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Resonant "wooo" ing from intake 1984 Datsun Maxima 810/910


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Okay, I'm almost ready to leave for California on my vacation.  Should be a blast.  I have enough tools to rebuild a few Datsuns, just in case.  This will be Wynona's maiden long voyage.  She's been running quite well, except for one little issue.

 

At around 2000 rpm and sometimes 2500 rpm, at light load, there is a resonant woo noise coming from the flapper box AFM.  I'm not convinced it's just the flapper box, but at least that's where it's most noticeable.  Hold it at that load at that rpm and it continues wooing, like blowing across a bottle top.  Put your foot into her, or let off, it goes away.  It seems a certain vacuum load is reached and it just does it.

 

My Maxima race car with a 5 speed does NOT do it.  Or at least I've never noticed it.  It is quite a bit louder, it's possible I can't hear it and seeing as I'm usually driving it harder, I may not be in the rpm range to have it occur.

 

On the wagon, I have changed the following:

 

I have replaced the exhaust with 2 1/4" all the way to the back, replacing the cat with an aftermarket cat and aftermarket muffler.

I have opened up the airbox by cutting the center top out and installed a drop-in KN filter.

I have bypassed the thermal vacuum valve and the BCCD assembly, and the EGR, all in hopes of killing the noise, as the race car has none of those in operation.  The race car also doesn't have a cat, but I doubt that would make a difference.

I have replaced the stock ignition module with a '79 280zx module to get rid of the idle control/hot start non-performance module.

 

As far as fixing the problem,

 

I have replaced all the major vacuum lines and I've run vacuum checks until my eyeballs pop out.  It holds steady vacuum, no leaks.

During the cold weather, the wagon didn't make this noise, or at least it wasn't apparent.  With the warmer weather, it's much more noticeable and louder and repeatable.

 

The automatic transmission has only one hard line feeding it with two very short sections of vacuum tubing to connect it.  They are both good.

 

When the "woo-ing" occurs, there is no runability issue.  RPM holds steady, transmission doesn't shift weird.  It just makes a vibratory resonance.  I've tried wrapping rubber around the AFM, it doesn't seem to help.  I'm rtving a small chunk of innertube to it right now, just for giggles.  Doubt it's going to do anything.  I may need a thicker chunk of rubber.

 

Anyway, I'm going on the trip regardless.  While I'm on that trip, if the wonderful Ratsun community has any ideas how to solve this problem, or even experience with the same problem, I'd love to hear it.

 

Again, '84 Maxima wagon, L24E with automatic.  House- "These are your clues, go!"   ;)

 

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Matt I doubt this has anything to do with this but after '82 the ignition module (matchbox) was changed from E12-80 to E12-93. The E12-93 has two extra terminals on the side. These connect to the ECU and allow it to introduce up to 10 degrees of retard to the ignition for 'fine tuning'.
 
This is from an '84 Maxima and has an extra I and W terminals....
L24Eignition003Large.jpg
 
 
This is the insides of a regular E12-80 matchbox...
 E12-80EImodule.jpg


This is the insides of the E12-93...
E12-93EImodule002Large.jpg

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Wynona is still doing well and still making the noise. Will find it when I get home. And for the record, 550 go road race mustangs are REALLY fun! Heading up from red bluff now.

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FOUND THE SQUEAK! And appropriately, at Canby! Stopped in to Napa by the fairgrounds and I will now continue on squeak-free towards home. I'll give you all some guessing time before I post the answer today or tomorrow. Very happy. :D

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IMG_7452_zpstq7svva6.jpg

 

See the little tiny can about two vacuum lines from the EGR valve?  (Yes I know the EGR is disconnected.)

 

IMG_7453_zpsvsqqnnzr.jpg

 

Follow that along the firewall with the AC tubes, and it exits out at the cruise control.  Specifically a tee connector that goes to the various functions.

 

IMG_7454_zpsgtsrwymc.jpg

 

You can see it a little better here.  The leak was on the passenger side, but it sounds like it's coming through the intake.  Very odd.  We tried pinching off that little can line during testing, but dumb me, it connects the tee which goes back to a bunch of smaller lines, all of which are connected to cruise control function and they come in a little behind that can on the manifold.  So pinching off the tiny can one doesn't do anything, it just sucks from the other side of the tee.

 

Funny enough, even with that vacuum leak, the cruise control worked fine.  It must have been just tiny enough to not cause a problem then as the trip progressed, it opened up more.  The cruise system was one of the only ones I didn't replace before the trip, mainly due to lack of time.  Took me a half hour or so to carefully replace them at the Canby NAPA.  Started out with replacing the PCV valve in the hopes it might be the squeak.  After that, I started yanking lines I hadn't before and that's when I found the issue.  Working that break on the passenger side of the car led to all sorts of squeak noises which could be modulated.  Lol.  Sounded like a set of horns in my intake!

 

When I vacuum tested the manifold, it didn't have a vacuum leak.  I'm guessing it was just tiny enough then to meter or just not show on the vacuum gauge.  The cold Oregon weather opened it up a bit more.  So there you go.  Regardless of the squeak noise sounding like it's in the intake, look elsewhere to things you HAVEN'T fixed.  ;)

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