Throttle body adjustment-- help me understand.

JoeP · February 24, 2013, 07:57:01 PM

I've read a lot about throttle body adjustment and know the steps, but help me understand what's going on here. I've reset the tps and synced the TBs. Now I'm setting the air-fuel ratio.
1) When I screw in (turn clockwise) the air bypass screws, am I enriching or leaning?
2) Will the same action (clockwise turn) increase or decrease the CO reading for that cylinder?
3) High idle with the fast idle lever fully disengaged represents a lean or rich situation?

Thanks!

Howie · February 24, 2013, 08:47:21 PM

What year and model?

JoeP · February 25, 2013, 05:15:29 AM

Quote from: howie on February 24, 2013, 08:47:21 PM
What year and model?

Sorry, 2006 749. Lambda sensors disabled.

Howie · February 25, 2013, 05:57:01 AM

CO is adjusted by trim with diagnostic software. Air bleeds bypass the throttle plates are used to balance CO at idle and set idle speed. In ls richer (less air), out leaner (more air) and, until too lean, will raise idle speed.

JoeP · February 25, 2013, 06:08:22 AM

Quote from: howie on February 25, 2013, 05:57:01 AM
CO is adjusted by trim with diagnostic software. Air bleeds bypass the throttle plates are used to balance CO at idle and set idle speed. In ls richer (less air), out leaner (more air) and, until too lean, will raise idle speed.

Thanks! So leaner means lower CO reading?

Howie · February 25, 2013, 10:31:57 AM

Yes.

JoeB · February 25, 2013, 06:28:08 PM

Be careful. Too lean will cause big problems.

Your best method is to use a gas analyzer on a dyno first, to see how the mixture is set.

It's better to have a few more ppm CO than it is to have melted pistons burned valves and sparkplugs.

JoeP · February 25, 2013, 07:14:12 PM

I set it up today. CO for both cylinders around 4.5%, idle speed right around 1250 rpm, but TBs are just slightly out of sync. The manual says to favor CO balance over TB sync so I should just leave it, right? FWIW, I'm using a Carbmate to sync and at the highest resolution (0.5 cm mercury), I'm one blip away from perfect. Can't seem to get CO balance and sync simultaneously. The procedure I used was

1) sync TBs with bypass screws closed.
2) open both screws an equal amount to get good idle speed.
3) connect CO reader to V cylinder and adjust trim to get good CO.
4) connect CO reader to H cylinder and adjust air bleed screw on H cylinder to get same CO as V cylinder.

It was during the last step that the TB sync started to drift slightly.

brad black · February 26, 2013, 12:16:37 AM

set to co, ignore sync.

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Throttle body adjustment-- help me understand.