I have a 97 Expedition with a 5.4. It started running really rough the other day, and had a pretty loud hissing noise. Obviously a vacuum leak, which I found, but I'm a little stuck. The PCV hose goes around to the back of the manifold to a vacuum T. The PCV side is intact. The hose (or possibly plug) on the other side of the T is gone.

I've felt around back there, and crawled under the truck, but can't seem to find any hose hanging loose.

I plugged up the leak, and now the truck runs fine. The check engine light is still on, but maybe it just needs to be cleared.

I can't imagine they'd install a T without the other side going SOMEWHERE. Anyone know what this other side goes to?

 

Yea, there's not suppose to be a T there. There's suppose to be a 90 degree elbow plugging into the manifold. I've never seen a "T" back their.

The T was probably installed by someone who didn't have the correct replacement part and the vacuum line plug must have blew out at some point.

It could have been used as a test port for vacuum testing or over all engine condition testing which is achieved by tapping into the main vac somewhere.

The correct part looks like this -



NOTE: This may not be the correct part # for your vehicle.

Disconnect your battery for 15 minutes to erase the KeepAliveMemory (KAM) for the light to go out. - This reboots the computer and needs to be done every time you work on or modify your air metering components.

It may be a good idea to clean the MAF sensor before you do this - IF it hasn't been done in awhile. - Heres how you clean the MAF -

http://www.fordf150.net/howto/clean-...low-sensor.php

 

Thanks. Now that you mention it, the PVC hose appears to be patched (at the sweep) with some larger vacuum hose. Maybe someone DID put in a T because that's what they had on hand.

I'll take your advice and clean the MAF sensor and then disconnect the battery for a while.

By the way, I forgot to mention it's 4 wheel drive. I think that's vacuum controlled too. The AWD light comes on, but I haven't checked if it's actually engaging.

 

They sell a PCV kit @ the dealership - not sure how much.

Yea , the 4WD locks threw a solenoid on the firewall (behind the battery) - blue and pink vac lines to an actuator on the front axle.