Soundproofing

[recurve]

Here's something interesting. Our '95 Blazer LS is *much* quieter than our '97 Blazer LT. It's not related to highway driving or wind noise either. It can be heard at low speeds and even at idle.

At first I thought that maybe the the '95 had better soundproofing in the hood; however, with each hood propped open and running at idle, the '95 engine is much quieter than the '97. Quite odd, because an LT should be more luxurious and if anything quieter than an LS model - but the opposite is true.

Any ideas?

Thanks,
-- recurve

[metallica21156]

i have a 95 blazer and theres a valve on top of the motor for the way the intake works. when the motor is at idle and a little above its tapping. after higher rpm it stops. the 96 blazers and up don't have this. it was only on there from 93-95. help you?

[recurve]

Hi Metalica. Thanks for the input but… if it makes a tapping noise in the '95, that would make the '95 louder than the '97 Blazer. Actually I don't hear the tapping in the '95 and it is much quieter than the '97.

The '97 makes a louder roar that is easily heard. My friend is an autobody mechanic and more familiar with Hondas and Toyotas. When I showed him both of our trucks he assumed the '97 had a bigger motor, like a V8. When I told him they are basically identical 4.3 L V6 engines he didn't believe me and had to double check the specs. Then he just shrugged his shoulders and didn't know why it was louder.

Actually, this '97 has had two engines in the few months we've acquired it. The "new" engine came from a junkyard. Both engines made this kind of roar so it is not specific to the engine.

I'm wondering if the air filter might be to blame? I'm about to order one of those oiled sponge air filters from AMSOIL and see what happens.

Thanks,
-- recurve

[metallica21156]

i have a custom intake on my truck and its a little louder but not much. just better performace.

[Trail Blazin96]

does it sound loud when you hit the gas? Or is it just when it is idling, mine sounds louder than it used to and some are telling me it is the Fan clutch, when i hit the gas the engine has this roar, and it will let off when i am not touching the gas.

[recurve]

It does have a significantly louder roar when I hit the gas… Sounded really cool and powerful the first time I heard it but got boring real fast. However even at idle, the '97 Blazer is much louder than the '95 with both hoods open and listening to them from outside.

So you think it might be the fan clutch? I'm not sure where the fan clutch is or what it does. You have a friend who replaced the fan clutch and the roaring stopped?

Metallica, I think what I got is stock on the truck (not a modified intake) but I really don't know. Both our '95 and '97 Blazers we acquired used.

Thanks,
-- recurve

[Trail Blazin96]

No my truck makes the noise and I haven't had a chance to fix it yet, it just started making the noise about 2 days ago

[Trail Blazin96]

I have a Thread going right now about the Engine fan keep an Eye on it and hopefully we can find out what the heck is goin on with our trucks!

[recurve]

Thanks Trail Blazin. here is the link to your engine fan thread (in case others are interested):
http://www.automotiveforums.com/vbul...d.php?t=298939

[Trail Blazin96]

your welcome recurve

[BlazerLT]

Also, a growly exhaust can be telling you that your cat is partially plugged up.

[metallica21156]

how does a growly exhaust sound? mine sounds like a high toned flow master and when is really being floored it sounds like its growling but picks up speed real fast.

[twodoorblazer]

Um, couldn't it be the 95 has a CPI 4.3L and the 97 has the cfsi 4.3L

[recurve]

Hey twodoorblazer, you may be onto something.

I checked the fan blades over the weekend and it seems to flow freely. Right now I got the ignition switch halfway out and I can't turn on the engine. I just moved the fan blades with my fingers, it doesn't seem to be that the clutch is broken (and hence causing the roar). So I guess something else is the culprit - perhaps it could be the different type of fuel injection (as you said).

CPI -> Central Port Injection
SFI -> Sequential Fuel Injection

I'm not real knowledgeable about our trucks (a '95 and a '97 Blazer). twodoorblazer, could you elaborate a bit more?

My very limited understanding is that these are computer controlled systems that shoot gas into the engine as opposed to a purely mechanical solution found in a carburetor. As to the relative merits of CPI versus SFI, I'm uneducated.

Question, why would the method of fuel injection affect the sound of the engine? I mean, why would one cause more of a roar?

Thanks,
-- recurve

[BlazerLT]

Different heads.