[asavage]

Clay came up to Carlton today, and we spent some time with his '82 720. The exhaust is tight and very quiet by my standards. However, there is considerable intake noise. His 720 has only the second air intake plenum without cracks I've seen. Stock air filter.

We came up with an idea to line the wall of the OEM air filter canister with 1/4" foam. I think that may be effective. The canister intake is facing the driver's side inner fenderwell: a sheet metal wall.. Possibly opening up the fenderwell, or alternatively making that wall of sheet metal acoustically porous (gluing foam to it) are other ideas we kicked around.

One thing I forgot (because his SD runs so smoothly) is that the valve clearances should be checked. A tight intake valve might exacerbate the intake noise, but that's kind of a stretch. But, since adjusting the valve clearance is a routine maintenance item, it might as well be eliminated as a possibility.

Les Schwab took over $300 for a front brake job on the truck, and it pulls to the left severely on application of the brakes. Tested on gravel, the LF seems to be the culprit. We pulled both front wheels and swapped them side-to-side (because it also drifts left a bit even when not braking) and although the rotors are new, the calipers are rebuilt units, and new hoses, it still pulls. No dragging of either side.

Schwab told Clay that it might be the rears, but that they couldn't get the drums off! Twenty minutes later, we had them both off, nothing untoward back there, all springs present, about 50% wear on all pads, no wheel cyl. leakage. So much for that.

The next logical step (for me) would be to suspect a faulty rebuilt caliper, even though all four pistons are free (I checked), but we lacked time today to swap them side-to-side. Clay is going to revisit the issue with Schwab, now that the drums are "loose".

Clay, the 720 idler arm info is in this thread. I remembered wrong, the new idler arms are more money than I remembered. However, I see mention of two different types of bushings for replacement. Possibly the bushing OD of the ones you obtained are too small?

Next, the left turn sigs work but when MF switch is moved to the right, only the dash right arrow indicator lights, not the lamps. Schematic and wiring diagrams for it are here. After reviewing it, and because the dash indicator is directly wired to the same harness as the turn sig lamps front and back, I have to say: check the lamps themselves first, then their grounds, then start looking upstream for a cut wire between connector 77M and the instrument cluster area. The wire will be Blue/Black.

[philip]

Clay came up to Carlton today, and we spent some time with his '82 720. The exhaust is tight and very quiet by my standards. However, there is considerable intake noise. His 720 has only the second air intake plenum without cracks I've seen. Stock air filter.
SNIP
One thing I forgot (because his SD runs so smoothly) is that the valve clearances should be checked. A tight intake valve might exacerbate the intake noise, but that's kind of a stretch. But, since adjusting the valve clearance is a routine maintenance item, it might as well be eliminated as a possibility.

How about ... ?

1). exhaust is too restricted due to carbon choke, pinch, etc.
2). injection timing set way off ideal set (18-20 degree for stock).
3). (another exhaust) the exhaust pipe is not locked next to the transmission support.

When I bought my truck, the oem muffler was choked. Not anymore. Replaced with a "straight through" resonate used from a late Camry. LOL

Also, as Al laughed ... I replaced the oem air filter and cannister with a air breather system. No different in quiet intake noise ... except when nearly 4000 rpm (which I rarely do).

[asavage]

Also, as Al laughed ... I replaced the oem air filter and cannister with a air breather system. No different in quiet intake noise ... except when nearly 4000 rpm (which I rarely do).

My personal opinion is that Philip is getting kind of deaf

Seriously, Clay's truck has quite a bit of intake noise, but the exhaust is very quiet.

[philip]

My personal opinion is that Philip is getting kind of deaf

Seriously, Clay's truck has quite a bit of intake noise, but the exhaust is very quiet.

What? WHAT?

You guys need more exhaust ... to balance your intake.

Ok ... is one or more intake valves that is passing combustion? Valves that are burned, valve lashes too tight, lots of carbon in the intake passages? My truck had a restricted muffler when I first got it. I'm ok now with that used Toyota Camry resonator only.

[asavage]

... is one or more intake valves that is passing combustion? Valves that are burned, valve lashes too tight, lots of carbon in the intake passages?

Yes, I mentioned all but the last. It runs very well (if a bit down on overall power, but then I haven't driven an SD22 in quite a while and have become used to 80HP in the LD28). I did wind it up a couple of times, and it pulls clean (no smoke) and smooth, if a bit breathy.

I think checking the valve clearances a good investment: even if they're OK or close, it's a scheduled maintenance kind of thing anyway, and establishes a baseline. I don't know that I'd recommend a compression test just for this symptom. And carbon in the intake? This is a non-EGR engine, where would the carbon come from?

[philip]

-SNIP- I think checking the valve clearances a good investment: even if they're OK or close, it's a scheduled maintenance kind of thing anyway, and establishes a baseline. I don't know that I'd recommend a compression test just for this symptom. And carbon in the intake? This is a non-EGR engine, where would the carbon come from?

Would you say this audible thrushing, howling, "resonate" noise air(:shock:) is heard from the intake throttle body? Or is the resonate honking noise exiting at the air filter canister? So what? But if there is crackling/bark also coming from the intake manifold then there should be cylinder combustion pushing back into manifold. Since that engine does not EGR, it should not have a bunch of carbon around the throttle body. If you do find quite a bit of carbon then ...

I still question the exhaust pressure system. But what do I know from what I have only read about here.

Got a .mp3 for us all to hear?

[claybodie]

Yes, should you ever be so lucky as to have a chance to meet Al Savage, take it! He's incredibly knowledgeable/helpful and we did about 3 months work of diagnostics in about 3 hours.

Awesome. So today I'm going to experiment with the air intake and see what happens. Any ideas on what sort of material I should use if I extend the intake hole? I was just going to grab some plumbing pipe from the hardware store and try to find somewhere else to bring air in. Al mentioned cutting a hole in the wheel well?

I'll be reporting as the story develops further

Clayton

[claybodie]

Does it talk about the air filter housing anywhere in the shop manual? I can't find it. Is it standard for the housing to just have a hole in the side like mine does?

[claybodie]

Ha! So here's a diagnostic tool I should have discovered a long time ago: 1/4" flexible plastic tubing. The last time I was at the exhaust shop, a mechanic there had a stethoscope consisting of the ear pieces and a tube. He used that to determine whether or not the truck had an exhaust leak (it doesn't) You can do the same thing with any plastic tube: put one end in your ear and use the other end to find noise 'hot spots'.

At an idle, the noisiest places are on the intake side of the air filter housing, and also under the exhaust manifold shielding where all the noise is bouncing around.

I also discovered that there is more noise coming in from the left-most vent in the cab than anywhere else! Damnit, that vent doesn't even work!

So I'm going to plug that vent first with sound insulation, then wait for a friend so I can have him rev the engine for me (I haven't fixed my throttle knob yet).

[claybodie]

I took the air filter housing out and thought about it for a few minutes...
Al - do you think that insulating the actual housing is going to help, or is the noise just coming from the intake?

I'm thinking about insulation the outside of it with sound insulation, but I don't want to waste material. I'm not sure where I'm going to route the intake either...

[asavage]

I use a length of garden hose or heater hose for pinpointing sound. Pity I didn't think of that Monday, but then again . . . I got it right without

I would use porous-face insulation glued to the interiour of the AF housing, as we discussed. That means: you can't just use that foil-backed stuff, it won't absorb sound, only damp it a little and reflect it more.

Because it's cheap and easily modified with standard tools, I would use white or black PVC pipe for your duct experiments. I keep coming back to my Dremel for this kind of thing.

My thinking was to move the intake sound to the area in front of the LF wheel. Downside (as mentioned) is that your air filter will get dirtier, faster. Upside is that it will be relatively easy to cut a suitable hole in the inner fenderwell and mount a short length of PVC to it, using ell brackets or whatever, and a flange or soft insulation collar arrangement where the new PVC duct meets the AF housing.

Or mount the duct rigidly to the AF housing, make the fenderwell hole oversize, then have the duct slide through the fenderwell as you remount the AF housing in place. All kinds of ways to skin this cat.

Vent: on the non-A/C models, it connects directly to the cowl. If you open the hood, open the left vent, and bend down and look through it, you can see right into the engine compartment! There is supposed to be a foam seal around the hood's hinge plate that seals engine fumes and noise from the cowl when the hood is down. If it's gone, use your foil foam to make a new foam gasket there, it might make a large difference. Damping the noise before it reaches the cowl will be more effective than stuffing a sock in the vent, when the cowl is already propogating the noise.

[claybodie]

By god you are a wealth of knowledge!

I'm going to plug up the hood-hinge right now and then work on the filter. How much space do you think the filter needs in there? If I leave about 10 mm of space, that gives me 5.5 mm of padding space.

One question about routing the pipe from the AF - if it goes into the wheel well, won't water intake be an issue (considering we live in the PacNW)?

[asavage]

You might be able to put a 90° downspout on the duct after it comes through the fenderwell. Since you won't be removing the AF housing every week, a single sheet metal screw or equivalent would fasten the 90° elbow to the portion of the duct coming through the fenderwell. If you ever had to remove it, you could.

If you glued it together (as if it were plumbing) you might have a tough time later if you needed to remove the AF housing for some reason.

As for clearance, 5.5mm = ~.220" = ~<1/4". If you recall, I was thinking about 1/4" foam (the stuff that comes to mind is the thin black or grey foam that comes with motherboards, or used to anyway: not the pink stuff.

I tend to use 3M 777 spray adhesive, but I don't know if it will melt that foam.

[claybodie]

Alright, here we go. I can't believe how well you diagnosed the problem Al, but all that noise - the deep reverberation the goes right through my skull - is coming from the air intake.

Not that I didn't believe you before, but today I was finally able to hear pinpoint the source. Here's what I did:

First, pulled out the filter housing and tried padding the inside. Great fun, but I don't think it did much:





The next weekend I went to the hardware store and bought a 2 5/8" hole saw for my drill and cut a nice little hole in the side of the engine compartment. Boy was that fun!

you can see the circle to be cut in black marker:








While at the hardware store, I also bought some 2" PVC pipe that fits perfectly into the inlet of the air filter housing.





So I put the filter housing back in with the PVC tube sticking into a nice little compartment in the wheel well, in here:



This is what it looks like with that mudflap thing pulled back, looking up from the wheel:






Ok, so what happened?
Well, I think it got a lot quieter. The reason I'm not sure is that it's still loud, but now it's wind noise instead of chest-thumping reverberation. If it isn't just in my head, it seems like that small 25 minute step made a huge difference.

I finally proved it to myself today by doing the following:
I locked the throttle at high rpm (by the way Al, this took me 2 seconds to fix without installing the one you sent me, I just had to see what it was supposed to look like - just put those plastic tabs back in place) and knelt down next to that pvc tube and partially covered it. When I did that, a good 25% or more of the overall engine's noise went away - and no, I didn't kill it, there was still plenty of air flow, but it was limited the amount of engine explosion noise that could come out of that pipe!

Awesome!

So now I'm all about figuring out the best way to capture that noise. I just put a bunch of sound dampener in that area, and I'm scheming about some kind of sheet metal box I could trap the noise in.

Any ideas? I've heard other vehicles have noise killers on their air intakes - can I get one of those?

-Clayton

[asavage]

I have searched for quite a while, not finding the pic I'm looking for.

You can just make out the intake muffler in this shot:


OK, eBay to the rescue: 1980 Olds Toronado (29k orig miles):


IIRC, my '83 G30 (6.2l) had a similar setup. It's a big plastic oval, with lots of deadening material, and a straight flow path through. It has NO restriction to airflow, but most "tuners" take it off, thinking they're reducing resistance (ugh).


1983 Chev Blazer (military) w/6.2l. Does not look quite like the civilian intake muffler:


1982 Chev 3500 (1T truck) w/6.2l



1980 Cadillac Eldo Biarritz (37k orig. miles), 5.7l diesel: