michrobi

Hi There,

I purchased a 96 CE LT4 on May 3rd with 19214 miles. Seemed perfect, other than a couple of issues. The 'ol HVAC doesn't blow out the front vents (defrost and floor only) issue that is well known. And the wiper fluid doesn't spray. Other than those 2 things, perfect.

I've been driving it to and from work (41.6 miles round trip per day) and a few weeks ago I first noticed a very difficult to hear knock, or click coming from the car. Most noticeable when in a one lane ramp going slow or idle right next to a concrete barrier that reflects the car's sounds right into my window. At first it was so quiet, I just chalked it up to AC compressor clicking that is not uncommon.

Well, it's been getting progressively louder. So, what do you think it is? Thanks in advance!



-michrobi

billschroeder5842

Sorry, I missed it. Sounds like a smooth LT4 to me

michrobi

Yeah that video is far less clear than I was hoping. It's most obvious when I move the camera to the underside of the car. Crappy smartphone mic.

cv67

injectors can tick making you think something is wrong they all do it some more than others.

michrobi

There are lots of noises and I think my language is less that descriptive. It really is a knock and not one of the clicks that are clicking around. It's really hard to distinguish on the video, but super obnoxious to the ear. The sound makes me think of a 5 gal bucket being tapped with a rock. So imagine the sound holding a bucket in one hand and thunking a small rock on it would make. That's the sound I'm worried about.

70ZZ3 96LT4

My original owner 1996 LT4 with about 50K on it now with the engine at idle the six speed no gears selected, clutch not depressed makes a different noise if I am not in the car, no problem for me to be concerned about. Never raced or abused in 21 years.

DGXR

I hear the knock but on the video it seems mild, not too serious, especially if it doesn't get worse with a load or RPMs. Hard to tell from a video though.

The high-pitched whine noise would irritate me to no end.

cv67

if its a 6 speed it could be your dual mass flywheel/TB they all can make a little, just the way they are;does it get quieter if the clutch is pushed in?

Go put some miles on it

JimLentz

LT4, it must have a ZF6.

michrobi

No, the clutch position has no effect on the knock. I have revved the motor a little at idle to see if it gets louder or faster, but I can't detect it above idle. It either goes away or is absorbed by the engine breathing at above idle. It's much less pronounced when cold.

michrobi

Here is with the car running, sitting in it while it's right against a brick wall to reflect the sound. I think this is a better clip.



Here is me trying to make the sound so you can see how uncoordinated I am... Also, you can hear the timing and approximate tone of the sound in question.



Any better?

tlong

Exhaust manifold? Get a wooden dowel about 2 feet lomg and stick it around the motor on your ear. Valve adjudtment? Sounds like a lifter maybe. Determier top or bottom end for now with dowel or big screwdriver or if you must a stethescope.

gdl2165

I think it sounds like an exhaust leak too, maybe a cracked exhaust manifold. Get a piece of rubber tubing, like heater hose, about three feet long. Hold one end to your ear and use the other end to poke around in the vicinity where you think the sound is coming from.

RIC96

I heard it on the first video. Are you sure the frequency doesn't increase as the rpms increase?

Cool Runnings

Try using a very large screwdriver with the handle to your ear and the other end placed to different parts of the engine to locate where the noise is coming from.

michrobi

I think the frequency does adjust to the RPMs, but I can only detect it for a second. Once I clear 1000 RPM the sound disappears or I just can't hear it above the engine intake/exhaust . I'll dig my tube steth up and sniff around tonight.

It sounds like I need to focus around...

1. The valve covers for a rocker
2. The Fuel injectors
3. The manifolds

bac22

Not sure it's related but there was a recall for the rocker arm on some LT4's

http://www.corvetteactioncenter.com/...eated-516.html

michrobi

Looks like mine isn't included T5113xxx

michrobi

I tried Octane booster. No improvement.

Changed the oil and filter. I think I detected a tiny improvement.

A really good tuner that works with a ton of Corvettes here in Seattle listened to it today. He said it was so minor that if it was his he'd put a zinc oil supplement in and "drive the **** out of it". So I poured a bottle of Lucas oil additive Zinc plus in there and drove it home. The sound is almost all gone now. I doubt I would notice it if I wasn't looking for it.

Never the less, I need to get into that valve cover and see what's really going on. So I'm shopping for rocker arms. I didn't turn up any NOS rockers for the LT4, but what do you think about swapping the 10mm studs out for 3/8" and these http://www.gmperformancemotor.com/parts/19210729.html ?

Fiberbundle

Who is your tuner in Seattle? Always looking for more options than the few that are around.