Vacume leak 91 caprice


Old 10-10-02, 08:18 PM
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Vacume leak 91 caprice

91 caprice 305 a/t 63k mi. Got this car a few months ago for cheep cause it didnt run well. The engine idles smooth has good power, cruises at low and high speeds well, but It lags on acceleration, stumbles around at 40 -55 mph, and performes week under hard throttle. Two mechenics and one trans shop said torque conv./trans. So I replace them. Still same problem. I have performed a compression test, new plugs, wires ,filters, set the timing,checked for fault codes, everything I can think of. Every thing points to a vacume leak disturbing the timing. Since I got it I there has been a hissing sound like a vacume leak comming from under the dash when you accelerate. When you turn the key/engine off you hear a loud hisssss like air escaping from somthing. So I tore the whole dash apart and found the source. Its a black hard plastic box about 6in by2in with a rounded top. It has a black vacume line from the engine going into one port on it and another pink line that comes from it and supplies vacume to the modules that control the HVAC ducts. What is this thing? Could this be the source of my problem? Do you think a vacume leak is my problem? Im stumped my local repair shop is stumped. Any help would be great thanks alot Dave B.
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Old 10-10-02, 09:06 PM
Join Date: Sep 2002
Location: Colorado
Posts: 431
Dave, it is probably the vacuum resevoir tank for the HVAC controls. It's there to store vacuum when the engine is accelerating or decelerating and is supposed to keep the vents and controls in the HVAC system from changing positons during accel/decel. I dont believe that this should have any type of bleeder valve on it and that it should be sealed. Try taking the hose off the intake manifold and plug the fitting and see if your engine runs better. Also check out your PCV valve and hoses for leaks or plugging. Have you done a fuel pressure test yet?
Old 10-10-02, 09:46 PM
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Thanks stevo2, at least I know what it is now. No I have not done a fuel pressure test yet. I assumed that if there was a problem there I would get a code reading (but you know the old expression about assuming).The pcv valves seem fine but i'll take another look at them. I will try plugging the line as you suggested and driving the car to see if this helps. This old boat is in excelent shape with power everything leather seats and all the bells and whistles I sure hope I can get her right.
Old 10-11-02, 03:53 AM
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Rectify the vacuum leak and tell us what you've got. Those shops should have caught it....

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