Knocking

[Schurkey]

The next time the engine is stone cold, before starting it, temporarily remove the #1 spark plug wire...

...Don't run the engine more than absolutely necessary to prove to yourself that the sound has/has not been affected.

Don't merely disconnect the plug wire. Make sure the spark is grounded or the spark voltage goes sky-high, and that's really hard on the ignition coil, and all the insulation in the ignition system secondary circuit.

A jumper-wire from the spark plug end of the plug wire, to ground would be fine. Alternately, poke a small, blunted, greased finishing nail BETWEEN the plug wire and the distributor cap boot, until the nail touches the metal plug-wire terminal. Then ground the nail with the jumper wire. DON'T puncture the insulation.

Photo shows all eight, you'd only need one.

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[Road Trip]

Don't merely disconnect the plug wire. Make sure the spark is grounded or the spark voltage goes sky-high, and that's really hard on the ignition coil, and all the insulation in the ignition system secondary circuit.

A jumper-wire from the spark plug end of the plug wire, to ground would be fine. Alternately, poke a small, blunted, greased finishing nail BETWEEN the plug wire and the distributor cap boot, until the nail touches the metal plug-wire terminal. Then ground the nail with the jumper wire. DON'T puncture the insulation.

Photo shows all eight, you'd only need one.

You must be registered for see images attach

Sage advice. The more I learn about the specifics of the GMT400 era ignition
systems, the more it's apparent that it has enough power to actually wound itself
when everything isn't working perfectly. (Instead of just causing misfires as the
components age out, the system tears itself up too at the same time.)

Given this, if we are either troubleshooting the ignition system itself -or- temporarily
modifying the ignition system to troubleshoot something else (like the cold
start noise above) we need to actively manage the high energy discharges.

Shrurkey's recommendation is spot on - discharging to ground via his method
avoids the max voltage stress induced when the system is forced to fire into
a open circuit -- this open could cause up to a 40Kv rise in voltage, and that's
a lot of energy looking for any possible path to ground.

Good call. We're a long way from a stock points system in a pre-emissions '67 Nova.

Cheers --

 

[Scooterwrench]

HEI will create a 2" long lightning bolt out of the side of a bad wire,ask me how I know.

 

[91babyblue]

My ‘98 factory 5.7 makes a knocking sound after a cold start. I do have a good bit of engine experience but I haven’t come across anything quite like this. It starts the knock about 3-4 seconds after the start and continues for about 20 seconds then goes away. It doesn’t seem like a lifter because the sound is deeper but it isn’t a rod. A rod would knock within the block but this knock is located on the left front up close to the head. I’m wondering about carbon but I’ve tried full-throttle runs without any smoke plus it doesn’t change anything. ‍

Mine does the exact same thing. I got 1991 350 with 150000 km. It does exact same. Thag deep inside thing. I run 10/30 regular. I did switch to 5/30 regular oil. I don’t drive it on winter. Truck in nice shape. It’s parked in garage. I start it sometimes in winter. It does the same exact thing as yours. It stops after a bit. I experimented. I plug it in and let block heater heat it up. Lo and behold , no sound. I did the same today , I plugged it in for 20 minutes. I started it. Barely no sound. Then it warms up Rolls like a top. I was thinking of putting amsoil oil like you got to see if it would still do it ?? My engine leaks a bit here Snd there. I didn’t want waterfalls of oil coming out of it. So I left the fossil oil in it. If rolls like a too but…. That cold start. Try to plug yours in , and see if it stops that deep unknown knock. Let me know. Thx. That’s my input. Everyone else has great ideas too.

 

[GMTMark]

Unfortunately mine doesn’t have a block heater. I guess it’s because I live in the south. I don’t think I’ve ever seen one except in a diesel. However I have noticed it being louder in cold weather and I have heard of it happening in other trucks like ours. Thanks for the reply.

 

[91babyblue]

My ‘98 factory 5.7 makes a knocking sound after a cold start. I do have a good bit of engine experience but I haven’t come across anything quite like this. It starts the knock about 3-4 seconds after the start and continues for about 20 seconds then goes away. It doesn’t seem like a lifter because the sound is deeper but it isn’t a rod. A rod would knock within the block but this knock is located on the left front up close to the head. I’m wondering about carbon but I’ve tried full-throttle runs without any smoke plus it doesn’t change anything. ‍

Long story. I will be waiting till summer temperatures. And see if that knock is still there . My two bits.

 

[91babyblue]

My ‘98 factory 5.7 makes a knocking sound after a cold start. I do have a good bit of engine experience but I haven’t come across anything quite like this. It starts the knock about 3-4 seconds after the start and continues for about 20 seconds then goes away. It doesn’t seem like a lifter because the sound is deeper but it isn’t a rod. A rod would knock within the block but this knock is located on the left front up close to the head. I’m wondering about carbon but I’ve tried full-throttle runs without any smoke plus it doesn’t change anything. ‍

I hear that sound on both sides though. Up front on drivers side. And on passengers side kind of in back. ?? Wanted to clarify. But when I plug it in. No sound. Cold engine.

 

[91babyblue]

Unfortunately mine doesn’t have a block heater. I guess it’s because I live in the south. I don’t think I’ve ever seen one except in a diesel. However I have noticed it being louder in cold weather and I have heard of it happening in other trucks like ours. Thanks for the reply.

Just in case. Borrow an oil pan heater. Might do the same job as a block heater. Not sure. I was going to try that when I get one.

 

[91babyblue]

Just in case. Borrow an oil pan heater. Might do the same job as a block heater. Not sure. I was going to try that when I get one.

They s add re just magnet on there

 

[91babyblue]

They s add re just magnet on there

They just magnet on there. Keeps oil warm. I was going to try. I kniw mg engine ran king all 3 years I had it ,but just noticed this winter thag strange noise