reacquiring check engine light : code p0305

Question

my 2000 Chevy Z71 Tahoe 5.7L has 154,700 miles and @ 70 mph i get vibration for about 4 seconds and then check engine light comes on and stays on for about 24hrs and then goes off until i exceed 70 mph again, have had since brand new and have always maintained quite well engine code is p0305, misfire #5 cylinder. have changed & replaced w/new:

1) ac/delco generation 2 fuel injection spider kit (plenum gasket, throttle body gasket etc.)
2) ac/delco generation 2 fuel pump.
3) ac/delco plugs.
4) ac/delco wires
5) new coil.
6) new distributor cap & rotor button.
7) new mass air flow sensor.
8) new fuel filter.
9) new ac/delco gas cap.
10) complete carbon clean out on plenum, throttle body & intake valley.

engine runs quite well for 154,000 plus miles and even better since new fuel injection spider & fuel pump, have changed oil every 3,000 mile and fully maintained motor.

any suggestions? would like to repair as every option still works on this vehicle as i use as work vehicle.

Answer 1

You can rule out what is not the cause, A leaky fuel pressure regulator will not only affect 1 cylinder but all the cylinders , A faulty distributor will cause a cam and crank correlation so a distributor is unlikely,A parial plugged exhaust this will cause random misfire, You code only one cylinder this is more a mechanical fault where the intake valve and exhaust valve make have a crack.A leak down test of the cylinder will find the fault. G.M products tend to code a particular cylinder at fault when there is a misfire, and it tends not to be that cylinder .