Annoying loud high pitch whine or whistle from engine compartment
08-25-2017 | 07:02 PM
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Junior Member
Joined: Apr 2013
Posts: 94
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From: Georgia
Year: 1998 , 1999
Model: Cherokee
Engine: Both 4.0 IL6
Annoying loud high pitch whine or whistle from engine compartment
BRAKE BOOSTER! So this is me sharing knowledge on what I figured out.
Ever since I bought this Cherokee back in January, I have been hearing an annoying loud, high pitch whistle or whine coming from the engine compartment that reminds you of the high pitch whine an old CRT television would make. It had progressively gotten louder. It was driving me crazy. I tightened the manifold bolts, no change. I cleaned the throttle body, changed the throttle body gasket, no change. I assumed my manifold gasket was bad, but I was not going to change it until I could afford a new header since it is such a P.I.T.A. to pull all that crap off to get to it. I also had intermittent hesitation issues that just wouldn't go away.
So about 4 days ago, I was stopping at a stop sign when all of a sudden I heard a loud CRACK! that sounded like a small fire cracker from under my feet. This was not a back fire or a pop. As soon as the crack was heard, my engine died, my brakes were hard as hell to press, and I had very little braking power. I started it back up, turned around and limped it home. I assumed my brake booster had took a dive since I had no power brake assist at all. My pedal was hard as a rock even with the engine running. I could also hear an air rushing sound, and the engine idle was rough.
So the brake booster operates off of vacuum from the air intake, right? So you know that loud high pitched whistle/whine I was hearing? Had to be a pin hole or small tear in the brake booster diaphragm. When I hit the brakes at the stop sign it must have finally given up the ghost and blew completely apart. And a vacuum leak will cause hesitation and rough idle. I installed a new (remanufactured) brake booster that I bought from Orielly's for about $94. No more high pitched whine, no more hesitation, and the brakes work better than they have since I bought the jeep in January. Engine also seems to run better and I am getting about 17mpg on the highway now, never got better than 14 before. I am declaring victory.
Ever since I bought this Cherokee back in January, I have been hearing an annoying loud, high pitch whistle or whine coming from the engine compartment that reminds you of the high pitch whine an old CRT television would make. It had progressively gotten louder. It was driving me crazy. I tightened the manifold bolts, no change. I cleaned the throttle body, changed the throttle body gasket, no change. I assumed my manifold gasket was bad, but I was not going to change it until I could afford a new header since it is such a P.I.T.A. to pull all that crap off to get to it. I also had intermittent hesitation issues that just wouldn't go away.
So about 4 days ago, I was stopping at a stop sign when all of a sudden I heard a loud CRACK! that sounded like a small fire cracker from under my feet. This was not a back fire or a pop. As soon as the crack was heard, my engine died, my brakes were hard as hell to press, and I had very little braking power. I started it back up, turned around and limped it home. I assumed my brake booster had took a dive since I had no power brake assist at all. My pedal was hard as a rock even with the engine running. I could also hear an air rushing sound, and the engine idle was rough.
So the brake booster operates off of vacuum from the air intake, right? So you know that loud high pitched whistle/whine I was hearing? Had to be a pin hole or small tear in the brake booster diaphragm. When I hit the brakes at the stop sign it must have finally given up the ghost and blew completely apart. And a vacuum leak will cause hesitation and rough idle. I installed a new (remanufactured) brake booster that I bought from Orielly's for about $94. No more high pitched whine, no more hesitation, and the brakes work better than they have since I bought the jeep in January. Engine also seems to run better and I am getting about 17mpg on the highway now, never got better than 14 before. I am declaring victory.
