1999 Tahoe bad misfire

[1loudho]

soooo, i have been dumping money in my hoe non stop lately to try and fix this problem and nothing has worked, so far i have done the following: cold air intake, dual exhaust (first 2 things i do to every vehicle), plugs, wires, coil, cap and rotor, switched over my fuel injection from SCPI to MPI, fuel pump, fuel filter, throttle position sensor, 195 thermostat. After ALL that it still stumbles and did i mention i am getting 7-8 mpg WTF!!!! let me explain, when i am driving at a constant speed it is real noticeable like on the freeway but if i am romping around in town its not that noticeable also if i drive at 45mph then drop it down a gear and the rpms jump up it gets real bad and starts to spit and sputter and back fire. PLEASE HELP ME!!!! i am about to put a rag in the gas tank and watch the fire works because i am so frustrated

 

[zomeizter]

You must have installed injectors in wrong cylinders, the symptom points to that directly.

 

[AZ Tahoe]

Second that

 

[SouthernHoe]

And make sure its timed correctly. It sounds like mine after I rebuilt the motor before I realized it had to be put on a computer for timing.

 

[1loudho]

it was doing the misfire before i did the MPI that is why i did it, why would timing be off if i never messed with the distributor??

 

[Kon99]

They only other thing I can think of that hasn't been mentioned or replaced is the pump. Could be that, or maybe somethings wrong with fuel lines?

 

[1loudho]

pump has been done already, i heard someone say the lines might have a pin hole that is sucking air could that be without a leak???

 

[Phone Man]

Try cleaning the MAF and Throttle body along with the IAC

 

[Kon99]

When you replaced the cap and rotor, did you replace the distributor shaft as well? That is also a possibility.

 

[Dowsewashere]

Timing. And are you 100% your plug wires went back on correctly?