i have an 87 mustang and when i am at idle if i hammer the gas to hard it backfires and pops but if you are soft till about 1700 rpm's after you can hammer it and its fine there is no mass air flow censer on this car i just did a auto to 5 speed swap could the computer have anything to do with this?
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Could be a lot of things, but I figured out what my problem was. I too have an 87GT, speed density. Ever since I changed out to an off road H pipe, and I ran the car hard, it would backfire really badly between shifts when i just had to let off a bit before next gear. Tried everything in the book. You know what it was? Well, I've by passed my smog pump, and problem fixed. The damn pump was still introducing fresh air into the H pipe. As I have no cats, it was not only useless and not needed, but it also mixed in fresh air into the exhaust pipes, and that mixed with unburnt gasoline during WOTs would cause my car to backfire through the mufflers. Once I've bypassed my smog pump, no more backfires. My timing is at 14 BTDC with 89 octane. Runs wicked, wicked well and no more of those damn backfiers during hard runs. Hope this helpd.
