Z71 not starting, just cranking

[jbabb]

I have a 99 K1500 with the 5.7L. It has been running rough for some time now and I have not been able to trace the problem down. I have replaced the plugs, plug wires, distributor cap and rotor button, fuel filter and pump, and recently the EGR valve. When it was running, it would run very rough off of idle and through all the gears. If you went ahead and pushed the petal down to about 3/4-full throttle the engine would run fine. I got in it today to go to class and it will crank until the battery dies but not start. Every once in a while it will fire one cylinder or a couple of them but not start. I pulled the codes for MULTIPLE CYLINDER MISFIRE and WARM UP CATALYST EFFIECENCY BELOW THRESHOLD and MAIN CATALYST EFFIECENCY BELOW THRESHOLD. Any suggestions? I am getting to the point of taking it to someone, except now it won't start at all.

[getcrunk88]

check your tbi plate to see if it is dirty

[pm26]

The timing chain may have jumped a tooth or two and it is really loose.

 

Is the ignition base timing adjusted properly?

 

Possibly bad fuel pump? Check the fuel system pressure.