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post #3 of (permalink) Old 10-06-1999, 09:24 PM
dorfs
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Join Date: Sep 1999
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Re: Hey dorfs!

1. There are two manifolds, upstream and downstream. The upstream "Air Injection Manifold" and check valve is used for fast warm ups of the oxygen sensor. The check valves are to prevent exhaust gas from flowing up through the system. If the check valves are bad, it will create an exhaust leak, and also allow heat to transfer up to the plastic hoses and switching valves causing melt down. If you replace the check valves on the upstream side, and allow air to enter all of the time, it will fool the oxygen sensor, and drive the carb to a full rich position. Capping this one will probably have no ill effects other than failing for the visuial part of the emission test.

On the downstream side, the one that goes into the catalyst, again, capping it will technically fall under the "tampering" law, and also create a visuial failure. By leaving this one open all of the time, it can create a back-firing condition under rapid deceleration. Under rapid deceleration, you have high manifold vacuum and rich mixtures. If fresh air were to hit this rich mixture, explosions will occur in the exhaust. On earlier G.M. cars, they used a Pusle Air Injection Reaction manifold, which was open all of the time, and used a vacuum controlled valve valve that shut off air under rapid deceleration.

2. You can "educated guess" the setting for your choke pull-off. First, make sure that your choke idle speed is set to specs. I'm not sure, but I think about 2000 rpm on the kicked step, which is the second to fastest step of the cam. Remove the air cleaner, and cap all of the vacuum lines. The next morning, when it is cold. Hit the throttle once to set the choke, it should be totally closed, and the choke idle cam should be on the kicked position. Now start the Jeep, and with your finger, move the choke plate leaner or richer, to maintain the fastest speed. This is about the proper position for the pull-off adjustment. From your drivability complaint, it sounds like you need to go leaner, which is a shorter rod length to the pull-off.

Another point to keep in mind, Some pull-offs seem to work by visuially looking at them, they do pull in, and will open the choke during mild cold starts. But if they have a pin-hole in them and bleed vacuum, they won't have enough power to open a choke plate with a lot of spring tension, during extreame cold.

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