Getting a weird "popping" sound when coming to a stop
05-03-2013, 06:07 AM
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Getting a weird "popping" sound when coming to a stop Hopefully someone can help me here, I've had no luck on other forums so far.
In my Blazer with the 5.7 Vortec Gen 1, when I come up to a stop after cruising for a few minutes, it does this weird popping thing which sounds like someone is hitting a hammer against the passenger firewall. It's almost like a backfire but it doesn't seem to be coming out of the intake or exhaust, the sound stays right at the firewall. Sometimes it will do this 30 seconds after I'm stopped. It stays if I rev the engine and increases with RPM.
Nothing looks to be weird using the standard log settings on HPTuners, all of the graphs stay steady, no knock showing on the knock sensor. The first 1,000 miles on the engine were fine and it didn't do this, then one day it started. Switching back to the stock tune for the engine doesn't help. I'm lost.
Is it possible that the valves are misadjusted? I think I'd notice that more distinctively though. Maybe something is wrong with the way I built the motor? You guys really seem to know your stuff in here, I'm looking forward to hearing your ideas. Thanks.
In my Blazer with the 5.7 Vortec Gen 1, when I come up to a stop after cruising for a few minutes, it does this weird popping thing which sounds like someone is hitting a hammer against the passenger firewall. It's almost like a backfire but it doesn't seem to be coming out of the intake or exhaust, the sound stays right at the firewall. Sometimes it will do this 30 seconds after I'm stopped. It stays if I rev the engine and increases with RPM.
Nothing looks to be weird using the standard log settings on HPTuners, all of the graphs stay steady, no knock showing on the knock sensor. The first 1,000 miles on the engine were fine and it didn't do this, then one day it started. Switching back to the stock tune for the engine doesn't help. I'm lost.
Is it possible that the valves are misadjusted? I think I'd notice that more distinctively though. Maybe something is wrong with the way I built the motor? You guys really seem to know your stuff in here, I'm looking forward to hearing your ideas. Thanks.
05-03-2013, 08:19 AM
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The mounts are all firm, I remember looking at it last year for any clearance issues with the headers and other stuff thinking maybe something was loose and hitting. It all looks fine to me.
Something with the exhaust does make sense. It is a totally stock rebuild, nothing fancy. It does have a roller cam so I wouldn't think the cam is flat. I've got 5,000 miles on the engine since it was built. I only replaced piston rings, rod, main and cam bearings when I got it. Cylinders were only worn .001". That's after it was honed. Maybe I'll pop off the valve covers and try adjusting the valves again or something.
Could a bad lifter do something like this? I think that would be a little louder and more of a constant sound though.
Something with the exhaust does make sense. It is a totally stock rebuild, nothing fancy. It does have a roller cam so I wouldn't think the cam is flat. I've got 5,000 miles on the engine since it was built. I only replaced piston rings, rod, main and cam bearings when I got it. Cylinders were only worn .001". That's after it was honed. Maybe I'll pop off the valve covers and try adjusting the valves again or something.
Could a bad lifter do something like this? I think that would be a little louder and more of a constant sound though.
