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Backfiring after header install help!

Old 1/10/19, 12:56 PM
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Backfiring after header install help!

If anyone could help me with my issue that would be lovely. I decided to change the exhaust manifold on my 99 mustang from stock to shorty headers and x pipe. l also in the process did an egr valve delete and installed a cold intake. The first time and i started the car it ran fine but sounded like it was off so i checked the wire placement and re-did it and started it again and didn't want to start. than went back to original wiring and started right up but still sounded off. But than when i went to test drive it afterwards it started to backfire which sounds like pops but only when accelerating and decelerating. But at idle it seems to have a hanging idle and idles around 6-7 k. Also when putting the car into gear(automatic) it seems to bog down when under-load and the rpms drop to 5k. I have also seen that my fuel economy drop because i have to fill it up every two to three days. I think the car needs to flashed. Can anyone help? Only car.
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Old 1/11/19, 08:51 AM
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possible vacuum leak. Check all your air intake connections and the seal on the egr valve
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Old 1/11/19, 10:24 AM
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the new headers i put on dont have a connection for the egr so i deleted the egr. Would deleting the egr cause the backfires along side with the high flow headers and x-pipe?
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Old 1/11/19, 12:11 PM
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How did you plug where the EGR connected?
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Old 1/11/19, 01:10 PM
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I just used a block off plate with a gasket. Im waiting for a flash tuner so i can turn of the egr system and tune the car because it is running really rich.
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