Been chasing a misfire for the past couple years. Finally bought a smoke machine to see if I could find anything. In retrospect I should have done this long ago.

Houston, we have a problem. Ignore my O2 sensor extension in the foreground. The smoke is shooting out from a missed weld in the PCV hard-line on the left and clinging to the piping and rising out all along where the plastic covers normally sit. Here are a few pics to show the the issue. I'm going to seal it with some high-temp RTV for now and see if things improve. It's not under pressure and just pulls make-up air into the crankcase from the intake ahead of the right-side throttle body. Maybe the other way 'round. Either way it should be low pressure.


Stream of smoke slipping out from a missed weld in the PCV make-up line. My phone camera can't catch it very well, but there it is.



This hard-line is mis-welded from the factory. Neat.

 

All sealed up. We'll see how it works out.

 

Good luck 🤞

 

I'm not sure why I thought this would be the "smoking gun," There was a huge amount of smoke from the smoke machine that could escape under pressure. This ended up being the evap line from the carbon cannister at the fuel tank to return fuel saturated vapors to the intake ahead of the throttle body. There's not nearly as much vacuum pulling in fresh air as there was pressure pushing out smoke. I'm sure that there is *some* small benefit to eliminating unmeasured air getting into the intake, but after plugging the hole it doesn't seem to be much different. I've still got a bit to do to repair a passenger side airbox that is cracked before I can get it out for a misfire relearn to really know if it made a real difference.

 

Do you think the fact that the airbox is cracked could trigger the misfire?

 

It's cracked on the dirty side, but maybe it's possible. Looks like the previous owner got into a minor collision that snapped off a mounting tab.. It has been epoxied back together and finally coming apart again. New airbox is on its way.