smithers

Hey guys! If anyone can help or give me some advice I'd be very appreciative. I've already dumped a lot of money into this thing and I'd like to actually figure out the issue. So anyways codes are as follows now: p0300 p0402 p1345 p0740 P0452. I know the last two have really no effect on this but figure it wouldn't hurt to give all the info. Whats been replaced: Injectors switched to MPFI (Gaskets for intake too), Plugs, Wires, Rotor, Distributer cap, coil pack, PCM, 02 Sensors(upstream). It misfires and has no power what so ever, before this issue it would smoke the back right tire off, now you have to put your foot down to get up and going. The exhaust REEKS of unburnt fuel but all of my wires are putting spark through to the plugs, the plugs have been replaced twice and are gapped correctly. Shop I took it to said cylinder 2 and 8 are the ones misfiring. This is really my winter/towing vehicle as well as hunting mule its extremely clean and has had the engine replaced ~30k on new one now 260xxx on chassis
1998 1500 5.7l Z71 Extended Cab

Rammer75

We had same problem on 99 Suburban K1500 with 5.7L . Kept getting misfire on 2 cylinders after a complete tune up. Problem was fixed by going to AC Delco spark plugs (made by GM). No other plugs would work. We had no more misfire codes or engine light trouble after that.
Good luck to you!