Midget under my hood.

[88GMCtruck]

in the 200k I had the TBI350 in my 88 it never made any weird startup sounds..... My 4.8L LS on the other hand... it piston slaps like a **** on cold startup.

 

[bluex]

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.

Mine has done this for 3 yrs an almost 50k miles now. I've even had people ask me if its a diesel on really cold mornings. Under 30* it takes a few minutes for mine to go away. I don't usually let it idle more than a minute. I go easy on the throttle an keep it under 2000 RPMs until it quiets up. It has almost 273k on it now. Our 02 suburban does it as well at 156k miles...

IMO if it goes away its probably piston slap an there's really no cure for it without a rebuild. Run it till it goes, I personally have never seen a rod knock that goes away...

 

[98_k1500]

IMO if it goes away its probably piston slap an there's really no cure for it without a rebuild. Run it till it goes, I personally have never seen a rod knock that goes away...

Right on, Maybe a lifter, but more commonly its piston slap on these trucks. Rod knock can be identified by revving the engine to about 2500 rpm in neutral. If its a rod bearing, you will know immediately. Like i said, its caused by the pistons fitting too tightly to the wrist pins, and when the rod moves back and fourth, it slaps the piston against the side of the cylinder. As the piston heats up and expands, it moves smoothly and no longer slaps the piston side to side in the cylinder.

 

[someotherguy]

As long as you are maintaining at least the bare minimum oil pressure as indicated by GM for the TBI small block - 6 psi at 1000 RPM, 18 @ 2000, 24 @ 4000, etc. I would not sweat it. Instead of the "10 psi for every 1,000 rpm" rule of thumb, the figures I posted are straight from GM. Obviously, seeing more than the minimum is better, but those are the figures.

Richard

 

[scoob8000]

Watch your oil pressure after you start it. Does it go away when the PSI builds?

 

[Hood93z]

Mine does this too 94 tbi been doing it since I've owned it I agree with the piston slap just drive it until it goes that what I'm doing.... I'm saving up for a 5.3 LS swap in mine just gotta have a reason to do it lol

 

[gmcyukondriver]

A little late, but I did want to let everyone know what it was.

A bolt on my tensioner bracket had backed out (keep in mind, my tensioner is not where yours is), so the bracket was slapping the A/C Compressor bracket on startup. Eventually, it moved back and forth enough that the belt slipped off and wrapped around the fan. No damage, but that helped me figure out what was going on. It's all fixed and no more noises on startup.

 

[skylark]

http://youtu.be/Rx6WB5YJia8

How oh how did I miss "midget under my hood? ".
How about a trunk monkey instead?

 

[sewlow]

Oh no! NOT 'Trunk Monkeys'!