Graphicsplus123

Once again hello all,

Ok so Ive been getting this horrible knocking sound which sounded like it was coming from underneath. Sounds like bolts rattle around in a can. I jacked it and did the stethoscope on the oil pan, flexplate cover and cats. Cant seem to pinpoint it. Definitely not on top.

So my Alternator went out and per a suggestion from my brother (backyard mechanic) told me to remove the belt and before installing the new alt. and belt, give the engine a run without the belt.

Ok so I did this and removed the belt and water temp sensor plug on pump. Started it up and noise seems to be gone. Further troubleshooting I plug the sensor back in to pump and noise returns but not as loud.

How to proceed from this point? Think its the pump, MAF?


HELP!!!

Thanks

pcolt94

The sensor in the water pump drives the digital temp gauge and the PCM. The sensor is a major input to engine performance mainly fuel/air ratio. Usually at an idle if the sensor is disconnected, the engine goes so rich it stalls. It's hard to make the connection or jump that the sensor will cause or stop a noise.

I would first check really good all engine accessories as well as the balancer.

Sure it's from the engine? Check out the air pump and the ABS pump to see if anything strange is really going on.

s carter

Is it a Automatic or a Manual trans? Many new to the Corvette family are kind of unaware that the ZF 6 speed is kind of a noisy Transmission. I suspect you have a Automatic because you call out having a Flex-plate cover,
so with that said if you do have a 6 speed does it go away with the clutch in and in gear?

Does it go away with raising Idle just off of base idle.

jv9999

What's the oil pressure at a hot idle?

Graphicsplus123

Its an automatic and noise doesn't change when put in gear. I listened to an Lt1 with rod knock the other day and mine doesn't sound the same. It doesn't really get faster with rpm at least not as fast as the engine rpm.

Oil pressure hot at idle is around 20-22 and cold around 60-70.

It was only doing it when cold and would go away but now all the time. With the belt off it seems less noisy but still can hear it a little. Putting the new alt and belt on today and I'll see what I get.

Where is the air pump or abs pump?

thanks for the responses.

s carter

Since the water pump is driven off of the cam could it possibly be the pump or is it farther back, it sounds almost like a small carbon chunk.
We need know a little better were

After thought is the coolant level good, may want to Crack the bleeder on top of water pump just in case you have some cavitation going on

pcolt94

Air pump is in the front left fender by horn and relays mounted low. Runs for 2 minutes when engine is started and cold.

ABS pump runs for few seconds when you first move over 4 mph for the ABS test. It's a onetime shot after starting up and moving and is mounted in the compartment behind the driver's seat. It should not consistently run. Sounds like a ratchet for the test.

Graphicsplus123

Update,

I finally got the new alt put in. It's rare that things should be simple. When I removed the old alt, the volt reg. pigtail fell apart so I had to find a new one. Slim pickings down here in paradise. I also purchased a new belt but of course I couldn't get it to fit. I wound up putting the old back on temporarily until I can find the correct one?
The new one looked right but it was just a fraction short and it would not go on.

I checked the air pump and it isn't the sound I was hearing. That is more of a high pitch whine that lasts a minute or so when started. After getting it all back together it hasn't made the knocking noise yet but I haven't run it for any length of time. Kind of odd as it was making it all of the time before hand, even on start up so after this storm passes us I am going to get it over to a mechanic.

Thanks and I'll update as I find out more.

pcolt94

In installing a new belt in the past I have found it to be and extremely tight fit. I remember I had to pull the tensioneer all the way and then push the belt over the A/C compressor. It almost did feel like the belt was wrong but just a tight fit. I think I had to work the belt over the pulley with a screwdriver which I did not like doing but did not have the strength in my fingers to pull it across the pulley.

Graphicsplus123

Yea I thought of that but after an hour of struggling decided to return the belt and they happen to have another option that was just a fraction bigger. We don't have many options down in the Keys so I gave the new one a shot and it was perfect. I know the ZR1 has a different belt size but that is a few inches bigger than the regular so not sure What they gave me the first time but keeping the part number for the second on file for sure.

The one that fit is a NAPA Micro-V #060675. The one that was just a hair short was # 060670. the 670 is the one that comes up as the correct replacement and not sure where the 675 comes into play but it worked.