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Engine/CDR Valve/Testing:

I curious if my CDR valve needs replacement. Anyone know how to check? I have a positive pressure at the valve cover, as well as the outlet side (the side leading into the intake manifold) of the CDR valve. I do not have vacuum at the manifold, however. Is this normal. Is it time for a new CDR valve?

One of the simple methods used to test the CDR valve is to run a length of clear tubing from the engine oil dipstick tube down to a small bottle containing motor oil. At 1500-2000 rpm, the crankcase pressure should be negative (normal case, CDR valve operating correctly) and draw some oil up into the tubing. On the other hand, if the crankcase pressure is positive, bubbles will be blown in the oil bottle indicating that you have a bad CDR valve.

Hope this helps.

Mark L. Gaubatz
1995 Silver Hummer

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