Grinding Noise Under Dash

[tcschweitzer]

I have a 96 s10 blazer 4x4. I have a strange noise coming from what seems like behind the dashboard. I would describe the noise as a grinding/clicking noise. Kinda sounds like little plastic gears grinding together. The sound is RMP dependant; it gets worse as you lower the idling rpm (engaging the breaks or turning the wheel) and goes away as you goose the throttle and seems to happen only in colder temperatures (happens in all gears). I am 99.9% sure it is not a major mechanical noise, rather an electrical noise. My first instinct was to replace the distributor cap; however, little did I know the 4.3 in distributorless. The next thing I tried was to replace all the vacuum lines. Didn't make the slightest difference, but what I concluded was that the noise has to be coming from inside the dashboard - inside the car. This very noticable and rather annoying noise cannot be heard from the engine compartment. The noise has been there ever since i purchased the vehicle three years ago. Any suggestions??? Everything in the car is mechanically sound.

[muzzy1maniac]

Welcome to the forum...

Blazers are distributerless? I wish someone told me that sooner!!


You never said if the noise is constant or not. Also do you thing the noise is going away with the acceleration or just being covered up by the additional noise?

[muddog321]

The dist is at the rear of the engine and has a cap/rotor - follow the plug wires. That noise needs more definition - could be almost anything coming fom behind, below, etc. PCV can click rpm dependant. Heater core noises. Anyone know about the speedometer, any drive gear back there on a 96.

[rlith]

I wish the 4.3 was distributorless! Would jut have to change coil packs then! LOL. Unfortunatly they do have distributors and thy are located at the rear of the engine behind the intake manifold as stated above.

[tcschweitzer]

Noise goes away with acceleration completely and usually goes away after the engine warm up, unless it's below zero outside. I wouldn't doubt if it has something to do with the heater core - i've suspected a problem there for some time. It seems I get air in the system every once in a while (makes a water rushing noise), but topping the coolant off fixed the problem. I know heater core problems are common in my year blazer. Maybe these two problems are related - i've just never heard anything like it.

[rlith]

Well if it is the heater core, then it would gurgle, not grind. That said, replace out your stock cap with something else (most reccomend stant) and lt it bleed properly. Are you using regular green or dex-crap antifreeze? Considering the age of the vehicle you should probably have a profession full acid flush done to the system.

[tcschweitzer]

Yeah, I know the gurgling noise well, i fixed that by adding coolant straight into the radiator. THis sound is totally different, it's a definite grinding. I guess i should have metioned this, but the whole engine is a jasper rebuilt and was installed about 20,000 miles ago. New radiator was installed with the proper coolant (not the dex crap lol) and whole system flushed. To my knowledge the heater core is original, but I havnt had any overheating or hvac problems. The only reason I would venture to say these components may be related is because of the grinding noise is temperature dependent. Another tidbit of info - this is apparently not a common blazer problem; i've scoured the internet for hours looking for people with similair issues. Found none.

[Markgc]

It's not your speedometer or rev counter is it? Maybe speedo


Mark

[tcschweitzer]

Oh, by the way. I apologize for the false statement about the distributorless ignition. The ignition does indeed have a distributor. Only the 2.2l is distributorless. My mistake; thats what I get for believing everything I read, lol.

[tcschweitzer]

Its not the speedo, and I don't have a tach, lol. The sound seems to be deeper inside the dash, almost like its coming from behind the kickpanel. I'll tell you, i've driven alot of cars and heard alot of noises and this one definately has me dumbfounded.

[rlith]

Originally Posted by Markgc

It's not your speedometer or rev counter is it? Maybe speedo


Mark

88 and up speedos are electronic, there is no speedo cable

[rlith]

Originally Posted by tcschweitzer

Its not the speedo, and I don't have a tach, lol. The sound seems to be deeper inside the dash, almost like its coming from behind the kickpanel. I'll tell you, i've driven alot of cars and heard alot of noises and this one definately has me dumbfounded.

Hmm, I wonder if it's you hvac fan... Try turning off your heat and your hvac completely and see if it goes away.

[tcschweitzer]

tried it, lol. Has nothing to do with it. I've had fan problems before, its behind the glovebox and makes more of a clipping noise. This is more of a mute RPM and temperature dependant grinding noise. It sounds electrical, i guess thats the best way i can put it. I know i used alot of adjectives but bare with me, lol.

[muddog321]

So, did you put your hand on the PCV when at idle and the noise is there?
If the throttle cable is against it sounds like in the dash! Most cables have a broken plastic clip that secures them to the intake away from the PCV. Also a broken rubber "L" on PCV to intake may cause problems. Till you check this don't laugh at it - 2 of mine did it after intakes.

[tcschweitzer]

Wow, that sounds right on. I did notice the noise changes pitch as i feather the throttle. I'll check that right away. If it was the PCV, wouldnt i get a check engine light?