yet another question about cold engine starting...

taki1 · October 20, 2002

I know there are a million topics on the subject of cold engine knock/piston slap, but heres one more...

Ive got a 2002 5.3 z-71 that i bought in march...never made a noise on startup until the weather outside got to 30-40 degree range...then it makes a noise for 10-15 seconds when it is started - a loud clicking noise, which speeds up if the throttle is bliped...I change the oil at 3000, and only use pf-59 filters (with the anti drainback valve)...

However, when I park in the garage on those 30-40 degree nights, and I go to start it up in the morning, there is no noise....

Can anybody tell me what this noise is? fuel injectors, noisy lifters, piston slap? something else?

Ive read so much crap on the subject that I dont know what to believe anymore...

bcfitzsimons · October 20, 2002

Probably a mix of lifters and carbon buildup on pistons. GM uses fast-bleed-down lifters for emissions purposes, so more of them are going to need filling after a night of sitting.

As for carbon buildup, there's an easy way to figure out if your cylinders/pistons are dirty. Get some top end cleaner from a GM dealer (aerosol's easier to use than the liquid) and spray it through the throttle body of your engine at your next oil change. Let it sit for a few hours, or overnight. The next morning, drive the engine hard for 30 minutes, then change your oil (the stuff dissolves carbon, and it all drips into the crankcase). If your clatter improves, then you have your answer. It certainly worked for my 8.1 L! HTH-Fitz

taki1 · October 21, 2002

Thanks for the insight...

I wouldn't have thought that an engine with 7000 miles on it could have so much carbon buildup that it would cause a noise to be heard...but stranger things have happened...

TxDoc · October 21, 2002

http://www.gm-trucks.com/cgi-bin/ib3/ikonb...029;hl=gm+reply

From April:

Basically:

1-GM is aware of it.

2-It is not causing damage.

3-no fix is coming in the soon to be released TSB.

From Truck Trend:

"There've been a lot of complaints about cold-start knock in the Vortec engine family and most General Motor's customers are getting incomplete answers at dealerships. We've spoken with Matt Kester, assistant manager with GM Powertrain Product Comunications, about this situation. He said General Motor's engineers ARE AWARE of the problem and are currently in a RESEARCH STAGE. The cold-start knock involves the 4.8L, 5.3L and 6.0L V-8s in all applicable GM cars and trucks from '99 to '02. They believe the CAUSE IS carbon buildup on the circumference of the piston ABOVE the top piston ring. This interference is affecting the dynamics of PISTON TRAVEL and therefore causing a knock. It seems the problem begins after the first 12,000 to 15,000 miles and the knock will last between five and 30 seconds in temperatures below 50 degrees after a cold startup. The noise also seems more pronounced AFTER long trips and at lower temperatures. The use of a top engine cleaner will give only TEMPORARY results, IF ANY, and a replacement engine without modifications would most likely develop similar symptoms. We were also told that a Technical Service Bulletin is in the process of publication, which should provide and explanation of the condition, BUT NOT A FIX, and that carbon deposits and associated knock ARE NOT CAUSING ANY STRUCTURAL DAMAGE TO THE ENGINE. So,for now, don't let it bother you. We'll give you further details when the TSB becomes available."