VACUUM LINE sources and functions?

[gaz]

Hello,

1) Where is the small vacuum line on the bottom of the Throttle Body supposed to source it's vacuum?

2) There is a vacuum line coming off the front vacuum fixture of the upper intake manifold (passenger side) that goes to the small sensor on the passenger side wall just aft of the starter solenoid, forward of the 3 main relays? Also, what is the function of the vacuum line coming of the back of the EGR valve that feeds the same sensor?

3) Is the MAF supposed to draw vacuum from the front manifold source fixture or it's rear source fixture?

 

[Dirtman]

#1 no idea

#2 that is the DPFE sensor, it measures the difference in flow for the EGR valve to tell it when to open/close.

#3 Maf sensors do not have a vacuum source. They only measure air flow going past the intake tube. So I'm not sure you have the correct sensor.

 

[gaz]

Thank you for the responses ..)

I just found where the (#1) small vacuum hose under the Throttle Body goes; it goes to the EVAP canister. I had it plugged into the rear upper intake manifold.

I am making the correction today and report any changes. It is currently running but a little rough. I only recently plugged it in there by mistake.

 

[RonD]

Yes, the connection on under side of throttle body is a vacuum SOURCE, since its on the front side of the throttle plate it has "ported vacuum", meaning its vacuum level goes UP when throttle opens, instead of DOWN like vacuum inside the intake, back side of throttle plate
It was used for many years for the EVAP system directly, it would suck gasoline fumes out of the gas tank while driving(ported vacuum high), when moving the gas in the tank sloshes around which causes more fumes in the tank

 

[bcschief]

Most if not all 2.9s had a MAP sensor Not a MAF sensor. MAP sensor line runs from the MAP sensor (by the starter relay/solenoid to the upper intake right side usually a 1/4 inch black hard line.