Mwyatt23

when throttling the engine to 3000 rpm and letting off the gas, "backfire" big time.

mattdel

Backfire while the engine is decelerating is usually a sign of a stretched timing chain.

Mwyatt23

Brand new engine...not even a month old. Everything should be tight

mattdel

Sounds like maybe you have a dead MAF ? Choices are closing down to a select few.

Mwyatt23

Well it seems to be working too, unplug it...and the car dies.

mattdel

Just for giggles, find a known good coil you can swap out with. With everything you've replaced, its either gonna end up being something internal like a cracked valve spring, or one of your replacement parts was bad out of the box. Computer, coil, and IAC are most likely given your descriptions of the various symptoms. Maybe even a single bad spark plug.

Run codes on it, then do the cylinder balance test as well. That could help narrow down electronic or internal. http://sbftech.com/index.php?PHPSESS...d&topic=2471.0

duncan01

Is your mass air calibrated for you injectors? If not it can cause a pretty nasty lope cause your air fuel will be off...

Mwyatt23

How do I calibrate it?

mattdel

Explaining how it works is rather complicated, but basically any aftermarket MAF will have a certain calibration to it so that it reports the proper readings for different sized injectors. It's something that you'd know beforehand when ordering bigger injectors or an aftermarket MAF, as they're all labeled as such when you buy them. Even with a stock injector set, if you have an aftermarket MAF it must be calib'd for 19# injectors. The stock MAF doesn't really have a calibration built in, it's the ECM that calculates it all, so the "calibration" of aftermarkets is really just tricking the ECM.

Either way, it's not something you can actively calibrate on your own. You'd either have the correct parts and not need to, or you have to go visit a dyno tune shop and have them adjust all the fuel curve values, which is usually something reserved for quite high performance applications. With proper parts, the foxbody ECM can adjust itself very well, up to a few hundred HP.

craig71springsport

Have you replaced the fuel pressure regulator? Sounds like a possibility. If it stays running at what I'm assuming are RPM's above 1500-2000 on the highway, and at 3000 RPM revs. At idle when you have to give it gas to keep it running can signify the engine starving for fuel. I don't think that you wrote down that you replaced the FPR, did you and just forget to write it? If you didn't that would lend this possibility more credibility.

That's not to say that it couldn't be anything mattdel has suggested, as what he has said could be wrong are all equally viable possibilities. If it were my car though, I would price a FPR and replace that soon.