3400 SFI Engine Noise

You are probably hearing what is referred to as " piston slap". Fairly normal on these engines, but they can be fixed. We replace pistons on them all the time. I just did one yesterday.....it was way over warranty, but we "good-willed" the repair as it's an obvious defect in these engines. Contrary to what most people believe, GM is fairly good about standing behind their product if it's a "known" problem. When you dis-assemble these engines, there is actual physical damage to the pistons....which is why GM fixes these engines, but doesn't bother with the newer small block v-8 engines.

Ian

Oh, well then I guess my next question is. When this car hits 200k miles, do you think it will still run? Its my moms car, and she doesnt drive it hard, I stomp on it now and then, but it gets its oil changed every 3k miles, and we use a synthetic blend 10w-30. Hopefully GM will cover the problem if something like this ever happens because of the defect of the engine. I swear my 4.3L in my S-10 does it every now and then, I can really hear it when its warm. Its not a knocking either.

Howcome it doesn't bother with the 5.3's. Mine sounds like crap from new. Brought it back twice they say its normal.

lol, I know what you mean. My mechanic has a 2001 Silverado with a 5.3, and his does it too. I heard that GM bought back an undisclosed amount of these vehicles because of this problem, not sure if its true or not. But eventually the engine will take a s*it because of this problem, atleast thats my opinion. I love the 5.7 Liter and the 4.3 Liter. Always owned one or the other or both and they both have the power i need and they are very dependable.

Probably because there is no real physical damage being done to the engine. I started a 1999 new style truck up the other day and it sounded "horrible". But the noise was gone within a minute or two of running. 3.1/3.4 engines that are really bad will be noisy at all tempertures. And there is real and observable physical damage to the pistons. Since I've never seen a new style small block engine apart for this type of noise, I cannot comment on what the pistons look like with this noise. When I finally see one apart....I'll probably comment on it.

Ian

Ian is GM fixing the engine because of customer noise complaints or actual engine failure? My 98 Montana w/3.4l engine has 106K miles and rebuilt at 30K miles by GM because of cold start tick. The TSB talked about the noise source being caused by the connecting rod to wrist pin fit. The fix was new fitted piston assemblies. The noise never completely went away but was considerably less after the rebuild. Now at 106K it can be fairly loud for the first couple minutes after a cold start but goes away. Of interest when it's started in 50F or less the noise is noticable reduced. I just stopped worrying about it and change the oil every 4000. Still using 5W-30 and comsumption is nil between changes.

I've never seen an actual "failure" because of the piston problem. In other words, I've never seen an engine blow up, stop running...etc ...due to this problem. They just get very noisy.

Yeah, at one time that was either the theory, or maybe it was the problem, but I've always seen the piston skirts scuffed. This problem has been around for years of the 60 degree v-6's. When the Pontiac transport came out, we were replacing the front three pistons in those engines like crazy. Even today....it's almost always only one bank of pistons that displays the problem.

You will probably run that engine till it dies or you sell it with no failure.

Ian

My Father-in-law has a 3.1 in a Cutlass with 249,000 miles, still runs, though it does sound kinda rough. Like the pistons are swapping holes or something.

Hey Ian, I heard that in the 80's, GM coated some of their pistons with tin, is this true? In high school I used to drive an 1989 Buick Regal with a 2.8 Liter MPI V6. It had the loudest knock you have ever heard, I ended up having to rebuild that engine. My mechanic told me GM did that with some engines. Just curious if GM actually did that, and if so, why would they do something like that?