Have a 1989 extracab 2x4 pickup with the Z24i 4 cylinder, 8 spark plug engine, 5 speed trans. with high mileage. It seems to misfire and has occasional backfiring in the exhaust when accelerating between 1500 and 2600 rpm. It runs great above 2800 rpm with no apparent sign of the lower rpm "problems". This now occurs more when the engine is warmed up a little - no such symptoms during first 3 miles when starting out from cold (say 10-30 degrees ambient temp. at 5000 feet (Denver, CO area)). I have replaced the distributor cap and rotor and "new" Chinese ignition wires. New air filter and NGK intake spark plugs. Cleaned and re-gapped exhaust spark plugs since parts supplier didn't have right NGK exhaust spark plugs. Replaced intake ignition coil with a used one from my parts truck. Also checked for vacuum hose leaks. Checked battery connections and replaced the 2 short wiring links (1 is fusible link?) at the battery. Each "fix" seems to help for a little while, then back to misfiring. WHAT WOULD YOU TRY NEXT? I haven't checked compression (HOW? - on intake side only?) nor fuel pressure (don't have a Proper gauge for 30 - 40 psi -- suggestions as to where to get an accurate one that can read while driving?) I am wondering about the distributor- does it have a Hall-effect sensor? Also, could change the exhaust ignition coil with a used one from my parts car. Fuel filter and pump and loose wire at ignition switch don't make sense since it runs well when starting out and at 3000+ rpm, BUT??? Since there is some slight temperature effect, also how about swapping the air filter housing (using the one from parts truck)? I also once read about some kind of fuel injection system "handoff" in the 1800-2400 rpm range, but think it was for another vehicle.