BamaBeach

Hi Chevy Enthusiasts,

I am hopeful that someone can help me help my mechanic figure out what's up on my 1999 Chevy 4.3l Vortec. Here's the issue:

It has an intermittent knock at startup that lasts for about 5-10 seconds. This has been going on for about a year. Last week, I started it up and the knock was much louder and didn't quit. It was so loud (unlike anything before) that I thought if I drove it the motor would blow up... I shut it down and then started it again and it was the same. Scared to drive it and towed it to the shop!

Mechanic (been in business 30 years) checked it out and said that he thought the only thing he thought it could be was the lifters, so we replaced 12 lifters and the gaskets. Was great for the first 4-5 start ups, and now it is knocking again for 5-10 seconds at start up intermittently. Started it about 12 times today and it knocked on about 8 of those start ups.

I've read that knocking is 'normal'... however, it doesn't do it all the time, so have a hard time accepting this as normal. Especially after $800 and no real progress. Confused!

Thanks in advance for advice you might provide so that I can talk with confidence to the mechanic.

SlinkE

Spun bearings could be blocking lubricating holes in the connecting rods. Takes longer for less oil to get to the Pistons?
Just a thought...

oldchevy

My 99 4.3 did the same thing. It was piston slap. Mine never got real bad like yours. I sold it at 175,000 miles and it ran great, jut made a little noise at start up.

BamaBeach

Thank you SlinkE and oldchevy!

I bought it used a little over a year ago after wrecking my 2000 Blazer. There was some sludge in the oil the first time we changed it and have been babying it ever since. She's got 149,000 miles on her right now. Was thinking of changing to synthetic but heard that it wasn't good for the gaskets to change to synthetic this late in the game since it has been running on regular oil. But we just changed those too, so I will most likely go ahead and do synthetic and see how it all plays out.

SlinkE

Keep us posted!
I wouldn't go in suggesting a spun bearing, however. Bottom end work isn't cheap, and a shop you don't know may jump to take you up on it. Let them offer the diagnosis for you to make an educated decision.

BamaBeach

OK... dropped the Chevy back off to the mechanic for the day and of course, she didn't do a thing... no knock, no rattle, no nothing! He said I just needed to give her time to let those lifters get a little oil to them and settle in for a bit... maybe he's right because I am not hearing anything and all is well for the time being.

Thanks for the advice! It is much appreciated!

sledge.impy

The only real time I've heard knock is when replacing my sideways oil filter on an engine after an oil change.. can't really add oil and install.. so it goes in empty with the gasket lubed - and there would be knock on start up. Nice job chevy! (This was on a 2.4L j-body).

But definitely did not last 10 seconds.. maybe 2-3 seconds.

You never said how many miles on the 4.3L?

So does it sound like massive knock on all cylinders or just 1 or so?

I'm not too familiar with vortec 4.3l, but does it require something more than 87 unleaded?

Can you hook it up to a computer scanner and see what's going on?

Natty68

Wife's 98 does the exact same thing........it's a little more pronounced now that it's brutally cold but it's been like that as for a few years. It quiets right down after about 30 seconds.

Ben Allred

I have this problem, I know it's my oil pick up/pump because my oil pressure gauge jumps around indicating a weak oil pump. It's an easy fix unless you ignore it too long.