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GMC Forum: Piston Slap
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  #1  
Old 06-22-2011, 10:57 PM
rogerj rogerj is offline
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Default Piston Slap

Piston slap in #2 Cyclinder 4.8 V-8 Vortex 2001 GMC Sierra work truck. 11100 miles, Book says OK, BS... winter rattles-summer smooth as a b---
a---, Original owner.
Tell it like it is, I can take it.
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  #2  
Old 06-29-2011, 09:03 PM
Bill325 Bill325 is offline
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Default Piston Slap

I'm a new member. Hello to all of you ! I just bought a 2000 GMC Sierra pickup, longbed , standard cab, with the 5.3 liter engine. I bought it from a new car dealer, where it had been traded in. The truck has been kept in beautiful, nearly showroom condition, and has 119,000 miles on it. However, it also has a piston slap when it's cold started in the morning, but only lasts 30 to 40 seconds in this summer weather. It sounds like a diesel engine rap. After that, the engine is quiet. Oil pressure builds to 45 lb. within 2 seconds, on the gauge. I was surprised to hear the noise the first morning after I drove the truck home from the dealer. Then I realized that both times I test drove the truck, the dealer knew I was coming, so he warmed the truck up both times prior to my arrival. (Lesson learned- always take them by surprise. ) Even so, I'm happy with the truck . That piston slap issue has been much discussed , and the bottom line seems to be that GM says it's mostly a nuisance noise, and that any piston slap noise that goes away within 2 minutes of a cold start is " acceptable". But, many owners say it's an obvious defect and should have been the subject of a recall. I plan to keep my truck , and hope the piston slap doesn't cause serious wear issues or oil burning. I'm switching the engine to Mobil 1 10W-40 full synthetic, which Mobil says was designed for engines with over 75,000 miles. And I'm using an oil filter with an anti-drainback valve to help build faster oil pressure. Possibly, the lubricating properties of the synthetic oil will help keep the piston slap from getting worse. I also have that pesky bad gas gauge problem, but that's another thread.

Last edited by Bill325; 06-30-2011 at 12:06 PM.
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  #3  
Old 06-30-2011, 01:45 PM
Rowdy_GMC Rowdy_GMC is offline
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i also have the same problem. my 07 gmc sierra has a piston clap. it prevents me from doing auto start. and also is very annoying when i gas it, it sounds faster and louder. i use royal purple synthetic oil 10w-40 to see if it would fix it but its hasn't. please someone help. its throwing out a code, TPS sensor.
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Old 06-30-2011, 03:20 PM
Bill325 Bill325 is offline
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Rowdy- Provide us with a little more information . How many miles on your truck ? How long have you had the piston noise, and does it get quieter after the engine warms up ? It might be a rod bearing . What is auto start, and why would a piston noise prevent it from working ? The TPS is the Throttle Position Sensor, and should not be a factor in your engine noise. If the TPS code indicates a defective sensor, you should be able to measure the changing voltage output as the throttle moves, and determine whether it's bad. The TPS shouldn't cost too much, and if in doubt, buy a new one. I don't know what other faulty components might show up as a TPS code, so consult a shop manual. I just bought a set of factory shop manuals for my 2000 Sierra from Helm publishing. They were $135 , and consist of 4 volumes totaling 6,000 pages ! ( with very poor indexes). I'll do some reading in my shop manual, and see what else would trigger a TPS fault code. Remember also that dirty connectors in the wiring often cause problems, so buy some electronics spray cleaner and start separating engine compartment connectors and cleaning them.

Last edited by Bill325; 06-30-2011 at 03:25 PM.
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  #5  
Old 06-30-2011, 05:54 PM
rogerj rogerj is offline
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This has really stumped me, if only one cyclinder has this noise, what's happening to the other seven?
I have lost gas millage sence I have had the 100,000 mile tune up and one problem has developed. the change oil light came on and stayed on,
I was close to a GMC dealer, problem solved, mechanic assured it was only a little carbon from cleaning of injecting tube. Yea sure! Light came back on when brought back. When we lifted the hood and removed the oil cap it sounded like there was preasure built up inside. Then the change oil light went out. I haven't had a problem sence accept the poston slap. The change oil light works fine and I have reset it more then once. (5 seconds 3 pumps). Looks like it will be after summer till I get another chance to hear it again,
Lucky Me.

ROGERJ
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  #6  
Old 06-30-2011, 06:07 PM
rogerj rogerj is offline
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This has really stumped me, if only one cyclinder has this noise, what's happening to the other seven?
I have lost gas millage sence I have had the 100,000 mile tune up and one problem has developed. the change oil light came on and stayed on,
I was close to a GMC dealer, problem solved, mechanic assured it was only a little carbon from cleaning of injecting tube. Yea sure! Light came back on when brought back. When we lifted the hood and removed the oil cap it sounded like there was preasure built up inside. Then the change oil light went out. I haven't had a problem sence accept the poston slap. The change oil light works fine and I have reset it more then once. (5 seconds 3 pumps). Looks like it will be after summer till I get another chance to hear it again,
Lucky Me.

ROGERJ
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  #7  
Old 06-30-2011, 09:34 PM
Bill325 Bill325 is offline
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I don't know about the change oil light issue. However, the piston slap problem often involves only one or two pistons. There's a variety of information on the web about this issue, including mentions of special coatings on some pistons but not others, and carbon buildup on the pistons above the ring lands. However, the bulk of the information indicates that GM stopped individually fitting pistons to cylinders to ensure proper clearance. Instead, they apparently decided that their quality control was good enough that every piston would fit every cylinder without confiirming the clearance.
Hence, if you happened to combine a slightly undersized piston with a slightly oversized bore, you have too much clearance, and get piston slap. The problem was apparently made worse by a switch to short skirt pistons, which encourage piston rock. According to the factory manual, a similar noise can be made by excessive wrist pin clearance too. Usually, the noisy piston is identified by disconnecting the spark plug wire to that cylinder, which lowers the combustion chamber pressure and temporarily stops the piston slap. In my humble opinion, if the noise disappears after the engine is hot, then you can live with the issue. If the noise never goes away, then engine damage is probably occuring . Apparently, the symptoms will include excessive oil consumption in that cylinder, unusual carbon buildup in that cylinder, and unusual piston and cylinder wear. I also suspect that the wrist pin and connecting rod bearing may suffer an early demise from the shock loading.
However, GM apparently extended the warranty on some of these engines with piston slap to 100,000 miles, as a show of confidence that the problem can be lived with.
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  #8  
Old 07-01-2011, 01:26 AM
rogerj rogerj is offline
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Sorry to say, I won't be buying another GMC for awhile. GMC don't make them like the use to. My old 77 made 240,000 no leaks, noise, no problems!
Thanks for the info.
ROGERJ
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  #9  
Old 07-01-2011, 10:30 AM
Bill325 Bill325 is offline
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While the piston to cylinder clearance was reportedly an issue, it seems odd to me. Many of us have had engines that went 200,000 miles or more, and never developed piston slap. The cylinders in those high mileage engines had plenty of wear , and the clearances get large indeed. But still, no piston slap. It seems to me that the clearance issue is secondary to a piston design defect in the engines with piston slap. I've read about the shorter piston skirt design, reportedly done to reduce piston drag and improve fuel economy. Piston design is a complex thing, and new designs are constantly coming out, but in my 63 years, I've never before owned a vehicle with obvious piston slap noise. I think GM dropped the ball badly on this issue. ( Is there, by any chance, a tiny little script on those pistons that says " Made in China" ?)
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  #10  
Old 07-01-2011, 08:24 PM
happy 2011 happy 2011 is offline
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i know some of you are going to jump on me for this but

well i think you all are over reacting a little bit here. 9 9 percent of pistons made today are coated. Yes some pistons will make a noise when cold (even new ones) this is done becaues when the piston heats up it Expandes to to seal the cylinder with the rings. This makes longer engine life belive it or not.

Plus you think GM piston noise is bad you should hear fords -sounds like a diseal - subaru - sounds like a it's going to blow any min. And yes toyota as well can't even get away with no piston noise.

Nothing happens becaues of the noise and it does not take away from engine life at all. It's just you were taught that engine noise was bad Not always true.
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