what causes a gun shot sound?
 

I am working on a friends car and it makes it very very loud sound, it like a .45 caliber going off. any ideas? The fuel was low in the gas tank to where the light went off.

under what conditions is it occuring?

hah, a buddy of mine would drive in front of a crowd in his old fb while it was cold, rev the sucker up and let go of the gas.
Sounded like double barrel

It'd only work a couple of times until the engine warmed, letting the gas burn first before being shot out the exhaust

The sound occurs under lite throotle right around 3,000 rpms, sometimes it will fire mutilple times, it is so loud is scary...people come out of there house thinking its a adrive by shooting...I have never seen this before, unless a the track and those car are WOT before launch..what could this be..The only thing I found a miss was the TPS was out of range, I corrected that, problem still exsits, and it feels and sounds like it not running right.

I would say crossfire. check Plug wires. If thats the case very bad for apex seals

Nope checked that, pulled the plugs and cleaned them up and she runs perfect now.

Thanks

... lol really... it was just your plugs?

Yes really! I don't understand it, but the plugs were a little fouled, I soaked them in gas, sprayed them down with carb cleaner, did a little cleanning with 200 grit sand paper, sprayed again, ....car ran awesome. spun all of 1st and 2nd gear, with 16" tires. with 140,000 on the clock..no smoke whatsoever. This is true.

Weird...one of my first thoughts was the ACV AAV (air control valve anti-afterburn valve), which sends a bit of air into the intake when you snap the throttle shut. The other thought was the throttle body dashpot, which slows down the throttle plates near the closed end.

edit: I guess the spark plugs weren't burning the mixture well enough, causing unburned fuel to get into the exhaust.

It would have been impossible for those parts to cause the problems as they are both MIA..Thanks so much for the input, I still find it hard to swallow that dirty plugs was the cause, the sound was so fxxing loud, it scared my wife to where she jumped about 1 foot off the ground, she thought someone got shot..lol

but just more knowledge for our club community

Rock on RX7 Club!:icon_tup:

I can do that on demand with my 88 Vert... Along with a james bond style smoke screen... lol Mine actually does it more when it's warmed up< but I have to do it intentionally usually, the smoke occurs over 6000 rpm. When the back fire occurs I get rather large flames out both pipes.. No Cats, no emissions... I think I get about 13-14 miles to the gallon... My theory on the back firing isit is WAYYYY out of time. and the smoke/oil, from what I understand it is my oil control rings.. Time for a rebuild anyway...

Where is this anti afterburn valve at? any photos?