rang-a-stang
09-05-2019, 08:00 PM
AMC 401, warmed over, 454 TBI, 16197427, $0E, 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. I started with BMHK bin, made some minor changes and run the stock VE and timing tables. Then I tried to lean out the VE tables a little, back the timing off a little, and no change.
1) Could I have a Mechanical engine problem causing this? Cam timing? pushrods too long? obstruction in my intake? leaks out my injectors?
2) How do I look for issues in my data logs? My oxygen sesnor readings swing like they should be (I think??) my timing looks smooth and where it should be...
3) I plugged my PCV port for now. I plugged all the other vacuum ports for now, other than trans modulator and brake booster.
4) 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.
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!!!!
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. I started with BMHK bin, made some minor changes and run the stock VE and timing tables. Then I tried to lean out the VE tables a little, back the timing off a little, and no change.
1) Could I have a Mechanical engine problem causing this? Cam timing? pushrods too long? obstruction in my intake? leaks out my injectors?
2) How do I look for issues in my data logs? My oxygen sesnor readings swing like they should be (I think??) my timing looks smooth and where it should be...
3) I plugged my PCV port for now. I plugged all the other vacuum ports for now, other than trans modulator and brake booster.
4) 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.
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!!!!