CO.

[dr.strangelove]

I will try to tack up this leak, and then try to get it on an analyzer.

thanks!

once again, any info on that screw depth dealie?

"screw depth is determined by the number stamped next to the hole. Number is to be measured in mm."

[jlevie]

I've not heard that, but that means little to nothing.