confusion of a 99 chevy tahoe

I have a 99 chevy tahoe and it has a random multiple misfire code and a running rich code thrown everytime it has been diagnosed. we have replace nearly everything on the motor just short of replacing the whole engine. we are at a point of not knowing what could cause it to constantly run this way regardless of how much work is being done to it. Does anyone have any ideas what could cause these codes and what the resolution may be? The mechanics we have taken it to don't know what is wrong either. They replace parts they think it causing it to do this and it doesnt resolve anything. Does anyone know if it could be timing or the coil or what because it isnt throwing these codes but everything else has been replaced....:runaround:

1st of all, welcome to the AF.

2nd of all, you need to be very specific as to what parts have been replaced and what code numbers are showing up, both active & history. In order to try and help you we need the code numbers, not descriptions.

I assume you are getting a P0300- random misfire---I do know that cheap distributor caps will cause this--Thus, I only use OEM replacement parts- especially distributor caps and wires.....

New- Central Sequential Fuel Injection Unit-

New rear breaks including hardware- New Master Cylinder

New Camshaft Position Sensor

New Crank-Shaft Position Sensor

New MAP Sensor

New Knock Sensor

New Cap and Distributor

New Water Pump

New Intake Gasket

New Plugs, Wires, Oil Change, Air Filter, Fuel Filter

New Fuel Pump

New Heater Switch

New Aftermarket Exhaust

I dont know the exact code # it just says multiple random misfire and fuel system running rich. It says to look for vacuum leaks but we cant locate any... Do you know where I could find an extensive vacuum diagram other than the one under the hood? Thanks for your knowledge