Rubber vac hose connects to hard line as it disappears into the top of the trans tunnel.

What function does that serve? Car is on low blocks now, and I can't crawl underneath to look

Thanks,
Doug

 

Based on your description, probably the vacuum line going to the manifold pressure sensor in the ECU in the trunk. Picture would help.

Jon

 

As Jon says, if it is connected to a spigot on the middle of the crosspipe that connects the two inlet manifolds, then it is the vac signal to the EC, which is part of th sensing the ECU uses to adjust the injector duration.

 

Ah, so. thanks. That explains why there is vacuum to a place i didn't think any vac control modules existed, it obviously wasn't the TH400 vac.modulator.

I am used to more modern ECUs where the MAP sensor iss on the manifold, itself. There are some advantages to a long vac line to the sensor, it does ease transitory MAP spikes and give a more integral signal to the sensor.

Doug