Quote:
Originally Posted by MikeM6
I've noticed that my exhaust sounds deeper/louder at the end of the cold start cycle (after the revs drop to normal idle) for a short period of time, maybe 10-20 seconds. Then I hear a noise, possibly a valve or actuator, then the exhaust sounds quieter/normal. I originally thought this was the exhaust valves closing, but after watching the valves I confirmed they remained opened the entire time. Stock tune.
Has anyone else experienced this? Or is anyone able to explain what is happening during the cold start process that causes this difference in the exhaust sound?
Thanks.
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I know exactly the sound you're talking about. Apparently after the cat warmup higher-RPM period, there's another period of about 10-20 seconds where the A/F ratio and/or the ignition or valve timing is different, and it gives the exhaust a deeper sound. Perhaps someone more knowledgeable in the startup engine management algorithm could tell you more precisely what's going on during that period, but something is definitely different. Doesn't do it on a warm start ever.