View Full Version : Snapping noise from under car

04-28-2009, 12:06 AM
So I just finished a head gasket replacement on the car, and I was in the process of idling it to circulate some new oil to clean out the oil pan (gonna do another oil change in a day or two) and I gave it a little bit of gas to help out the idle and there was a loud Snap or Pop from under the car, about where the manifolds meet the exhaust pipes. At first I thought it was just a backfire, cause by old gas or something, and I put some new gas in it and it did it again. It only pops when you sharply tap the gas. It seems independent of RPMs. It doesn't sound like a backfire, more like hitting a piece of metal against another, except without as much resonation.

My only thought is the exhaust flange isn't tightened all the way and I'm hearing a sudden shift of the joint between the exhaust manifolds and exhaust pipe. Sound like a possible cause to you?

04-28-2009, 08:02 AM
I would make sure your exhaust mounting points are secure. This includes making sure you have a good seal between the exhaust manifolds and downtubes. Do you hear any ticking noises? Also, have you checked your motor mounts for sagging or tearing?

04-28-2009, 09:09 PM
I haven't noticed any ticking. I haven't checked the mounts but I guess that if they're bad the engine will be rocking a little more. I tightened the exhaust flange a little bit too, and I made sure they were even but it still made the noise, but I'm not sure its as tight as it needs to be. How hard are they to change?

04-28-2009, 11:06 PM
Anyone? I am really confused. I checked exhaust manifolds and they seem very secure. I don't know if its a backfire, I haven't heard one in a car newer than 1985. If its a backfire I need to know whats causing it before I can take it in for Emissions. I'm not getting any trouble codes or check gauge light. :confused:

Previously, it only did it when i pressed the gas sharply. I noticed I had lost a screw on my hose clamp on the throttle body so I just replaced that, and now it idles a little bit better, but when I first started the car, it had trouble going and it made the sound when it was coming back from the rough idle, when I revved it slower, it also did it once the boost started to build, and the boost gauge sorta responded to the sound. I don't know if thats related to it or if its just responding to the sudden vibration.

When I did the head gasket, my EGR tube broke, so I put a block off plate and a gasket on the intake manifold, and also a flange fitting on the exhaust manifold until i can get it fixed. It seems like the exhaust manifold is leaking after I let the car warm up. Could this cause the backfire? I also didn't check the valve lash when I put it back together.

04-28-2009, 11:18 PM
Can you hear it in the engine bay or only when you're driving it? If it's only happening when you drive it, it could be you bushings.

04-28-2009, 11:24 PM
Ok well I fell like a major [email protected], but its fixed now. I didn't think it was the case since the car was idling pretty good, and I figured it wouldn't work if the firing order was wrong, but it turns out that was it :-) Someone suggested it to me earlier, and I did a search "backfiring" and it brought up a post where someone had done the same thing I had. So its fixed now. Just firing order. Turns out the car is fine, the only flaw was me hehe.

04-28-2009, 11:36 PM
i don't think that will cause a backfire by itself. you might want to take another look at that connection you kinda threw together. other then that ..don't know

04-28-2009, 11:40 PM
well it might not have been a backfire i was hearing, but thats what a few posts i saw said. anyway, i started it up and its doing wayyyyyy better now, no backfire, no rough idle, no missing.