Unusual noise

[secondchance]

Hi, all ZR1ers,

After cold start in the morning (I have a 94 #256 which I drive daily with 105,000 miles) 1-2 minutes after the start I started to hear a sort of groaning/gritty noise.
At first I thought it was coming from the motor or one of accessory drive/pully but could not identify the source. Another 2-3 minutes and then the noise goes away.
Then I noticed even at warm start (15 minutes or so after shut down) I get the same type of noise.
I am beginning to suspect anti-lock system trying to go through self check sequence. Could someone tell me what generates 30 second or so of squealing type of noise following the start?

[GOLDCYLON]

Well there are normal noises I hear on my daily driver before and after starting it up are:

1. The Fuel Pumps will whurr when turing the key before starting the car
2. Chain tensoner rattle for about 3 secs until the oil is pushed up from the pan
3. The Air Pump runs as long as a minute, Depends how cold it is outside
4. The ABS self check sequence after backing and then proceeding forward a few feet, The ABS light will also flicker

So if these are not the noises you expect maybe a alternator bearing or ?

[tccrab]

There is a sequence of noises as described by our Cycloptic friend.

1. Key on, fuel pumps pressurize the fuel system
2. Once engine starts, the secondaries vacuum pump fires up for about 30-50 seconds
3. The SMOG air pump fires up and runs for 2 or 3 minutes
4. The ZF6 makes it's signature noise until the clutch is depressed.

Try depressing the clutch and see if the noise abates. Worn pilot bearings and throwout bearings can and do makes weird noises.

If it's coming from under the hood, items 2 & 3 might be worth looking into.

Where are you located? I'm sure one of the boys wouldn't mind coming by to take a listen and help you with the diagnosis.

TomC
"Crabs"

[Jagdpanzer]

I'm over in Fairfax, VA and would be glad to have a look at it.

[ZR1Vette]

Sometimes on the GM mag clutch for the AC compressor will make funky noises when AC is off (thus clutch not engaged)... try turning on the AC and see is noise ceases... just one option of many already posted

[QB93Z]

Does the noise you hear occur with the car sitting still or as you start to drive?

I am sure that Phil (Jagdpanzer) and Michael (ZR1Vette) will give you some expert advice. If you need any other help, post again or PM me. There are a lot of knowledgable ZR-1 owners nearby to you.

Also, if you want to be informed about the activities of the ZR-1 owners and get togethers in the Maryland and northern VA area, PM me and I will add you to our list.

Jim

[secondchance]

Wow!
I know ZR1 guys are tight-knit bunch but what a response!
Now that you guys have pointed out, most likely in sequence;
1. Throwout bearins.
2. Possible air pump.
3. AC clutch.
4. Possible air pump.

She has been idling a little high, so during the weekend I will spend sometime and dismantle idle solenoid and clean it out. I will try to locate the noise at the same time.

Noise ocuurs with engine running whether stationary or while moving.

Thanks guys.

[QB93Z]

Wow!
I know ZR1 guys are tight-knit bunch but what a response!
Now that you guys have pointed out, most likely in sequence;
1. Throwout bearins.
2. Possible air pump.
3. AC clutch.
4. Possible air pump.

She has been idling a little high, so during the weekend I will spend sometime and dismantle idle solenoid and clean it out. I will try to locate the noise at the same time.

Noise ocuurs with engine running whether stationary or while moving.

Thanks guys.

It is easy to narrow down that list:

1. Throwout bearing: the noise will only occur when the clutch pedal is pushed in.

2. Air Pump: Raise the hood. The air pump is in the well in front of the left front tire. Put your hand on it and see if it is vibrating when you hear the noise.

3. AC Clutch: When you have the noise, turn off the AC system (OFF button on the dash).

Another posibility is the AC blower fan. Turning the AC on and off and/or changing the fan speed should affect the noise if that is it.

A high idle may also be caused by a vacuum leak.

Good luck. Let us know if we can help.

Jim

[LT5-Lee]

I have had my serpentine belt stretch out so far it 's backside was slapping itself. Of course the A/C exaggerated it and the tell tale signs was a lot of pulverized rubber particles under the air horn area. I am actually using one size smaller belt than OEM now.

[secondchance]

Thanks. for all your input.
If and when I find what the culprit was I will repost for record sake.

Thanks.