Sputter/ticking sound on cold start

BigChungus

BigChungus

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Truck is making this crazy sound on cold start. Cant hear it in the truck and it’s coming from the motor and not the exhaust. But it could be from the manifold. Goes away after it idles down. Anyone know what this is. Taking it to dealer tomorrow to have a look but want to come armed with some ideas of what it could be.
 

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I had an issue several months back where mine would start rough on a cold start, and eventually turn itself off, with the smell of backfire in the air. I got a CEL and all kinds of other warnings lights. I took it to my dealership and they re-flashed it and it seemed to be fine, then a couple months later the same thing. This time I called OnStar while I was in the truck and they emailed me a diagnostic. The coil pack on cylinder 4 was misfiring and causing the issue. I got it towed and the coil pack replaced within a couple days (luckily my dealership is the least busy in the lower mainland). If it’s doing it when you start it to take it to the dealership, call OnStar and tell them your issues and ask them to send a diagnostics to yourself and your dealership. I think if I didn’t have mine the dealership would’ve just re-flashed it and wait till the problem happened again. Hope this helps in some way. We may have completely different issues. Good luck 🍀
 
BigChungus said:
Truck is making this crazy sound on cold start. Cant hear it in the truck and it’s coming from the motor and not the exhaust. But it could be from the manifold. Goes away after it idles down. Anyone know what this is. Taking it to dealer tomorrow to have a look but want to come armed with some ideas of what it could be.
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Mine makes the exact same noise...I have not taken it to the dealer yet and am very interested in what you find out from the dealer. It only makes the noise on "first start/cold start"...when the engine is warmed up and restarted with a good cool down, it will not make the noise. It sounds to me like an exhaust leak which seals when the manifolds get warmed up and expand??? Please let us know the fix
 
I hate dealing with dealerships. I set an appointment to have it looked at and they told me it’ll take a few days to get to it even after I told them I would be waiting on it for the diagnostic when I set the appointment. So I’ll be dropping it off tomorrow and leaving it with them. Service guy said it sounds like the idler pulley bearing or another bearing in the motor making noise but won’t know till it’s in the shop. I’ll update when I get it back.
 
BigChungus said:
I hate dealing with dealerships. I set an appointment to have it looked at and they told me it’ll take a few days to get to it even after I told them I would be waiting on it for the diagnostic when I set the appointment. So I’ll be dropping it off tomorrow and leaving it with them. Service guy said it sounds like the idler pulley bearing or another bearing in the motor making noise but won’t know till it’s in the shop. I’ll update when I get it back.
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that sucks...good luck with the rig.
 
Update: dealer looked and said the noise is completely normal. It is coming from 2 exhaust valves located between the manifold and catalytic converters. Said they are electronic and the noise is gas passing around the valve while it opens. Apparently a lot of the 6.2s make the noise. At least it’s documented just in case something happens.
 
BigChungus said:
Truck is making this crazy sound on cold start. Cant hear it in the truck and it’s coming from the motor and not the exhaust. But it could be from the manifold. Goes away after it idles down. Anyone know what this is. Taking it to dealer tomorrow to have a look but want to come armed with some ideas of what it could be.
Click to expand...
Could be belt, fan, air leak....video too short to really tell.
 
BigChungus said:
Update: dealer looked and said the noise is completely normal. It is coming from 2 exhaust valves located between the manifold and catalytic converters. Said they are electronic and the noise is gas passing around the valve while it opens. Apparently a lot of the 6.2s make the noise. At least it’s documented just in case something happens.
Click to expand...
Not sure I buy that diagnosis.
 
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Bigchungus,

Was that the adaptive flapper valve they were referring to? I looked for a "valve" between the manifold and the catalytic and could not find a part, diagram, reference to one...the only reference I found was the adaptive flapper valve...lots of reference to it online. Im curious about that diagnosis as well...if that were normal, everyone would have that noise.
 
Troll said:
Bigchungus,

Was that the adaptive flapper valve they were referring to? I looked for a "valve" between the manifold and the catalytic and could not find a part, diagram, reference to one...the only reference I found was the adaptive flapper valve...lots of reference to it online. Im curious about that diagnosis as well...if that were normal, everyone would have that noise.
Click to expand...
Ya I’m not buying it either. The truck is still running great and the sound goes totally away after 15/20 seconds after cold start and doesn’t come back when the truck is warmed up. When I get some time I’m going to take it to the other Chevy dealer in our area and see what they can find.
 
BigChungus said:
Update: dealer looked and said the noise is completely normal. It is coming from 2 exhaust valves located between the manifold and catalytic converters. Said they are electronic and the noise is gas passing around the valve while it opens. Apparently a lot of the 6.2s make the noise. At least it’s documented just in case something happens.
Click to expand...

BigChungus said:
Sounds like all of the above but the tech who looked it over checked all of this and nothing was found.
Click to expand...
Yeah something is weird about that...Maybe next time you're there, ask them to start a few up for you so you can listen for yourself. Unless those are there for that exact same noise reason, that should set your mind at ease a little more knowing.
 
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