Engine Knock

ksu1018 · October 5, 2006

Knock sensors? Where are those located? Are they easy to replace? What is the cost of them? I have a 2001 GMC Sierra SLE it mostly does the knocking at cold start ups.

AirForceAngler · October 7, 2006

2000 Silverado with 5.3, it has been doing it since 45,000 miles and it now has over 104,000 and no problems. Still pulls like a mule and keeps going.

ngrcff06 · October 8, 2006

2004 Yukon XL 2500 8.1L Knock on almost every start (cold or warm). 40k miles now, been doing it since <1000. GM says its "normal."

Green_Monster · October 24, 2006

Well it's been in cold weather and I have 26,000 miles now. Still no knock (piston slap). Not even at start up.

Pureiron · November 10, 2006

I have noticed in some of the threads, that the folks that switched over to synthetic also seemed to get rid of the knock. I have a tick, and it only lasts 10 seconds. Still using dino though. I am gonna switch to syn next change and I will come back and repost if i see the same difference. I also saw a post on here that stated after he got the wait 4 me tune, his knock was gone. Dunno folks, ill b back

duffus · November 12, 2006

99 Z71, 121k miles---slight knock/tick the first 10s of startup-- more pronounced in cold weather. I have two theories:

(1) the lifters are making the noise, when the oil is pumped to the top of the engine, it stops

(2) piston slap -- only it hasn't gotten worse. Piston slap is when the bore and piston diameter are just enough apart that it, in effect, "rotates" some in the cylinder until the piston heats up and expands, closing this gap that is probably 0.0005".

The noise has never gotten worse, and this mild-mileage truck still flies.

c4cruiser · November 12, 2006

Knock sensors? Where are those located? Are they easy to replace? What is the cost of them? I have a 2001 GMC Sierra SLE it mostly does the knocking at cold start ups.

<{POST_SNAPBACK}>

Knock sensors have nothing at all to do with what is typically called "piston slap" and that is basically what is being discussed here.

The knock sensors can be located at the ends of the exhaust manifolds or right at the start of the exhaust pipes before the catalytic converters. Their purpose is to detect a knocking sound brought about by detonation in the combustion chamber. Detonation is typically the fuel and air mixture exploding from hot spots in the combustion chamber and not be ignition from the spark plug.

When the sesnors "hear" a noise, a signal is sent to the ECM which then retards timing or changes the air/fuel mixture to help stop the detonation. Detonation is a bad thing the combustion chamber; pistons can melt and/or connecting rods can be bent or broken under the force of the detonation.

Z71SIERRA · November 15, 2006

My 02 5.3 with 60,000 miles on it does not knock but I did have a start up knock for one oil change cycle back when it had @ 34,000 miles on it. I figured I had just been cursed with "the knock" but when I changed the oil the next time I found that the delco oil filter had a defective drain back valve. The rubber valve was folded on one side and you could see it through the oil passages in the filter. I now use a Mobil One filter and I haven't had a noise since. The Mobil one filter (and oil) are both too expensive but I've never replaced an engine part because I used too good of oil and filter and changed them too often.

cokesda1 · November 27, 2006

2000 Silverado with 5.3, it has just started the last year at around 100k. Seems to have gotten worse as I now drive 90% city driving VS 90% Highway driving up to last year. Knocks for about 30 seconds and is more pronounced on cold morings. Little to no knock on warm mornings. Have 111k now.

Glen Koenig · November 27, 2006

2000 Silverado with 5.3, it has just started the last year at around 100k. Seems to have gotten worse as I now drive 90% city driving VS 90% Highway driving up to last year. Knocks for about 30 seconds and is more pronounced on cold morings. Little to no knock on warm mornings. Have 111k now.

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2002 Silverado 6.0l with just over 50K miles.

I get about 10 seconds of piston slap every morning until the slugs gets a little heat and expand, then it's all quiet. Mine is due to the known issue with the pistons as has been stated here.

I'm not surprised that there is a law suite over this. Not that there is any reason for GM to do anything about this non-issue. But hey, if a lawyer can make a few hundred million in order to get each of us a $5 discount on our next oil change at the dealer and punish the gready SOBs, then by god they'll do it!

04silverado1500 · November 29, 2006

is the knock you guys have loud enough to hear inside the cab also cant you just fix it buy running 89 octane through it or somthing. at idle i have a little tick or somthing but it sounds really quiet ill have to run 89 and see if it make the noise. because you cant hear it outside the truck

drumset5994 · November 29, 2006

Mine was during the cold, after 2 days of non-use. I started it up, and it sounded like it was going to seize...as i reached for the key to turn it off...it disappeared.

It scared the s**t out of me.

redvett · December 12, 2006

2000 Ext 199000mi NO still in my fleet

2001 Ext 151000mi NO still in my fleet

2002 Ext 101000mi NO still in my fleet

2004 Ext 40000mi NO my personal truck.

All are 5.3 4x4 and we use Mobil 1

ARAMIK · December 13, 2006

Not sure if I have it or not! I have a tick kind of noise at idle, but you cant really hear it from in the cab! When I rev the engine it either goes away or I just cant hear it because of the engine revving. Hopefully I dont get the knock or whatever you guys have!

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My Focus SVT does that and it's the fuel injectors...that might be what you're hearing...

06 GMC Sierra 5.3 11,000 miles - NO KNOCK.