misfire/backfire help!

[brianGTP]

I have myself a 97 gtp running a XP cam and I just recently installed speed daddy headers and after the install I cranked her up to make sure all was good and I noticed it had little misfire here and there. today I drove it around the block and noticed itll back fire under a good amount of throttle. never had this problem with the stock manifolds so im a little confused. I thought it could be the zzp 10.5 mm wires so I put the stock wires back on but still the same problem. everything I have done: xp cam, 105 valve springs, double roller timing chain, ngk tr6ix iridium plugs, zzp 1.0 pcm, shorter dog bones, 3.4 pulley, speed daddy headers, EGR block off plate on headers only( letting the egr tube suck in air with a small filter on the end), zzp 10.5 plug wires( running stock ones now).

[Fivefingerdeathpunch]

You must block off both side of the EGR tube.

You are making a huge vacuum leak having the one side open.

[brianGTP]

ok that's a easy fix. also my downpipe is not connected all the way because one of the bolts broke so the down pipe isn't completely sealed so it makes that backfire very noticeable, and under acceleration it feels powerless. my thought was that there isn't enough back pressure with the downpipe pretty much open. but im getting it fixed in the morning

[dsmuts]

You don't need back pressure. You need to fix your vacuum leak at the egr and the exhaust leaks

[BillBoost37]

Sounds like he has the EGR hooked to the lim. It can't suck in any more air than would be forced through with the pressure of exhaust behind it.

Did you pull the plugs when you did the headers? If not..fix the cracked plug.

[Fivefingerdeathpunch]

Re-read the first post Bill.

Then you'll figure out why its a huge vacuum leak.

Hint hint, the second to last line.