Finding vacuum leaks
From Crankshaft Coalition Wiki
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==Overview== | ==Overview== | ||
An engine having a vacuum leak will tend to have an uneven, "hunting" idle speed. If the vacuum leak is sufficient, it may even run poorly under light throttle settings. | An engine having a vacuum leak will tend to have an uneven, "hunting" idle speed. If the vacuum leak is sufficient, it may even run poorly under light throttle settings. | ||
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Unless the vacuum leak is very large, the symptoms will disappear with higher engine speeds due to the relatively small amount of unmetered air entering the engine under those conditions. | Unless the vacuum leak is very large, the symptoms will disappear with higher engine speeds due to the relatively small amount of unmetered air entering the engine under those conditions. | ||
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Occasionally on engines that use the intake manifold to seal the lifter valley, you may experience a vacuum leak from the lifter valley area into the intake ports. This may be due to a bad gasket seal or because the intake manifold-to-cylinder head interface was not machined parallel (usually done to correct for [[milling cylinder heads]] and/or block). | Occasionally on engines that use the intake manifold to seal the lifter valley, you may experience a vacuum leak from the lifter valley area into the intake ports. This may be due to a bad gasket seal or because the intake manifold-to-cylinder head interface was not machined parallel (usually done to correct for [[milling cylinder heads]] and/or block). | ||
| − | No amount of propane or carburetor cleaner will find such leaks. The best way to insure there's no such problem is to use quality intake gaskets installed correctly, and to double check any machining before final assembly of the engine. | + | No amount of propane or carburetor cleaner will find such leaks. The best way to insure there's no such problem is to use quality intake gaskets installed correctly, and to double check any machining before final assembly of the engine. |
| + | These can be found by removing pcv and plugging pcv hole and attaching vac gauge to pcv inlet, then seeing if crankcase develops vacuum! GM 3.1, 3.4, and 3,8 engines have these problems often. | ||
==Resources== | ==Resources== | ||
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