Timing and knock issue.

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Sep 10, 2007 | 11:32 PM

Dads90

Thread Starter

Burning Brakes

Joined: Oct 2004

Posts: 898

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From: Pearland Texas

Timing and knock issue.

I have jacked with the timing for months trying to retard a knock issue. I have started this thread hoping others might join in with my issue. The knock has occured when the car is warm and idling. I notice that when the knock occurs the car is idling a little rough, I can feel the knock thru my stick shift, and hear it (kachunk,kachunk)every 8-10 seconds. It used to get bad like every 2-4 seconds, I since replace fuel injectors, distrib, wires, and upon advice from our company mechanic move the timing to 10* BDC and actually seemed to help. Due to an idle issue, under cool conditions, which has been resolved with members help, I moved the timing back to 6* BDC. I noticed the knock is reoccuring. Its funny it doesn't occur but only occasionally. Its a faint kachunk sound and one every 10 seconds or so. Now, if I turn on the AC it doesn't seem to occur. I'm running a 8.5* BDC now and I will monitor the sound, heck I don't even listen to the radio, just listen for the knock when stopped.

Sep 11, 2007 | 01:10 AM

ultraviolet70

Drifting

Joined: Dec 2005

Posts: 1,313

Likes: 2

From: High Ridge Missouri

I'm gonna guess the car's a six speed. Since your feeling it through the shifter I'm gonna think you might have a failing D.M. flywheel.

Sep 12, 2007 | 11:37 PM

Dads90

Thread Starter

Burning Brakes

Joined: Oct 2004

Posts: 898

Likes: 1

From: Pearland Texas

ttt

Sep 13, 2007 | 07:41 PM

CFI-EFI

Race Director

Joined: Sep 2000

Posts: 17,298

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From: The Top of Utah

Your description of the noise is not that of spark knock or detonation. Use a stethoscope or a big screw driver to your ear to listen all around the engine in search of the source of the noise.

RACE ON!!!

Sep 13, 2007 | 11:18 PM

Dads90

Thread Starter

Burning Brakes

Joined: Oct 2004

Posts: 898

Likes: 1

From: Pearland Texas

Quote:

Originally Posted by CFI-EFI

Wouldn't the noise be a constent ? I can go a couple of days without a sound. I noticed that the idle speed being around 725 rpm the sound has reocurred. When it was around 1000 rpm the sound never was heard. I will listen with a screwdriver this weekend.

Sep 14, 2007 | 10:29 AM

byebyeL98

Safety Car

Joined: Sep 2003

Posts: 3,599

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From: Orange County NY

St. Jude Donor '10-'11-'12-'13

Quote:

Originally Posted by CFI-EFI

It sounds as if something is not bolted up tightly. I think the timing / rpm changes are just masking the problem by putting the engine in a state where the "knocking sound" isn't happening. By turning on the A/C, idle speed is added & timing changes (with the additional load), so the sound is once again masked.

I'd set the timing correctly, turn off the A/C, and let the noise occur so you can find it. Failing DM flywheel? Loose engine mount? Loose starter? Something is not tight...

Sep 14, 2007 | 11:12 AM

CFI-EFI

Race Director

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From: The Top of Utah

Quote:

Originally Posted by Dads90

Wouldn't the noise be a constent ?

I would expect a spark knock to be consistent, but I wouldn't expect a spark knock or detonation too occur at a steady low speed or at idle under no load. Plus adding timing will aggravate a spark knock problem, not alleviate it. It sounds to me as though you have something that is rattling or vibrating and that the different idle speeds set up varying harmonics that change when you do or don't hear it.

RACE ON!!!

Sep 14, 2007 | 11:30 PM

Dads90

Thread Starter

Burning Brakes

Joined: Oct 2004

Posts: 898

Likes: 1

From: Pearland Texas

I did notice the belt tensioner bounces when the knocking occurs. I thought it was making the noise so it was replaace with a new one. The noise isn't as prevelant. I think I will go back to 6* BDC and listen closely. Thanks guys I will be experimenting this weekend and will post back.