5.0 engine knock on start up only

[Goat67400]

When I first start my 1994 GMC C1500 5.0 there are three knocks just prior to acceleration after start. It then quits and while driving or setting at a red light there are no knocking sounds.

After I stop and kill the engine and do what ever and then upon return sometime later and start it there are no knocks whatsoever!

Please help...

 

[Jeepwalker]

Sounds like classic piston slap the way you describe it. That's wasnt uncommon back in the day.

I knew a guy who's like 86 suburban did that every morning and he HATED it. He felt subconscious about it and would volunteer every time, it was just piston slap, "Kevin *** (best mechanic at the chevy dealer) looked it all over for me ...they all do that." .....of which I would always roll my eyes and make some statement if he had tripple-A or I didn't have my good walking shoes on... or maybe better get an umbrella. LOL His knocked after start-up for ever and never let go. And he towed a lot with it too.

 

[tayto]

remove the cheap oil filter and put a quality one on. pretty sure there was a TSB about this problem back in the early 90s

 

[Goat67400]

remove the cheap oil filter and put a quality one on. pretty sure there was a TSB about this problem back in the early 90s

Its due for an oil change now.

Don't know if it has anything with the knocks just starting but I just had tune up done at a reputable garage. they replace distributor cap, rotor, wires and reset timing. Your thoughts on that?

 

[Goat67400]

remove the cheap oil filter and put a quality one on. pretty sure there was a TSB about this problem back in the early 90s

Sounds like classic piston slap the way you describe it. That's wasnt uncommon back in the day.

I knew a guy who's like 86 suburban did that every morning and he HATED it. He felt subconscious about it and would volunteer every time, it was just piston slap, "Kevin *** (best mechanic at the chevy dealer) looked it all over for me ...they all do that." .....of which I would always roll my eyes and make some statement if he had tripple-A or I didn't have my good walking shoes on... or maybe better get an umbrella. LOL His knocked after start-up for ever and never let go. And he towed a lot with it too.

Its due for an oil change now.

Don't know if it has anything with the knocks just starting but I just had tune up done at a reputable garage. they replace distributor cap, rotor, wires and reset timing. Your thoughts on that?

 

[someotherguy]

Sometimes this can be a cracked flexplate (auto transmission.) They crack around the crank flange.

Richard

 

[Goat67400]

Its due for an oil change now.

Don't know if it has anything with the knocks just starting but I just had tune up done at a reputable garage. they replace distributor cap, rotor, wires and reset timing. Your thoughts on that?

 

[someotherguy]

Very unlikely the recent work has anything to do with it.

I've got some recommendations on narrowing down the source of the noise but if you're having a shop do the tune-up, no offense intended, it's probably gonna be more involved than you'll want to do yourself.

If you believe the shop is truly reputable, time to have them check it out. If it's just the flexplate that's not a very expensive job, just a bit of labor as the transmission has to be pulled away from the engine to get in there and replace it.

If it's bearing wear, well that's gonna be a much bigger repair bill.

Richard

 

[TonyM]

Sometimes this can be a cracked flexplate (auto transmission.) They crack around the crank flange.

Richard

This

 

[GrimsterGMC]

I second the oil filter internal seal not preventing the oil from draining back when sitting. Mine started doing it after an oil change and the oil pressure would take a little longer to come up resulting in a couple of knocks when it first fired. Mine came right after a week or two but may last longer.