Midget under my hood.

[gmcyukondriver]

Keeps knocking to let him out.

Well, got the truck back from the mechanic, and a couple days later, it's started doing this. It sounds like it's knocking at startup, but only 3-5 times, then it goes away. It's only on startup after it's sat overnight, and even then, it doesn't do it every time. It runs and drives just fine, doesn't knock after that or at higher RPM.

Any ideas?

I'm just wondering why it would do it at startup but not that long. Could it be the computer is retarding the timing?

It's only done it a couple times so far, and it hasn't gotten any worse, I'd just like to figure it out and make it stop.

 

[someotherguy]

What was it at the mechanic for?

Knocking at cold start-up can often be bearings starting to go bad, but it doesn't always mean that. What sounds VERY similar to a start-up rod knock, and also happens on cold starts/very often not on warm starts, is a broken flexplate. It's happened to me and I swore it was a rod knock. Try removing your inspection cover and tap on the flexplate with a wrench. You're listening for a dull/dead sounding kind of thud instead of it ringing back at you. The fact that it's bolted to the torque converter kind of causes it to sound dead-ish anyway, so if you're not sure, you might consider unbolting the torque converter and sliding it back on the trans input shaft so the flexplate is separate from it. It can be very difficult to tell while installed if it's cracked or broken. When I removed mine, the center ring where it bolts to the crank had broken completely all the way around and the flexplate was in two pieces, although it held together while installed. When it's hot the metal expands so the crack tightens up, doesn't knock... By the way, broken flexplate on these engines happens more often than you might think.

Richard

 

[Ruger_556]

What did it go in for? Cheap oil filter combined with heavy weight oil can cause that too... Takes to long for the oil to get where it needs to be.

 

[gmcyukondriver]

It was there for a bad fuel pump. My original ('95 with 200k) took a dump a couple weeks ago. I had just filled the tank the day before and didn't have the time or tools to deal with it on my own.

Thanks, I'll check the flexplate. I'm really hoping that's it. I can't imagine it would be the engine, since it hasn't had any driving issues or codes thrown. Besides, I'm running 91 octane with 1 heat range colder plugs (recommended by Whipple), so that should also help fight pinging.

Oil filter is a Wix with 5w30 Castrol GTX. I changed it less than 2k ago, and it looks good. I'll take another look at the color/level though. Might as well.

 

[someotherguy]

It's also not entirely uncommon for these engines - both the TBI's and Vortecs - to give a couple minor knocks on cold startup, occasionally. Others may disagree but I can recall several I've had like that, that went tens of thousands of miles with the occasional cold start knock and never got worse, never had any other problems.

Richard

 

[Ruger_556]

It's also not entirely uncommon for these engines - both the TBI's and Vortecs - to give a couple minor knocks on cold startup, occasionally. Others may disagree but I can recall several I've had like that, that went tens of thousands of miles with the occasional cold start knock and never got worse, never had any other problems.

Richard

More of a tick than a knock but every TBI truck I've been around makes some noise at cold start.

 

[woody31]

could also be a wrist pin or piston slap..those usually go away with heat after warm up.//

 

[IOWNJUNK]

Just a couple taps on first start every once in a while? I wouldn't worry about it. I've had very few that didn't.

 

[eric.s.t]

ive never experience it... but I know some of the truck around here when its a cold start, sometime it ends up being the valve. Once it gets started and moving, it moves at the right time to stop knocking ...

 

[98_k1500]

Mine has piston slap caused by tight wrist pins like a ***** when its cold outside (40° and below). It lasts about 20-30 seconds until the pistons heat up a tiny bit and move freely on the wrist pins. I just let it idle until they warm a little and the clacking racket goes away. (kinda sounds like a diesel) I have heard that you can crack the pistons if you have this issue and you just crank it and haul a$$, although i have never seen it first hand.