Hidden vacuum leak February 25, 2011, 09:25:55 PM I've got a whistling noise that started a few weeks ago and is slowly getting worse but cannot be pinpointed so I need your guys' help.First evening, I stethoscopes and found that I cannot pinpoint any single point of the noise. It is loudest somewhere below the upper intake.Second evening, I pull the upper intake, replace the relatively young hoses with new ones, install a new upper to lower, egr, tb, and iac gaskets. New hose clamps. While in there, installed larger fuel injectors and mass air sensor that I've been needing for some time. Looked over upper and lower intake for any obvious stress signs or cracks but nothing. Put everything back together, torque it all down, sound is still there. I run the engine at just above 300rpms which pulls strong vacuum and whistling is insanely high pitched and loud. We were not able to pinpoint anything like this as the frequency would just pierce through the stethoscope. Removed belt and plugged each vacuum line off but still a strong whistling noise is there.Third evening, pull intake off again, pull all fittings on lower part of upper intake, along with air charge temp sensor off lower, reinstall all with some RTV on threads. Did not remove press-in fitting in upper intake but gooped up RTV along the base and halfway up the connection to where there is a stop for the hose. The vacuum split thing on the lower part of the intake itself that goes to the car's vacuum tree I gooped up to make sure there wasn't a split between the lines. Cleaned up old upper to lower intake gasket and used a light coating of RTV to test the upper to lower seal. Reinstall everything, along with a new Accufab throttle body that the car has also needed forever. Put together and still whistling.So now what? Lower intake gasket leaking for some reason? Quote Selected
Hidden vacuum leak Reply #1 – February 25, 2011, 09:35:26 PM Does it have a high idol and have you tried spraying carb or brake cleaner and check for idol change? Quote Selected
Hidden vacuum leak Reply #2 – February 25, 2011, 09:43:12 PM 625rpm idle and it listens to anything I command it through the quarterhorse, down to a minimum of ~575 (with the IAC attached).I forgot to mention, this is a original '93 Cobra intake so it only has three plugs on the bottom and the furthest outside one is capped off.The tone at 300rpms with IAC disconnected and TB closed is up in the 3-4KHz range, it drops to like 2KHz and quieter at 625, and it tapers off when the tb is opened a little. The sound does not pulse with the motor - it is more consistent. It sounds like the air equalizes (pitch smoothly drops) with that outside of the intake when the engine is shutoff. I'm 100% certain it's vacuum but it cannot be found :( Quote Selected
Hidden vacuum leak Reply #3 – February 25, 2011, 11:26:05 PM Id spray it when you find the leak it will drop or raise the idol I cant remember which? but you'll know Quote Selected
Hidden vacuum leak Reply #4 – February 26, 2011, 12:19:17 AM Need some fluid - I keep forgetting to pick some up. I should find a smoke machine to borrow from someone ...but the hole sounds so small since it isn't a hissing, it would be difficult to see smoke getting sucked in - especially under the intake. Quote Selected
Hidden vacuum leak Reply #5 – February 26, 2011, 02:14:18 AM ahh, but you can remove the upper once more and do this....-make a dummy plate to install along the bottom of the intake and goop/seal it.-make a dummy plate to cover the TB opening and goop/seal it.-block off all but one vac tree port-now inject air into the last remaining intake tree port with a rigged up bike foot pump and listen for the leak and watch the needle like a leak down tester.see if it holds air.i wonder if your egr diaphram didnt blow a pin hole.it seems like its linear with the motion of the EGR.,,as in you pull less vac at higher R's.how are you getting those 300rpm numbers,, just by manipulating the idle ?pull suction on it and see if it holds vac manually,,,or have your gf do it,,lol Quote Selected
Hidden vacuum leak Reply #6 – February 26, 2011, 02:18:46 AM while im thinking about it, spray wd40 in the vac port of the egr, that will lub up the diaphram and change the noise or pitch to help you pin point. Quote Selected
Hidden vacuum leak Reply #7 – February 26, 2011, 06:36:10 AM If you could borrow someone's EVAP machine you can find it pretty fast. Quote Selected
Hidden vacuum leak Reply #8 – February 26, 2011, 09:00:27 AM Subscribing :) I got a whistle too, check the video in my thread does it sound like mine. Mine seems to be around the throtle body area more toward the IAC Quote Selected
Hidden vacuum leak Reply #9 – February 26, 2011, 09:46:41 AM Small crack in the vacuum tree on the firewall? Quote Selected
Hidden vacuum leak Reply #10 – February 26, 2011, 11:53:02 AM Quote from: jcassity;353997ahh, but you can remove the upper once more and do this....-make a dummy plate to install along the bottom of the intake and goop/seal it.-make a dummy plate to cover the TB opening and goop/seal it.-block off all but one vac tree port-now inject air into the last remaining intake tree port with a rigged up bike foot pump and listen for the leak and watch the needle like a leak down tester.see if it holds air.i wonder if your egr diaphram didnt blow a pin hole.it seems like its linear with the motion of the EGR.,,as in you pull less vac at higher R's.how are you getting those 300rpm numbers,, just by manipulating the idle ?pull suction on it and see if it holds vac manually,,,or have your gf do it,,lol Ah, didn't think about rigging things up. I've done this in the past for some other reason but it's a great idea if all else fails.I have NOT tested the EGR itself - didn't think of that. I'll go pull vacuum on it immediately.As for idle, it would barely run but I disconnect the IAC and back out the TB screw until the EEC showed such a lot idle. It'd be next to to dying, but it keeps running. I COULD get it slightly lower but the vacuum would drop and the whistling would begin pulsing with the firing of the cylinders. I was actually surprised that the motor was still turning at all at that point due to the seemingly long pauses between some firings.Quote from: jcassity;353998while im thinking about it, spray wd40 in the vac port of the egr, that will lub up the diaphram and change the noise or pitch to help you pin point. I will do that as well. Thanks!Quote from: kendoo130;354001If you could borrow someone's EVAP machine you can find it pretty fast. I don't know that many people in the automotive business or into working on cars :(Quote from: Bob;354006Subscribing :) I got a whistle too, check the video in my thread does it sound like mine. Mine seems to be around the throtle body area more toward the IAC Two things1) I LOVE it! 2) it's difficult to hear with most microphones but I believe yours went away when you gave it throttle, and didn't come back? Mine may be quieter at idle than yours (currently) and if it sounds close to your recording, I'd say the tone may be close to mine when pulling harder vacuum. There really is no way to compare without using a better mic and claiming that it sounds exactly the same as being there in person.Quote from: hwy73;354009Small crack in the vacuum tree on the firewall? Disconnected the tree completely and plugged off hose but the whistling was still there. At least I finally got around to replacing that hose and clamps with a new one as that single hose made my life a nightmare with the old one on the tree being crimped on. Quote Selected
Hidden vacuum leak Reply #11 – February 26, 2011, 01:59:11 PM EGR is about a year old. Holds 26 inches without an issue. Sprayed WD40 into it and no change when I started the engine. Quote Selected
Hidden vacuum leak Reply #12 – February 26, 2011, 03:41:48 PM Cleaning out the IAC was weird as spraying in one end would show the fluid coming out the other. I'm not sure how that solenoid works but I went to block off the IAC with a gasket and some steel. Whistle is still there and unchanged... Quote Selected
Hidden vacuum leak Reply #13 – February 26, 2011, 05:08:18 PM Shot in the dark: PCV valve grommet? Quote Selected
Hidden vacuum leak Reply #14 – February 26, 2011, 06:57:35 PM Okay guys - bad news. I think it is the lower intake gaskets. While the whistling did not go away, spraying the mating surface of the lower to head could cause whoosing/sucking noises on both sides of the engine on runners 2 and 6. I can only assume the whistling is another vacuum leaks where the lower meets the heads on the rear drivers side. We dumped some water on the lower intake on one side and the motor sucked most of it in, steaming out the exhaust.Likely cause but since other spots show problems and I have to replace the gaskets anyways, we'll see if that fixes everything.*sigh*Thanks for the suggestions! Quote Selected
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