Jeep Wrangler/YJ 1987-1995 Repair Guide

Crankcase Ventilation (CCV) System


See Figures 1 and 2

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Fig. Fig. 1: 2.5L engine CCV system

All 1991-95 Wranglers are equipped with a Crankcase Ventilation (CCV) system. The CCV system performs the same function as a conventional PCV system, but does not use a vacuum controlled valve.

On the 4.0L engines, a molded vacuum tube connects manifold vacuum to the top of the cylinder head (valve) cover at the dash panel end. The vacuum tube contains a fixed orifice of a calibrated size. It meters the amount of crankcase vapors drawn out of the engine.

On the 2.5L engines, a fitting on the driver's side of the cylinder head (valve) cover contains the metered orifice. It is connected to manifold vacuum.

A fresh air supply hose from the air cleaner is connected to to the front of the cylinder head cover on the 4.0L engines, and to the rear of the cover on the 2.5L engines.

When the engine is operating, fresh air enters the engine and mixes with crankcase vapors. Manifold vacuum draws the vapor/air mixture through the fixed orifice and into the intake manifold. The vapors are then consumed during combustion.

Because this system does not use a vacuum actuated valve (as the PCV system found on earlier years does), there are few components. Check any system hoses for cuts, breaks or other damage and replace, if necessary. The fixed orifice should require no periodic attention and should operate properly unless it becomes clogged by dirt, debris or excessively sludged oil.

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Fig. Fig. 2: CCV system used on 4.0L engines