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Good morning to all. I have an issue, that has arisen recently, in that upon throttle release and/or when throttle closed or when coasting down to a stop (say, 2nd gear down short hill to stop light) my 2000 Supercharged LS1 w/6speed has developed a nasty "pop" and/or "backfire"! It is, to say the least, embarressing and cannot be good for my beloved corvette. It has been tuned by a qualified tuner and did not have this issue. This is a recent thing. I own both a tech2 and HPTuners Pro but cannot figure this out. Thank you.
I probably can't help except ask; did you make any changes before this started?
Not ANY changes. What happened was a lady ran stop sign and hit pass side rear. It was in rehab for 3 months and when I began driving it was doing this. I know it sounds crazy but that is how it happened.
Since this happened after you got your car back from repair, I would think that possibly something happened to your exhaust in the accident. Did the repair shop do anything to your exhaust system? Anything replaced or had to take the system apart in the process of repairing the rear? It is possible, as already mentioned, that the accident moved/loosened the system or created a crack that is causing the symptom. I would not think it would be a tune issue if it did not do this before the accident assuming it's been tuned some time ago and it has been driven throughout the year and never had the issue.
Seasons can be an issue on having no or some pop in the exhaust. Winter, I do not get much pop on decel, summer it pops like crazy in my car.
If you can't find the issue but want to get rid of the problem, you could use an aggressive DFCO routine in HP Tuners to get rid of it. That would be the easiest and quickest way to get rid of it. Mine does the same thing after the full exhaust swap, I was going to tune it out but then I was enjoying it too much so I left it there. Pops like crazy, but I like it.
I also suspect an exhaust leak between the head(s) and the upstream O2 sensor(s). Air (oxygen) getting into the exhaust there will be seen as a "lean mixture" condition by the computer, and the computer will add more fuel. Since the oxygen is leaking in, not coming from incomplete burn due to incorrect mixture, it doesn't matter how much additional fuel is added, it will never "use up" the oxygen leaking in. But having oxygen plus unburned fuel in the exhaust will cause backfires, "pops" and "burble" as you coast.
Confirmation would be higher fuel trims in the OBD-II data streams, along with the O2 sensor reading on the "lean" side for the average.
Also check from your air box to the intake to make sure you are not getting any unmetered air into the system. From time to time my connection just after the AFM slips apart and my car idles a bit different and pops on decelerations.
This is the classic exhaust manifold leak. You suddenly close the throttle plates, the engine goes to high vacuum and unburned fuel mixes with air and it makes a lot of little popping noises or a few big ones. Check the torque on your exhaust manifolds and inspect the exhaust system carefully.
Thank you to all for the info I know it only started after the accident. The other vette drivers and I are always going sonewhere and they had never mentioned it to me pre-accident either. I was thinking the accident did something to the exhaust as well but wanted your opinions. Thank you again.
Exhaust "pop" or "backfire"
