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Discussion Starter · #1 ·
I have a 1968 / 289 c4 that I just noticed a tappin or knocking sound from the engine area. Sounds close to the lower left rear of engine bay. Could it be the gas/fuel that I just put in? Or something a bit more major?
 

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If it only happens when the engine is under a load, then it could be something that can be fixed by a timing adjustment or different gasoline.

If it happens at idle with car in neutral or park then you have an internal issue. That might be fixed by lifter adjustment or replacement, or it could be a main or rod bearing failing.

You should be able to tell what part of the engine the sound is coming from, and that deduction will help your troubleshooting.

if you are sure it’s a lower engine noise I would drop the pan and check the bearings before the damage gets worse, ie more expensive.

Z
 

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If it just happened with new gas run the tank and refill with 93

Also check for exhust leak
 

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Discussion Starter · #6 ·
If it only happens when the engine is under a load, then it could be something that can be fixed by a timing adjustment or different gasoline.

If it happens at idle with car in neutral or park then you have an internal issue. That might be fixed by lifter adjustment or replacement, or it could be a main or rod bearing failing.

You should be able to tell what part of the engine the sound is coming from, and that deduction will help your troubleshooting.

if you are sure it’s a lower engine noise I would drop the pan and check the bearings before the damage gets worse, ie more expensive.

Z
ok thanks for the info. I just pick the car up last weekend it was restored I’m not sure if this is a separate issue or not but after washing it today I noticed that it’s harder to start from the standpoint of pumping the gas and pushing the pedal to the floor now as opposed to when I first brought it home just having to pump the gas a few times and starting right away now it’s not starting right away and hearing this knocking/pinging sound now could be totally separate issues but just wondering
 

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ok thanks for the info. I just pick the car up last weekend it was restored I’m not sure if this is a separate issue or not but after washing it today I noticed that it’s harder to start from the standpoint of pumping the gas and pushing the pedal to the floor now as opposed to when I first brought it home just having to pump the gas a few times and starting right away now it’s not starting right away and hearing this knocking/pinging sound now could be totally separate issues but just wondering
Ok, What do you know about its "state tune"?
 

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Discussion Starter · #8 ·
ok thanks for the info. I just pick the car up last weekend it was restored I’m not sure if this is a separate issue or not but after washing it today I noticed that it’s harder to start from the standpoint of pumping the gas and pushing the pedal to the floor now as opposed to when I first brought it home just having to pump the gas a few times and starting right away now it’s not starting right away and hearing this knocking/pinging sound now could be totally separate issues but just wondering
I don’t hear it at idle. I do hear it under load or when accelerating or over 40 miles an hour. Thinking it may be the gasoline that I put in today or water somehow after washing it getting in the carburetor? not sure.
Ok, What do you know about its "state tune"?
I really don’t know
 

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Cheap gas + timing advanced too far = hard starting and ping under light load. Could be an exhaust leak that presents more under load, too.
 

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I don’t hear it at idle. I do hear it under load or when accelerating or over 40 miles an hour. Thinking it may be the gasoline that I put in today or water somehow after washing it getting in the carburetor? not sure.

I really don’t know
If you "don't know", then get out your shop manual, a notebook, gather a few tools and start tuning and documenting. Then, you will know!
Perhaps, you now know, when washing the engine bay, remove the AC and cover the carb, also, the distributor too. pretty much all else is OK(?) as long as you're not "drenching" it. I like to use my air compressor afterwards.
 

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Check for loose spark plugs.
 

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Converter or flex plate bolts can be a source for knocking as well as motor and transmission mounts.
Spark knock, rod knock, driveline knock have a distinctive sound. Is there a frequency or rhythm to the knock?
 

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Discussion Starter · #13 ·
Interesting, if I had to describe it better maybe like a can of spray paint, ball rattling around without the paint.. does that help. Lol. Only when exceeding 40mph or higher mostly up hill
 

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Could be pre ignition - which is caused by advanced timing (too advanced) or the octane value of the gas you are using is too low - this is only my two cents. Do you know your compression ratio of your engine?
 

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Discussion Starter · #15 ·
No, I need to run a compression test. I just picked up the car last weekend and am now noticing the noise. I’m hoping it’s the fuel. Gonna try running some high grade this week and see how that works.
 

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Sounds like pre-ignition pinging. Take a 1/2" wrench with you on a drive. Retard your timing just a bit and test. Back off until the pinging stops.
 
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