Hello, just put a5.7 in my. 91gmc Sierra.it had a 4.3.i have no fuel. Or spark. Changed the computer to standard 1227747.do I need to change the whole wire harness to get it to start?

Is it a TBI or vortec 5.7 and was it a TBI or vortec 4.3? Best way to go about swaps like this is to either slap a carb on the new engine or have a complete wireing harness and computer attached to the new engine.

Thanks for the reply. They were both tbi motors.

Its odd your not getting spark or fuel. TBI motors are fairly simple. Spark is simply a matter of power to the coil and the distrubutor turning. Fuel is just about as simple. Computer can make it run like crap bit the basics should be there. Check basics like grounds and if the fuse box and relays are getting power like they should. If i remember right the TBI harness was pretty much the same on the 4.3 and 5.7. One i think had an additional knock sensor but other than that.