i have a 2007 Cobalt ss/sc and every few starts there is a loud knock for the first 3 secodns or so the engine is running. anybody have ideas on what this might be?

 

pistons? Lol...****. I have an 07 stock......it is only on start up. not even every start. it is pretty loud though. think it could be a motor?

 

Nope, not pistons. It is the Timing Chain Tensioner. The car needs to build oil pressure on cold start ups. It has to get oil to the top of the motor on the DOHC motor, unlike a pushrod motor. The pressure is built mechanically at first, and then hydraulically once pressure is built up. You are hearing the mechanical portion of building pressure immediately after start up. I have had this problem since I bought my car, have had the tensioner replaced at 4000 miles (I have 21,000 now). GM told me that it has no adverse affect on the motor and will only be replaced under warranty by owner request. It still makes this noise to this day, but only on first start up afetr sitting 8 hours or more. It lasts about 5 seconds and then goes away. If I were to shut off the car and immediately re-start it, there would be no noise.

These ECOtecs are loud clackity motors, too many moving parts for my liking!

 

is this the loud sound, like someone is knocking on your trunk? if so that's normal. exhaust gases

 

That is my question too, does it sound like someone knocking on the floor or trunk of the car? If so, it may just be the fuel pump doing a pressure check.

 

I had this similar thing wrong with mine but it goes a way after it warms up if this is what your does then it this little senson by your fuse box makes a loud ticking or knocking sound my dealer said that it has to do with the air and he showed me on one cobatl that was never started i herd it and sounded exactly the same but if it dont go away its not this or this is a bad sensor now you should reconize a piston or rod knock casue its constent

 

Maybe piston slap??

 

Well it could definatley sound like somebody is smacking on the outside of the car once or twic.e....what does that mean?

 

Where is the sound coming from? from the front or rear of the car? If it is coming from the rear then this is probably just the fuel pump.

 

it sound slike the frotn of the car....i was thinking maybe a cracked mount or...

 

Document ID# 1890375
2007 Chevrolet Cobalt


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Subject: Noise from Rear Of Vehicle - keywords canister cold CVS click evap knock L61 LE5 noise rear solenoid tick vent #PIC4317B - (01/23/2007)



Models: 2006-2007 Saturn ION

2006-2007 Chevrolet Cobalt

2007 Pontiac G5

2005-2007 Pontiac Pursuit

with Engine RPO L61 or LE5




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This PI is being superseded to update technical information. Please discard PIC4317A.


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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A noise may be heard from the rear of vehicle; typically 3-5 knocks during initial cold start. The noise may sound like someone outside of the vehicle is tapping on the back window or on the rear exterior body panels.

Recommendation/Instructions:
This noise is from the vehicle's EVAP canister vent solenoid going through the diagnostic cleaning cycle, which is part of the software calibration set-up. Replacing the EVAP canister may not resolve the issue when the vehicle is re-exposed to a cold start. No parts should be replaced. This should be considered a normal condition for 2007 and previous model years.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

That's the ticking noise from the rear, a fuel pump will sound more like a steady hum for about 3 seconds. If you are sure the noise is from the engine, it is because of the oil not reaching the top of the engine fast enough. You do have mobile one in your car right. An oil that is too thick usually cause this to be a lot worse then normal operation. Most of Gm's trucks have this as a normal condition also a bit of a piston slap while the rings get warmed up and expand due to such tight tollerences built into these engines.

 

I've heard this sound a few times as well but mine is definitely coming from the front of the car. I've also heard it before on my '98 Sunfire GT and my wife's '96 Grand Am, so I don't really know what it could be...

 

i have the same problem. the knock is coming from the frount and it is going to the dealer on tuesday. Also something is wrong with the cat and the paint is fucked up and chiped on the back so they got alot of work to do on tuesday. and by the way the dealer said that the knock is not normal!!!!!!!!!!!!

 

I have the same issue, its a oiling issue. Different oils will stop that. I uise sythetic penzoil, seems to be quiet. I had the startup issue as well, after about 10K it was gone. barely does it. Change your oil, use a sythetic, see how it works out. In my opinioon, 5w30 on these motors is to thin. They run hot. so its very thin oil.

 

^ mine has around 15,500 miles and it started ticking on startup bout a month ago. i think it's something in the tranny because when i take off in first gear for the first, time you can hear it tick then it goes away. going to the dealer friday..

 

Sure this thread is old, but it might be that your oil filter has never been replaced: https://www.cobaltss.net/forums/general-cobalt-68/dont-change-your-own-oil-check-out-122792/

happened to me, it can happen to you. Good luck!

 

have you ever noticed that at an idle, your engine (2.0L SC) sounds like a threshing machine?
That has aggravated me since Day One. Sitting there at an idle, it sounds like a 350 chevy with 276,000 miles on it. Hit the gas, noise goes away until drops back to idle... It doesn't do it all the time, only when it's 185+F and you've just come down from speed, or pulling a hill... Will going to a thicker Mobil 1 help?

 

same with me only happened once since i owned the car I don’t know when i put it on first gear it was completely gone. What did the mechanic told you tho?