Vaccuum routing on a MAF-upgraded '86

moosejaw · 03-08-2001, 02:03 AM

All air that goes into the motor should be measured by the air meter. To follow the air flow path for the PCV it goes:

1. From intake to PCV valve.
2. From PCV valve to crank case (now this air has to come from somewhere So..)
3. From fill tube fitting to T-Body connection, then..
4. to air meter.

At low total air flow #'s (ie. idling) the ratio of air let in by the PCV to the air coming in through the normal route is very close. Lets say 1:1. If you don't have the PCV air "measured" you would be missing half the air going in the motor. Therefore your motor would run lean or stumble or surge at idle.

At high load the amount coming in through the PCV becomes insignificant because the ratio becomes very lopsided.

So if the PCV air is not measured it acts just like a big vacuum leak at idle. Vacuum #'s won't change but it will affect mixture calculations like a vacuum leak does.

Gray87GT I would hook up the hose again and then reset all idle parameters. ( I believe there are other posts in the archive that can describe the proper idle set better than I can.) This should help the idle air valve get into its proper control band to stop closing all the way and making a surge with the tube hooked up.

Mike
------------------
Live near St.Louis?
Check out Mustang Muscle and Dyno in High Ridge, MO
Check out my ride.

[This message has been edited by moosejaw (edited 03-08-2001).]

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03-08-2001, 02:03 AM	#8
moosejaw Registered Member Join Date: Apr 1999 Location: St.Louis,MO Posts: 274	All air that goes into the motor should be measured by the air meter. To follow the air flow path for the PCV it goes: 1. From intake to PCV valve. 2. From PCV valve to crank case (now this air has to come from somewhere So..) 3. From fill tube fitting to T-Body connection, then.. 4. to air meter. At low total air flow #'s (ie. idling) the ratio of air let in by the PCV to the air coming in through the normal route is very close. Lets say 1:1. If you don't have the PCV air "measured" you would be missing half the air going in the motor. Therefore your motor would run lean or stumble or surge at idle. At high load the amount coming in through the PCV becomes insignificant because the ratio becomes very lopsided. So if the PCV air is not measured it acts just like a big vacuum leak at idle. Vacuum #'s won't change but it will affect mixture calculations like a vacuum leak does. Gray87GT I would hook up the hose again and then reset all idle parameters. ( I believe there are other posts in the archive that can describe the proper idle set better than I can.) This should help the idle air valve get into its proper control band to stop closing all the way and making a surge with the tube hooked up. Mike ------------------ Live near St.Louis? Check out Mustang Muscle and Dyno in High Ridge, MO Check out my ride. [This message has been edited by moosejaw (edited 03-08-2001).]