Backfire

Hey all;
Ever since I installed my ported TB the car has been back firing... The main time it does it is when I downshift. I rev match and punch it into gear and it'll back fire every now and then. It also did it earlier today when I pulled out of a gas station really quick bc of traffic. As I was about to shift to 2nd, it back fired. Plugs, wires, and coil pack are good. I've checked. It's been doing it since I put the TB on for sure. It was fine before that. Only happened maybe once a month or so. Any ideas here?

well you have to be running pretty damn rich to backfire. You probably have a vac leak somewhere on your throttle body. Air is getting out. Have you checked all the vacuum connections?

I've checked but I can't find any leaks. When I'm driving I hear a hiss, sounds like a turbo, and I can hear it get higher as the rpms rise and IM pressure goes up.

yep you have a leak somewhere. Try putting some soapy water in a spray bottle and spray it all over your throttle body. It will bubble if there is a leak. Do this while the car is running. If you still can't find it, built a boost leak tester, heh.

Ha ha, boost leak tester on a NT car...

Maybe a shitty gasket? Did you put in a new one with the new TB? Did you torque er down good?

I got a new gasket when I did the TB. I didn't torque to specs, but that SOB is on there good. I'll try the soapy water thing when I get a chance.

So, what is the science of this? Why would a leak at the TB cause it to backfire?

If you crank it down instead of torquing it to the spec then you'll ruin the gasket and get a nasty leak...

you could have put hte gasket in backwards...mechanic that did my TB and diagnosed my bad idle was cause i installed the tb gasket backwards.. all in all a new TB fixed it lol

you could have put hte gasket in backwards...mechanic that did my TB and diagnosed my bad idle was cause i installed the tb gasket backwards.. all in all a new TB fixed it lol

You cant on the 420a. It only fits one way. It has such an odd shape design to it.

I dont exactly know what I am talking about but its the only thing that makes sense to me. Back firing happens when there is a lot of extra fuel and not all of it burns and gets into the exhaust manifold where it then combusts. Well, the only way you would be getting a lot of extra fuel is by some of your air leaking off, hence the "nonturbo boost leak". I dont know if I am right, but like I said thats what makes sense to me.