Sounds like someone has gutted the catalytic convertor on this one or it has a mild exhaust leak. Run it by your local muffler shop and have them check the exhaust system. If your not hearing anything under the hood or inside the front fender wells then this is all in the exhaust system. Note: It is important to get any exhaust leak repaired promptly. In certain cases deadly carbon monoxide can get into the passenger compartment.
Engine knock from exhaust when cold
- Thread starter Therealsmitty
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SnowDrifter
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Sounds like either a rotted out or aftermarket exhaust to me. It will sound different hot vs. Cold. Engine will use a different air/fuel ratio between hot and cold, both for performance at low engine temp and to warm up the cats. Different timing too. You can absolutely hear the difference
Therealsmitty
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Hmmm, I suppose it's possible it could be an exhaust issue; it did pass NV air inspection in Jan of this year, so I don't think it's a gutted cat. I took it in for air inspection here in CO but apparently the traction control won't turn off even though the dash says it's off when you toggle it. For that reason they've not been able to test it yet. I'm pretty sure I know the culprit in that problem, just need to fix it so they can try again.
I have to say, it's a very pronounced knock sound when you hear it in person. When you say it might be an exhaust leak I think you're getting the impression from the recording that it's more of a resonance or hollow sound, but it's not.
All that said, unless it indeed has something to do with the exhaust warming up, it does seem odd that it goes away once hot. I'll be putting in 0w-30 full synthetic tomorrow and will update.
I have to say, it's a very pronounced knock sound when you hear it in person. When you say it might be an exhaust leak I think you're getting the impression from the recording that it's more of a resonance or hollow sound, but it's not.
All that said, unless it indeed has something to do with the exhaust warming up, it does seem odd that it goes away once hot. I'll be putting in 0w-30 full synthetic tomorrow and will update.
@Therealsmitty, this won't help now if you are in the process of getting license plates in Colorado. But for the future if you have to go through emissions testing in Colorado (usually every 2 years with older vehicles), you don't necessarily have to have it tested at an Aircare site and you can skip the traction control, gas cap, etc. issues.
Within certain timing guidelines you can pass a couple of tests at the mobile RapidScreen sites that move around the area. This site shows the upcoming locations:
http://aircarecolorado.com/index.php/rapidscreen/truck-locations/
Last time my Hoe needed the inspection was after my son had used it for a couple of months. He passed by the RapidScreen mobile site a few times over a couple of months, and when the license renewal came in the mail it said the truck had passed and no additional emissions test was needed. Nice surprise! Still had to pay the $25 with the registration but it was a lot more convenient than having to take it somewhere.
Some people intentionally plan their route to go by mobile sites so they won't have to visit the Aircare garages.
Within certain timing guidelines you can pass a couple of tests at the mobile RapidScreen sites that move around the area. This site shows the upcoming locations:
http://aircarecolorado.com/index.php/rapidscreen/truck-locations/
Last time my Hoe needed the inspection was after my son had used it for a couple of months. He passed by the RapidScreen mobile site a few times over a couple of months, and when the license renewal came in the mail it said the truck had passed and no additional emissions test was needed. Nice surprise! Still had to pay the $25 with the registration but it was a lot more convenient than having to take it somewhere.
Some people intentionally plan their route to go by mobile sites so they won't have to visit the Aircare garages.
Sounds ok to me. I had a Trailblazer with an early 4.2. That thing had so much piston slap when it was cold, it sounded like a diesel. Dealer said it was normal, and it never gave me problems in the 12 years I owned it. Loved that little SUV.
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Therealsmitty
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Fless:
That was my thought exactly, but at the DMV they told me it was to renew only, and that it likely wouldn't work with the temp tags they gave me. I'll have to read all the fine print or give them a call to double check this. We have a Rapid Screen van that's in Castle Rock quite often fortunately. Thanks for reminding me to look into that!
That was my thought exactly, but at the DMV they told me it was to renew only, and that it likely wouldn't work with the temp tags they gave me. I'll have to read all the fine print or give them a call to double check this. We have a Rapid Screen van that's in Castle Rock quite often fortunately. Thanks for reminding me to look into that!
Therealsmitty
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Boatguy: I actually just sold a trailblazer with 170+k on it that indeed sounded like a diesel for the first few minutes when cold. This doesn't sound the same, but it does give me a bit of reassurance nonetheless. Thanks
Therealsmitty
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So I put in the 0w=30 full synthetic and started it up this morning. The sound is a bit more subdued but it's certainly still there. I'm going to have to hope this is indeed an exhaust issue rather than an engine problem. We'll find out with time and I'll check back here for any other pointers anybody might have! Thanks all
sparkvark
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Have you looked to see if you have rusted off exhaust manifold bolts. My 5.3 has several and makes that sound when cold but goes away as it warms up. It has 401,000 miles on it.
gpd4
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Mine has an exhaust leak at the manifold at a cold start. It's irritating, but it goes away when it heats up.
