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Old 06-18-2012, 09:55 PM   #1
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1995 YJ whistle and CEL

Hello all,
I recently took my new-to-me 1995 YJ with 4 cyl, 5 spd, and 115k to the mountains. As I climbed a long grade with the throttle buried, I noticed a new whistling noise. It sounded just like a turbo - it increased in pitch with throttle position, becoming more of a loud hiss at WOT, and changes in pitch lagged throttle input. The sound did not correlate with engine or vehicle speed. At the same time I felt power loss, which I thought at first was altitude, except except that while climbing another grade, with the throttle floored, the hiss suddenly stopped and I instantly felt a significant power gain. This happened twice in the mountains, and has not happened again in two weeks of driving around at sea level.

I checked codes today and got a 12 and 51. I believe 12 is less than 50 power cycles and 51 is Oxygen sensor - lean condition.

What could cause this intermittent whistle and power loss? Has anyone experienced something similar?

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Old 06-19-2012, 12:54 PM   #2
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You probably have a vacuum leak!!

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Old 06-20-2012, 12:41 AM   #3
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Would a vacuum leak cause power loss? Has anyone had a vacuum leak that suddenly went away, resulting in power gain?
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Old 06-20-2012, 12:51 AM   #4
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It can result in a poor idle, so I would think so. Not a pro by far but if you go looking for it grab a can of carb cleaner and spray around. When you hit the cracked line the motor will rev up (btw.. Have your Jeep on and out of gear when testing)..
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Old 06-21-2012, 12:04 AM   #5
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The hiss came back today and the CEL is back on, with the same 2 codes. Power seemed down, though it's hard to tell when there isn't much to begin with.

Here's my theory:

The catalytic converter has been rattling for a couple months and is getting worse. I think it's obstructing the exhaust, causing power loss, and the hissing noise is exhaust rushing through the collapsing catalyst matrix. (Noise due to a vacuum leak should decrease with open throttle; manifold vacuum is greatest with a closed throttle.) The exhaust backup causes the O2 sensor to read improperly, throwing a code. Further evidence is the fact that the issue is precipitated by WOT operation - in the mountains and this afternoon when I got tired of the right-hand lane.

Any takers?
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Old 06-21-2012, 07:12 AM   #6
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i'm with you on the CC......mine had the same problem and new cat cleared it right on up..
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Old 07-06-2012, 08:08 PM   #7
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I finally got around to getting the cat replaced. The matrix was almost completely gone, except for a chunk lodged sideways at the rear of the cat. Also the mounting rod at the front of the cat had broken off, leaving a hole, which was probably causing the whistle before it got too big. The rig is a lot quieter, maybe a bit more power, and I haven't had a CEL. On the downside, the missing matrix material from the old cat is now rattling around in my muffler. So if your cat is going don't wait too long unless you want to listen to it for a long time.
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Old 07-06-2012, 11:19 PM   #8
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My Jeep didn't come with one. Just a really busted up muffler. Got to replace the whole deal.

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