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What is this engine tapping noise?
I have a 93 Chevy Blazer, 4.3 Vortec, Vin "W" (Central port injection). It's a balance shaft engine. The engine is making a tapping noise, sounds exactly like someone tapping the tip of a pencil against a table. Most of the time it's steady, but it gets louder and softer (sometimes it entirely disappears for a few seconds). Also, sometimes it turns into a double tap, like someone tapping both ends of a pencil on the table. When it does that, the sound seems to move towards the right side.
The tap seems, for the most part, to be in time with one of the cylinders. I've read that pulling off a spark plug wire will make the sound change if it's piston slap in that cylinder. I tried it for each cylinder, got no change but on the #1 cylinder I was getting shocked in time with the tapping sound.
The sound seems to be coming from low on the engine, it is definitely not in the valve covers. When I listen there, I can hear the tappets, they're quiet and smooth. It's also in the front of the engine, right around the crank pulley, not back in the oil pan. It is not an engine accessory, I've tried running it with the serpentine belt off. The crank pulley has some visible wobble when the engine runs.
Other info: The oil pressure reads high, tops out the gauge most of the time, but fluctuates (sometimes comes down to 30) once the engine is completely warm. I'm running 10w40, should have used 5w30. I did a motor flush before the last oil change, the oil appears perfectly clean. There is no significant oil leak (engine is dirty, no drips). The engine is running fine, not missing. The noise does get faster and louder with rpms.
So, does anybody out there know what this is?
6 Answers
- Anonymous1 decade agoFavorite Answer
I think its a knock more than a tap. My bet is the "Main Bearing" in the bottom of the block GM's are or at least used to be infamous for that. I think the bottom end of the motor will need to be rebuilt in order to relieve the noise. Try some "Marvels Mystery Oil" it should quit it down for a couple days. I drove my blazer that way for over a year but sold it before it went out for the record i told him about the problem.
Source(s): same problem with blazer before as well as chevy truck - Anonymous1 decade ago
If the problem was big end bearings or crank, you would here the knocking if you slugged the motor in high gear, forcing the crank to bounce around.
You could try a mechanics Stethoscope or long handle screwdriver or similar. Put this against the area where the noise is and the other end against your ear.(don't get caught in fan blades, pulleys etc) You can usually isolate the source to a specific location on the motor.If the problem is coming from the main pulley ( the wobbling one) it may just be a harmonic balance problem or similar.
good luck?
- Anonymous5 years ago
If the oil light came on with the oil level full it's possible the oil pump is not working properly, if at all. The car will still run, but you will do major damage if you do run it without oil. Check the oil filter and make sure it's not clogged. That will also cause a low oil pressure situation and cause the engine knock. If that's fine then have it towed to a mechanic. Do not drive the car or you will likely damage the engine beyond repair.
- 1 decade ago
Its just a clip to a hose is loose and the hose is tapping. or similar. Otherwise you would have more symptoms. Open the hood up and listen again,
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- Anonymous1 decade ago
try flushing the radiator