88 4.0 low vacuum
02-05-2013, 12:41 PM
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Model: Cherokee
88 4.0 low vacuum
what else can cause a low vacuum besides a leak. its bouncing between 14 and 15 inches at 700 rpm. i checked every thing i can think of. new intake manifold gasket, all the hoses, egr is blocked off. seems to run good but seems to be searching alittle at a idle
02-05-2013, 03:19 PM
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Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
CRUISER’S VACUUM TEST FOR EXHAUST RESTRICTION
Your vacuum gauge should come with an instruction booklet outlining the procedure. Hook the vacuum gauge up to a source on the intake manifold. Start the engine and note the vacuum reading. Usually 17 to 21 inches of vacuum. Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle. Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading. If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.
Your vacuum gauge should come with an instruction booklet outlining the procedure. Hook the vacuum gauge up to a source on the intake manifold. Start the engine and note the vacuum reading. Usually 17 to 21 inches of vacuum. Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle. Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading. If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.
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