I can't Kill this backfire and it's driving me BONKERS!!!
AMC 401, warmed over, 454 TBI, Dizzy locked at 0, computer controlled timing, brand new MSD TBI coil, brand new Taylor 8mm spiral core wires, brand new Autolite Copper core plugs (gapped at .0454), New brass terminal Duraspark wide cap, new brass terminal rotor.
My truck runs AMAZING when it is stone cold and going less than 50MPH. If I accelerate to get on the freeway, at about 60 or 65 it starts to backfire out the exhaust. It has been doing this since my rebuild finished (including the installation of my EFI). I have replaced rotor, cap, wires, plugs, and coil. When it is warm, under steady throttle, at 55 or so, it will backfire and run pretty poorly.
1) Could I have a Mechanical engine problem causing this? Cam timing? pushrods too long? obstruction in my intake? leaks out my injectors? Valve issues?
2) I plugged my PCV port for now. I plugged all the other vacuum ports for now, other than trans modulator and brake booster. I watch my MAP sensor and my vacuum is pretty darn steady so I assume I don't have a vacuum leak. Maybe I do?
3) I don't hear any exhaust leaks... My 4 wire O2 Sensor is in my header collector on the passenger side (long tube headers), going to a 3" Y-pipe and out through a single 3" exhaust, no cat, but I do have a Borla Turbo muffler. Could it be an exhaust problem?
I am running out of ideas. I am starting to think I need to pull my EFI and go back to carb... Not sure where to go! This is killing me!!!!
No question/idea is to basic or out of the box. I am not too proud to accept ideas or questions that someone with common sense would have thought of.
AMC 401, warmed over, 454 TBI, Dizzy locked at 0, computer controlled timing, brand new MSD TBI coil, brand new Taylor 8mm spiral core wires, brand new Autolite Copper core plugs (gapped at .0454), New brass terminal Duraspark wide cap, new brass terminal rotor.
My truck runs AMAZING when it is stone cold and going less than 50MPH. If I accelerate to get on the freeway, at about 60 or 65 it starts to backfire out the exhaust. It has been doing this since my rebuild finished (including the installation of my EFI). I have replaced rotor, cap, wires, plugs, and coil. When it is warm, under steady throttle, at 55 or so, it will backfire and run pretty poorly.
1) Could I have a Mechanical engine problem causing this? Cam timing? pushrods too long? obstruction in my intake? leaks out my injectors? Valve issues?
2) I plugged my PCV port for now. I plugged all the other vacuum ports for now, other than trans modulator and brake booster. I watch my MAP sensor and my vacuum is pretty darn steady so I assume I don't have a vacuum leak. Maybe I do?
3) I don't hear any exhaust leaks... My 4 wire O2 Sensor is in my header collector on the passenger side (long tube headers), going to a 3" Y-pipe and out through a single 3" exhaust, no cat, but I do have a Borla Turbo muffler. Could it be an exhaust problem?
I am running out of ideas. I am starting to think I need to pull my EFI and go back to carb... Not sure where to go! This is killing me!!!!
No question/idea is to basic or out of the box. I am not too proud to accept ideas or questions that someone with common sense would have thought of.
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