High mileage 4x4, 7.4L 4door model: Hoses connected to emission control system have gone bad - one hose appears to be connected to a stem coming off the engine which is blowing hot "air". What are these hoses and is there a certain spec for the one carrying the hot "air" ?

High mileage 4x4, 7.4L 4door model: Hoses connected to emission control system have gone bad - one hose appears to be connected to a stem coming off the engine which is blowing hot "air". What are these hoses and is there a certain spec for the one carrying the hot "air" ?

You will have to be more specific...
Is this hose about 1/2" to 5/8" around? or a 5/16" vacum line.
Typically vacum lines will only have vacum, not blow air.

Where exactly is the hose coming from? If you can't describe, then post some pics for us. Many free websites such as Flickr will host your photos and you can paste the link to them in this thread.

The only hose I can think of coming off the engins blowing "air" would be a crankcase vent tube coming from either valve cover. Not familiar with the 7.4L, but one or both covers could have these tubes and may have a PCV (positive crankcase ventilation) valve. These would be routed to the TBI to reintroduce the blowby gases back into the intake charge. These are to help reduce hydrocarbon emissions. Pics would help immensely in this case, but hope this is a start. Good luck!