Whining... Er, screaming!

The first time assembling the manifolds to the head, I noticed it was very easy to just hang the three parts (exhaust manifold, two intake runners) onto their mounting studs protruding from the head and tighten the nuts, only to find that there is enough range of motion for the intake runners to be tightened up and come to rest in such a position that the plenum would not sit down onto the four mounting studs coming from the two runners.

So now when assembling the manifolds to the head, I find it very helpful to simply place the FI plenum onto the four studs sticking out of the two pairs of intake runners, which ensures proper orientation/alignment of the intake runners, and then tighten the seven manifold retaining nuts. Once the manifold nuts are torqued, I just pull the plenum off the studs and continue with assembly until it's time for the plenum to go on permanently.

Not sure if any of that helps, but it might if you think that there's a leak where the intake runners meet the head or the plenum.

Speaking of potential spots for vacuum leaks, did you inspect the hard plastic ("bakelite") injector mounts and replace the rubber O-rings between said mounts and the FI runner castings, as well as the O-rings between the injector noses and the inner part of the injector mounts?
 
Thanks Dan -- would definitely like to use your technique for mounting the runners and torquing the manifold nuts. But I'm using an Allison's header and there is one nut that I can only (and barely) access when the plenum is off. It's impossible to properly tighten all the nuts with the plenum installed. So I typically wiggle the runners into position where they appear to be seated and flush with the manifold and then tighten it all down while I can see it.

This could be a leak but it could also be something "flapping" or resonating inside the air passages. My o-rings and injector mounts were all replaced a year or so ago but I'll double check them for cracks etc. Definitely a weird problem and I'm certain I'll need to remove the plenum to inspect everything and find the culprit.

Dan Sarandrea (Phila) said:
The first time assembling the manifolds to the head, I noticed it was very easy to just hang the three parts (exhaust manifold, two intake runners) onto their mounting studs protruding from the head and tighten the nuts, only to find that there is enough range of motion for the intake runners to be tightened up and come to rest in such a position that the plenum would not sit down onto the four mounting studs coming from the two runners.

So now when assembling the manifolds to the head, I find it very helpful to simply place the FI plenum onto the four studs sticking out of the two pairs of intake runners, which ensures proper orientation/alignment of the intake runners, and then tighten the seven manifold retaining nuts. Once the manifold nuts are torqued, I just pull the plenum off the studs and continue with assembly until it's time for the plenum to go on permanently.

Not sure if any of that helps, but it might if you think that there's a leak where the intake runners meet the head or the plenum.

Speaking of potential spots for vacuum leaks, did you inspect the hard plastic ("bakelite") injector mounts and replace the rubber O-rings between said mounts and the FI runner castings, as well as the O-rings between the injector noses and the inner part of the injector mounts?
Click to expand...
 
Update: I removed the plenum and found that a few of my vacuum line connections were plugged and cleaned them out. Not sure that had anything to do with this problem but it certainly wasn't helping. Inspected everything on the plenum, butterfly valve, intake runners, gasket, etc and didn't see anything unusual.

Put everything back together, and... Still making noise. But making a less noise. More like a whistle than a scream now. AND I'm able to drive the X again now that my coolant leak from the heater elbow is (mostly) gone. The whistle completely goes away under load. So when I'm idling or coasting I can hear it. But if I accelerate under load (i.e. not in neutral) it goes away. ...and the stethoscope still suggests the origin of the noise is the intake plenum and/or runners. Still a mystery...
 
geekdaddy said:
......The whistle completely goes away under load. So when I'm idling or coasting I can hear it. But if I accelerate under load (i.e. not in neutral) it goes away. ...and the stethoscope still suggests the origin of the noise is the intake plenum and/or runners. Still a mystery...
Click to expand...

Load=low vacuum, no load=higher vacuum.

Hmm, could be an indicator of a vacuum leak. Consider that clogged vacuum hose ports would have allowed a higher vacuum than intended by design, and unclogging them lessen the vacuum to nearer to stock levels.

If you are having trouble getting the idle down to stock specs, could also be another indicator of a vacuum leak, as in too much air. (But note that the performance head and cam will also alter stock idle characteristics.)

Try Papa Tony's unlit propane torch technique to probe for vacuum leaks. An overlooked area on FI cars is the quality of the seal around the throttle shaft. Shaft bushings can wear, and seals can get old and soft-fail.

And how did you get your elbow leak under control? Edit: Nevermind, just saw your update in the thread you started on the leak (HA! Moore's law applies to Teflon tape, too "If some is good, more is better!":) )
 
Vacuum leak noise...

Vacuum leak noise can sound like a scream. On a neighbor's truck, I fixed an intake manifold gasket leak that screamed. We tried sealants applied to the exterior at first, but they eventually would not work. So changing the gasket fixed it.

Originally your noise started in the middle rev range, and wasn't present at idle, now it sounds like the opposite.

I'd look at the idle screw which is a sort of bypass air adjustment on the throttle body. Check for an o-ring there, perhaps it got sucked in.
 
I'm really beginning to question my gaskets from the runners to the head and the runners to the plenum.

The head has changed, but the vacuum lines, plenum, runners, etc. haven't. She's running fairly well now. Idle is a bit rough when cold but smooths out at temp and power/response feel good. I'm not pushing the engine very hard right now since I'm still breaking in the cam and head.

So I'll need to tinker a bit and will hopefully have some ideas by the time I have to pull the plenum and some other items to get at the head bolts.

budgetzagato said:
Vacuum leak noise can sound like a scream. On a neighbor's truck, I fixed an intake manifold gasket leak that screamed. We tried sealants applied to the exterior at first, but they eventually would not work. So changing the gasket fixed it.

Originally your noise started in the middle rev range, and wasn't present at idle, now it sounds like the opposite.

I'd look at the idle screw which is a sort of bypass air adjustment on the throttle body. Check for an o-ring there, perhaps it got sucked in.
Click to expand...
 
whitsle or screech?

if a whistle drone had to be a major vacuum leak.
put a carb on a corvette once and left the carb washers on the studs beneath the gasket and she screamed like a banshee.
but if you had a water leak at the front of the engine it might be water residue on the v-belt. I hate to say it or promote as the right thing, but a little spray on the v belt with wd-40 (not too rubber friendly) to see if the noise goes away.
mikemo
 
ONE MORE TIME GREG...

I see NO mention of you PROVING a vacuum leak and then isolating it...

"Why not (make a mess) and use WD40 and squirt it all around the suspected area(s) while the engine is running and screaming. Hopefully you can do this at an idle or at a steady speed so you can hear and see the engine accelerate when the extra fuel (WD40) is sucked in... An UNLIT propane torch will work as well..."

This really WORKS and HTH...
 
I had a major vacuum leak

when I first purchased my car. Turns out the bakelite seats for the injectors had cracked, sucking in air around the injector itself. I used carb cleaner to find my leak if memory serves. Short bursts at suspected areas are all that's necessary.
 
If you want to check the belt a quick spray of plain water onto the moving belt will make a noisy belt worse - and a quick shot of "armour all" (which is just silicon - so a silicon spray would also work) onto the rotating belt will quieten it for a few seconds. Its not a cure - but a diagnostic technique.
 
+1 Tony

You need to ensure there are no vacuum leaks.

The easy, non-OSHA approved method of doing this (in a well ventilated area) is getting a spray can of brake parts cleaner with a straw, and spraying all of the areas where vacuum leak is suspected, while the engine is idling.

- Manifold to head
- Runners to Manifold
- Throttle body
- All four injector seats
- Manifold snorkel connections to manifold and AFM
- Crankcase breather
- Auxiliary air valve and hose connections. The one to snorkel, one to manifold. This is the most common location for leaks.
- All vacuum connections to distributor, and AC components

If the cleaner finds any of these vacuum leaks, you will immediately hear the motor change tune as soon as you hit the problem spot.

-Matt
 
It's (at least) the runners

Another good call by Tony (and others) :clap:

I preferred Matt's suggestion to use brake cleaner. Easy and keeps things clean. Sprayed injectors/mounts and intake manifold with no change. But spraying the runner-to-plenum joint resulted in a response from the running engine. I have the bolts very tight but am using a new gasket which apparently isn't working well for me. The old one seemed to work ok but I discarded it.

Matt Brannon - Midwest Bayless said:
You need to ensure there are no vacuum leaks.

The easy, non-OSHA approved method of doing this (in a well ventilated area) is getting a spray can of brake parts cleaner with a straw, and spraying all of the areas where vacuum leak is suspected, while the engine is idling.

- Manifold to head
- Runners to Manifold
- Throttle body
- All four injector seats
- Manifold snorkel connections to manifold and AFM
- Crankcase breather
- Auxiliary air valve and hose connections. The one to snorkel, one to manifold. This is the most common location for leaks.
- All vacuum connections to distributor, and AC components

If the cleaner finds any of these vacuum leaks, you will immediately hear the motor change tune as soon as you hit the problem spot.

-Matt
Click to expand...
 
Dan made a good point in the first post (of this page). I have also struggled a bit to get alignment of things such that all will tighten up evenly and seal well, could be you just need to loosen and rearrange and retighten does it, unless the gasket is now trashed of course.
 
All Good Greg... glad you found it. Now...

Split the plenum and remove the gasket... visually INSPECT the gasket to see if you can feel or see where it is failing to seal. Look at the FLATS on the plenum halves as well.

If there is NO damage... I would simply use a good gasket sealer like Permatex GREY and coat BOTH sides of the gasket and reassemble. (Others are gonna chime in now with BLACK and CLEAR and WHITE and RED and on and on... even a coating of VASELINE will do also!)

Then RE-TEST with the Brake Cleaner.

You should be good to go!
 
Last edited:
SUCCESS!!!

Well -- I've solved the problem. Thanks in (massively) large part to the advice here.
- It WAS a vacuum leak.
- I found it by spraying brake cleaner around susceptible areas (and using a stethoscope)
- It was isolated to the passenger side runner area.

...and I found one of the runner-to-plenum studs was loose. I removed the stud and temporarily threaded a stainless hex bolt that passes thru the runner threads, and was able to tighten it down snug. Took the X for a spin tonight and.... No whining. AND no leaks from my heater elbow. I'm a very happy X owner (and finally driver).

Feeling pretty stupid that I did not find something so simple. Rookie mistake. I ruled-out the plenum because I had changed nothing but the gaskets. But me thinks I partially backed out the stud when I removed the nut at the beginning of my project and never noticed it. That was the root-cause. Oh well... Thanks again for all the suggestions here.

Black-Tooth said:
Split the plenum and remove the gasket... visually INSPECT the gasket to see if you can feel or see where it is failing to seal. Look at teh FLATS on the plenum halves as well.

If there is NO damage... I would simply use a good gasket sealer like Permatex GREY and coat BOTH sides of the gasket and reassemble. (Others are gonna chime in now with BLACK and CLEAR and WHITE and RED and on and on... even a coating of VASELINE will do also!)

Then RE-TEST with the Brake Cleaner.

You should be good to go!
Click to expand...
 
Hey Greg... we have all been there... unable to see...

the proverbial forest for all the trees... and it takes a reasonable man to say he made a mistake. I hate to tell you the number of mistakes I've made (2) in the last 16 years and wanted to kick MY mechanic in the arse for being such a dumbo!

HA!

I now try to invite friends over to help so I can then BLAME THEM for ANYTHING that might go wrong... Works for me!
 
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