Thread: evap
View Single Post
Old 05-28-2012, 06:02 PM   #63 (permalink)
Master EcoModder
Join Date: Jul 2008
Location: Silly-Con Valley
Posts: 1,462
Thanks: 188
Thanked 253 Times in 191 Posts
Originally Posted by mwebb View Post
a missing vacuum line on a speed density system such as your s will NOT cause lean condition
A vacuum leak can cause a lean condition, depending on where in the system the leak is. Leaks right by the intake valve do not have as much of a chance to propagate back up to the manifold, and can cause a lean cylinder.

However, most vacuum lines will be hooking up to the manifold itself, so your point is right on the money.

O2 sensor feedback has a limited amount of "control authority". In general, it cannot change the base mixture so much as to prevent the engine from running, at the very least. So a very very lean condition will make the O2 circuit go to full enrichment, but it might not be enough.

Again, though, this is a "corner case" and is not that likely to be what is actually happening when a vacuum hose is disconnected. But it is possible.
  Reply With Quote