Even a Jeep couldn't have so many things fail at once. What's the culprit?

Dear Car Talk

Dear Car Talk | Dec 01, 1995

Dear Tom and Ray:

I have a 1986 Jeep Cherokee with a four-cylinder, 2.5 liter Jeep engine. Over the past year, my four wheel drive has started to engage only part way, the cruise control won't hold its speed (it drops slowly), and the dash vents shift up to the defrost vents whenever the engine is accelerated. Since all of these are vacuum-based systems, what do you think is happening? Am I looking at minor do-it-yourself repairs, or is this more complicated?

RAY: Boy, have we got good news for you, Bill. Even a Jeep engine couldn't have all that stuff wrong with it at the same time!

TOM: It's got to be a vacuum problem. All of these systems are powered by the natural vacuum of the engine--the vacuum that's created when the pistons go down. That vacuum is carried through hoses under the hood and is used to power various things, like the power brake booster, the cruise control, and vent doors in the heating and air conditioning system.

RAY: And my guess is that one of the hoses that carries that vacuum is cracked and leaking. And since this leak apparently sucks a lot (it's a big vacuum leak), the good news is, yes, you can look for it yourself.

TOM: If you open the hood with the engine running, you should be able to feel around the hoses that feed all of these systems and determine which one of them is cracked. The cracked hose will be hissing, and that hissing sound will change when you cover the crack with your hand. You should also be able to feel the suction. Once you've found the offending hose, you can replace it yourself.

RAY: Or, if you're feeling lazy, you can get your local mechanic to do the whole thing for you (including the feeling around part) for less than 50 bucks. Good luck, Bill.

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