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post #1 of 15 (permalink) Old 07-06-2012, 05:09 PM Thread Starter
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Momentary detonation?

Hi folks.
Having done the t-belt, (3 tries before it was on the marks) couple of weeks ago, and put 500 miles on it, mostly mountain 2-lane, I am now hearing a momentary ping or rattle at low-speed throttle tip-in. Like when you're creeping along in 10-20 mph. traffic and you're on-off the pedal. I can only hear it if there's a wall or barrier on both sides of the car, and windows are open. What to do/where to look? Could the belt have settled in and gone one tooth off?
The CEL has not lit. I have a basic (Autel) scan tool but haven't checked anything yet. All comments appreciated.
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post #2 of 15 (permalink) Old 07-06-2012, 08:57 PM
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Make sure that what you're hearing is not the common symptom of a slightly loose a.c. belt, that is, a metallic-sounding rattle when the engine comes off of idle when in gear as it passes thru the 1800-2200 rpm range (very brief). Correct tension is 1/4 to 3/8" deflection of belt when pressed mid-span with the thumb (tighter than you might think would be right).
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post #3 of 15 (permalink) Old 07-06-2012, 10:03 PM
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Im with the guy above,, ^^^^^

tighten the belts a few turns and see if it goes away
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post #4 of 15 (permalink) Old 07-06-2012, 10:53 PM Thread Starter
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Quote:
Originally Posted by peva View Post
Make sure that what you're hearing is not the common symptom of a slightly loose a.c. belt, that is, a metallic-sounding rattle when the engine comes off of idle when in gear as it passes thru the 1800-2200 rpm range (very brief). Correct tension is 1/4 to 3/8" deflection of belt when pressed mid-span with the thumb (tighter than you might think would be right).
You just described exactly when I hear the noise. I did change out both acc. belts when I did the T-belt, and I know the p.s. belt is not tight enough as it'll squeal at full lock. I'll adjust both of them properly and report back. Thanks guys.
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post #5 of 15 (permalink) Old 07-06-2012, 10:56 PM
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Yep...mine was at the 1400-1800 rpm range before I had the belts changed at Dan's last Fall meet.
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post #6 of 15 (permalink) Old 07-20-2012, 12:10 AM Thread Starter
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Finally got around to tightening both belts. No more "pinging", as you all said. Many thanks again, folks. One comment about the F.S.M. instructions, though. It states both belts can be adjusted from underneath. I saw no way to access the P.S./alternator belt adjuster from the bottom. Of course I had to remove the top plastic and metal to get at it, which is rather time consuming. So if you're replacing that belt, be sure you tighten it to specs first time, and avoid doing what I did.
I was also surprised at how many turns of the adjuster bolt(s) I needed to get to the 1/4" deflection recommended.
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post #7 of 15 (permalink) Old 07-20-2012, 04:48 AM
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Glad to hear your problem has been resolved. If you were off by one tooth, you would have gotten a CEL and the PCM may have also instituted a rev limiter at 2500 RPM.

Exhaust rattles can also occur at low speeds.
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post #8 of 15 (permalink) Old 07-22-2012, 02:05 PM Thread Starter
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Maybe I spoke too soon. On a 160-mile trip Friday I heard a new noise in exactly the same (1800-2200 rpm) range. It was a low moan, not unlike intake moan when secondaries open on a 4-barrel. Windows all closed, a/c fan at low, music off and freshly laid asphalt. Car in 4th lock-up, throttle opened very slightly past the cruise point for 70 mph. On older pavement, tire noise would overcome the moan, so it isn't loud. I have not checked for exhaust (or intake) leaks yet. Comments?
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post #9 of 15 (permalink) Old 07-22-2012, 03:34 PM
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Did you try it with a.c. on and with a.c. off to see if that makes a difference?
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post #10 of 15 (permalink) Old 07-22-2012, 04:01 PM Thread Starter
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Quote:
Originally Posted by peva View Post
Did you try it with a.c. on and with a.c. off to see if that makes a difference?
I believe I did, and it had no effect, but the weather was really changing at that point (t-storms passing through) so I'll re-check that. If that does make a difference, then I'm guessing the belt is now too tight?
Another question: Anyone used the Gates "Cricket" belt tension tool, and is it worth the $20 or so?
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post #11 of 15 (permalink) Old 07-22-2012, 04:55 PM
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My personal experience with the Krikit™ tools: *Total* waste of money. About 3 years ago, I bought both the serpentine and the V-belt type. I adjusted one of the serps on my 2.7 exactly by the instructions, and it was *WAY* over-tight by *any* reasonable criteria. I loosened the belt, and both tools have been sitting in my tool box unused ever since. Best tool? Your thumb - look for 1/4-3/8" deflection in belt mid-span with moderate thumb pressure - has never failed me.

Last edited by peva; 07-22-2012 at 05:02 PM.
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post #12 of 15 (permalink) Old 07-23-2012, 12:00 PM Thread Starter
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OK, did another road test yesterday. Dry pavement, long straight, older asphalt. In 4th lock-up, 2000 RPM cruise, applied light throttle. Could not duplicate the "low moan" regardless of a/c or fan settings. Had a friend with me who couldn't hear it either. I'm beginning to think it might have been a tire noise variation caused by the fresh (days-old) asphalt we were on on Friday.
Peva, I double-checked the belt tension and it is within your recommended 1/4 to 3/8 inch slack. So I don't think I'm gonna worry too much more at this point, except to ask if such a sound could be transmission-related? (Trans works fine a.f.a.i.k.)
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post #13 of 15 (permalink) Old 07-23-2012, 12:33 PM
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I don't know about the transmission as possible source of the noise. Hopefully someone else will have some thoughts on that.
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post #14 of 15 (permalink) Old 07-28-2012, 02:56 PM Thread Starter
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OK, last word on this (I hope). I checked the V-band clamp bolts for the cats, as suggested. Sure enough, I was able to take a couple of turns on the pass. side. Driver's side was frozen, so I applied some penetrant and made sure both clamps were tightened to the 100 inch-pound torque spec.(Actually went to 115 just in case) Voila, the mysterious on-and-off moans were gone! In fact it sounds quieter than it ever has, but that might be my imagination, too. Thanks again to all.
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post #15 of 15 (permalink) Old 07-28-2012, 08:55 PM
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