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post #1 of (permalink) Old 05-03-2007, 11:05 AM Thread Starter
 
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Squeeling throttle body

Since last weekend the GM TBI on my jeep has started to squeel pretty much consistantly at about 1/8-1/4 throttle. At first I thought it was something to do with a ported vacuum hose, but I can't find any split hoses or missing hoses or capped off connections. Its a loud annoying whistle at cruising speed. The engine runs perfectly otherwise, and idle speed does not appear to have been increased. Its not there at idle, and its not there at 1/2 throttle or more. Seems to change pitch a bit when I wiggle the throttle arm, but I'm not certain. Any ideas? You can hear me coming a block away. I took off the air cleaner and leaned over the engine with a tube up to my ear, but high pitch whistles don't seem to travel down tubes too well. It sounded like it was coming from one of the throttle bores, but I certainly could be wrong. Nothing looked out of place down the bore.

Last edited by TiminMb; 05-03-2007 at 12:50 PM.
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post #2 of (permalink) Old 05-03-2007, 02:16 PM Thread Starter
 
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Anything else that could whistle like that on the manifold? Only does it when the throttle is tipped far enough, but doesn't at half throttle or more. Extremely annoying. Its like having an open ported vacuum port.
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post #3 of (permalink) Old 05-03-2007, 02:50 PM
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I think whistles like that are usually caused by the IAC bypass. Try cleaning that.

Brian.

84 CJ7 HO head, MegaSquirt, T18/D300
88 S10 Ext Cab 4.3 Auto (sold)
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post #4 of (permalink) Old 05-03-2007, 02:51 PM
 
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I'm awaiting an answer to your question, also. I've googled "TBI whistle" ten ways from Sunday and not come up with much. My Howell was howling not too long ago. I read somewhere that the Idle Air Controller can sometimes get a piece of something stuck in it so that it doesn't seat all the way . . .
The squeal would change pitch with throttle position, disappearing at highway
pedal, returning when I let off. And then it would just go away by itself.
Mine wouldn't start singing until it got warm, and then it got as loud as you say yours is. People turning their heads in adjacent vehicles at the signal stops, on the sidewalks . . . I removed the IAC and cleaned it with WD40 and blew out its mounting hole with compressed air - the squeal changed pitch but was still there - for a couple days, while I googled my arse off looking for anything on the subject - and then it stopped doing it entirely. Hate that. I want to know whats happening! Its squealed at me as I stood there with the hood popped, air cleaner off, looking directly at it, and I couldn't even triangulate the position of the source of the squeal - I moved my hand around, wiggled hoses, covered apertures, nothing changed the sound -
and then it would stop. Frustrating.
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post #5 of (permalink) Old 05-03-2007, 04:00 PM Thread Starter
 
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That something I'll look into. I'll pull the IAC device out (gutted one in my case) and block it off entirely with a plug. See if that cures the problem and then I'll know the source. I'm not running an Iac, just a gutted one plumbed into a thermal air control device that varies air flow depending on ambient temperature and an internal thermal device. Its similar to an electric choke. You can get them off european cars at the wrecking yard.
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post #6 of (permalink) Old 05-03-2007, 05:42 PM
 
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Wow - I guess since you have a Megasquirt, you can tell the computer to ignore the absence of an IAC? My GM ALDL system would throw major conniption fits.
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post #7 of (permalink) Old 05-04-2007, 10:30 AM
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I have MegaSquirt also. Yes, you can disable IAC or you can also use a PWM valve like fords used.

You can probably do the same thing with the GM based system, just need to burn a custom chip.

84 CJ7 HO head, MegaSquirt, T18/D300
88 S10 Ext Cab 4.3 Auto (sold)
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post #8 of (permalink) Old 05-04-2007, 11:14 AM
 
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I haven't formed any desires beyond the GM system, so I will tend not to try and "improve" it until then. I'm still purging the years of Carter BBD tyranny out of my soul. When I was first looking at EFI, I considered the Megasquirt, but utlitmately opted for the predesigned and CA legal Howell kit.
I'm still enjoying the performance - and I even caused another guy in my jeep group to go Howell, when he noticed how easily mine started on cold, high elevation mornings on the Dusy trail.
Its just this whistling issue - what is (are) its cause(s)?
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post #9 of (permalink) Old 05-04-2007, 11:31 AM Thread Starter
 
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If you do a search on the net under whistling GM TBI, there are posts galore and no answers. Maybe my throttle shaft is worn out? I did get a stuck throttle once this winter. Perhaps its worn and the butterflies are not seating like they intended. The only thing I have against this and vacuum leak theories is that my idle speed is not higher.
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post #10 of (permalink) Old 05-04-2007, 11:31 AM
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Quote:
Originally Posted by TiminMb View Post
Since last weekend the GM TBI on my jeep has started to squeel pretty much consistently at about 1/8-1/4 throttle. ...
Did you change anything (like the air cleaner) just prior to the whistle starting?
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