Midlife crisis

Hypochondriac here again. Chevrolet dealer mechanics say I'm OCD. Anyhow, like a lot of folks here, 2002 camaro with LS1 117000+ miles, SLP Blackwing, HPTuner, make a loud knock on start up on cold mornings. Start RPM around 1000 then when idles back knocking starts. Really loud when shift into gear. Ater warm up quiets considerably. Learned everything I can about the "piston slap" but now I'm concerned about the loss of fuel mileage. 50-60 mpg fall of per tank since all started. Thought it was because I let it warm up a lot, but this week tried to just ease out slow until warm and still seem to loose a lot. Someone mention a possible exhaust leak on the last thread I posted. Throwing off the o2 sensors... Do I just ask mechanics if they can do a smoke test or is that something I can do at home? Also can the local parts stores ( oriellys, autozone...) scanners do the real time scanning to check sensor readings even with no warning light? Any tips or suggestions would be appreciated. Read enough posts to anticipate what everyone will say but interested to hear. Thanks
Alan

garygnu

you can buy a scanner from HB and check you O2.or just buy new O2 sensors and install them.consider cleaning your MAF.if you have a friend with a ls1 f-body ,borrow his MAF and install it in you car for a week or 2.also check your starter to make sure it is tight .

andrewss

iTrader: (1)

Funny, I heard my buddies 02 SS start up last night after being in the cold, the piston slap was pretty loud then went away fairly quick. I would say if it goes away when warmed up not to worry.

92v

iTrader: (1)

My 2000 WS6 has a bit of knocking sort of noise when it is cold, that goes away when warm. I have convinced myself that it is because the block and heads are aluminum and almost all of the moving parts in them are steel and they expand at different rates. This may be complete self delusion, but I don't care because I can't afford for it to be anything else. I just take it easy when its cold and don't worry about it when warm. I have put 2000 miles on it since I bought it 6 weeks ago, with zero problems.

Gates72ss

Piston Slap....Almost every Modern chevy i have owned did it too some degree..Once you get used to it it wont bother as much until you go through a drive up window..

2000PewterT/A

Just sounds like general piston slap to me, nothing I would get worried about. Now this is most likely is not your problem but one thing people tend to get all worked up about fuel mileage is when they switch to winter fuel their mileage does decrease some. Now it shouldn't be a crazy difference but it can be noticeable if you keep track. Nothing you can do about it. Now you may not have winter fuel where you are but that is one thing to keep in mind before trying to fix a fuel economy problem. I would still scan it and see what your o2 readings are and see if they are lazy.

TransAmBlue

My 01 WS6 knocks badly cold and warm still knocks at a idle. These engines can be noisy, some worse than others.

Your fuel mileage could be down because of carbon build up, carbon build up can cause alot of knocking at cold start too.

Either buy a carbon cleaning product or ask the dealer if they offer a carbon cleaning service.

I'll give you an example my 99TA knocked TERRIBLE cold and sounded like a diesel warmed up. Drove it like this for years without any trouble until the trans needed work. The dealer decarboned the engine when they did the trans, car was quiet as a mouse after that! NO MORE piston slap! So it was actuall carbon noise all along.

What happens in a Aluminum engine is as the engine runs and gets hot it expands, carbon builds up on the pistons and cylinder heads while the engine is expanded. NOW you turn the engine off and it cools and contracts, SO when you restart cold the cabon on the pistons is hitting the carbon on the cylinder heads.<NOT PISTON SLAP, but sounds like it.

REAL PISTON SLAP NEVER GOES AWAY, you will always hear it a little even warmed up.

Carbon noise DOES GO AWAY after the engine is warm and will effect fuel mileage greatly.

TransAmBlue

Thats some funny stuff, 1st time I took my WS6 through McDs I about **** when I realized all that knocking was MY CAR!

Gates72ss

I swear those drive up windows have sound amplifiers built into the walls...

98WS6Hville

iTrader: (7)

^ YES!! Some days it's awful and it's embarrassing using the drive through window because of that noise. Other times the noise is very minimal. Glad to know I'm not the only one. I'm so paranoid about my car.. LOL

TransAmBlue

I think most of the noise you hear in a LS1 is the lifters. They can make quite a knocking noise and honestly EVERYONE tries to pass any kind of knocking in a LS1 as PISTON SLAP.

I was at the dealer once with my 99TA for engine noise, the lifters were rapping terrible. THEY TRIED to tell me it was piston slap!
They knew dam well it was lifters. See if its piston slap GM says it nothing to worry about, lifters on the other hand need replacing.

Piston slap doesn't sound ANYTHING like a lifter!

Midlife crisis

@ garygnu- I will be off the next few days and already have a few shops that will read the sensors for me. Seems the parts stores dont have the scanners much better than already have. But looking forward to some of the diagnostics.
@92V-I hear ya. same boat here. I dont want to break it. and turn a low dollar fix into a major rebuild though.
@transamblue-I hope this week to be confident in what the problem is. Sorta takes the fun out of owning it when you have to worry about it all the time. Thanks for the advice. I get so many different Points of view. Im sure It will sort out in the mix.
Thanks to all who respond. Ill let everyone know when i learn for the collective knowledge.
Thanks all

blknSS

Lmao....if they give me a funny look at the drive-thru I usually kick it sideways leaving.

Gates72ss

Agreed!!! You can def tell the difference between the two if you have a keen ear and have been around motors enough..
Most of the time with the newer gen chevy motors it is actually just piston slap when the car is cold like he was describing..The ls motors are noisy anyhow with the aluminum block / heads , aluminum is a much better sound conductor ..
It is something to def get checked out, wouldn't want anyone thinking it is something simple and blow up their ride..