I have had this muffled pop under the hood after getting on the throttle to merge with traffic or this past weekend when I was pulling a trailer. It only happens right when I let off the gas after accelerating hard or get up to speed with the trailer. It is just one single pop, no missing or rough running. It doesn't happen when I take off normally from a stop. No work done on it lately, the last thing was a tune up several months ago, plugs, wires, cap, and rotor. It just passed emissions inspection last week, it runs fine other than that pop. Any ideas where I should start poking around would be greatly appreciated!

 

Will it do it in neutral, in your driveway??

 

Hey You, I have never heard it pop while revving it in the driveway, but I never have really gunned it hard in neutral. I will try it and report back.

 

No pop when in neutral. I put it in gear, foot on brake and revved it, still no pop. I drove it around the block and with a hard acceleration got the pop. It sounds like a muffled backfire under hood.

 

Plenum? Perhaps the fuel sync is off?

 

I haven't done the plenum and there is oil on the plate when I looked in it. If that can cause the pop then that's probably it.