Posted by Peter Florance on January 11, 2001 at 21:17:45:
In Reply to: Spring notches and bypass air. posted by Collins on January 11, 2001 at 16:49:07:
The air flow meter measures the amount of air that is entering the engine and tells that to the ECU. The ecu controls the injectors to delivery the amount of fuel correct for the amount of air measured by the air flow meter (AFM).
Here's the problem: the entire engine is under vacuum from the intake mainifold. As is the brake booster. But the intake manifold is past the AFM, so any air that is sucked in through leaks is not 'measured' by the AFM and no additional fuel is provided for that air. So 'da car runs lean.
And the AFM bypass screw lets air from the air cleaner side 'bypass' the afm. It is in effect, a little control-able vacuum leak. Why? For ease of adjustment. The car is designed so when the screw is closed, the car runs slighty rich from the AFM signal. Then the screw can be opened up enough to provide the extra air to make it right. Gives you some room to adjust things.
With the screw all the way closed, it tells me you need some more fuel. So by loosening up the AFM, you'll get back to the point where you'll need to give it a little air and you can dial it in with the screw. Right now you can't cuz the screw is closed and you still need either more fuel or less air. And you can't get any less air than none. So it's more fuel.
As a matter of fact, open the screw 2 turns before adjusting the air flow meter.
Then you could loosen the spring just enough to have good idle with the screw open and fine adjust with the screw. I predict you'll need to loosen 3-10 teeth. Anymore than that, something else is wrong.
Did Carl verify the fuel pressure? You might want to make sure before you get too wild with tuning.
With the fuel regulator vacuum line removed and plugged, the pressure should be around 35psi. Connected at idle it should be around 28psi.
The car should be adjusted and tuned to run warm.
Then you can fix any cold run/start problems IMO.
But fixing the warm running stuff will probably fix or help and cold start issues.
If you're really bored, check out the FAQ page. I uploaded the L jet seminar that I gave at the First Fives Fest in 1999
Peter