Can someone please explain....

[Chargerdodge9]

That loud popping sound that I hear sometimes on Orion VII CNGs? It's not the typical backfiring noise that you hear when the driver take their foot off the gas. It's more like when the bus is at a low crusing speed, I would sometimes hear like a small but loud explosion (I assume from the exhaust pipe).I was on #2590 yesterday and it was producing that noise.What is that sound and does it occur on the C40LFs and C40LFRs too? Could it be the Cummins engine? I know that the MTA Orion VII CNGs (DD50G EGR powered) never used to do that when I lived in NY.

[Chargerdodge9]

I was just wondering what that is.

[C40LF_2464]

I forgot what its term was back I say its the backfire. When the driver removes his/her foot from the accelerator it will make that sound. All CNG buses do it. Some of them do it quiet some of them do it loud like our 2500's. MTA's CNG Orion Vii's do it, but not as much  as WMATA's

[Chargerdodge9]

You mean that small popping noise? Or are you talking about the CNG typical backfiring noise?

[NewFlyer9736BCT]

I think I might know what you're talking about. Assuming we're talking about the same popping noise, I know some of Ride On's C40LFs do it VERY loud sometimes.

[Chargerdodge9]

Yeah, it may have to do with the Cummins C+ gas engines. If I'm not mistaken, I believe that the Ride-on C40LFs are also powered with this engine. I also noticed that ART's Nabi CNGs produce this sound too.