1996 tahoe p0300

I have a 1996 tahoe 2 door ive had a ses for about a week and its for the maf and it ran fine last night now this morning it was back firing barley wanted to shift loss of power i took it around the block kept doing it so i brung it back home and put scan tool on it got p0302 miss fire and p0102 i put a used maf that does work and i disconeccted the battery to reset computer fired it back up still did it gave it some gas and now the maf code is gone but i know have a p0300.
I put true duels on it about 2 yrs ago never had any problems and the passenger side bank is running rich/ dumping fuel

Is your scan tool capable of reading live data from the ECM? Checking your MAF airflow, O2 sensor crosscounts, and live misfire data is the absolute best way to narrow this issue down to a specific part or cylinder.

The possibilities include, but are not limited to: fouled spark plug or plugs, plug wires intermittently grounding out or crossfiring, distributor cap failing and crossfiring (common), bad injector poppet, failed FPR leaking fuel (explains rich passenger side bank), failed O2 sensor causing skewed fuel trims on one bank (scanner would confirm/eliminate this), partially plugged catalyst (though I assume you have removed them ), low fuel pressure (common on these trucks, and the injection systems act strange with borderline low fuel pressure), vacuum leaks, ECM and ECM wiring faulty or failing.

Bottom line is you need live data to narrow down the issue to a specific component. And you need a multimeter to verify power, ground, and signal voltages if a sensor is suspect.

In addition to what SAATR already said: Is your scan tool capable of displaying cylinder-by-cylinder misfire codes and misfire counts?

I hate seeing people report a P0300 code; the usual issue is that the scan tool they're using is LYING to them. The real code is often cylinder-specific, but cheap 'n' crappy scan tools report "Random" misfire.

In other words, is the real code P0301--P0308?

This gets cleared-up in a hurry when a tool that can show misfire history for each cylinder is connected.

My scan tool does not give cylinder by cylinder but p0300 went away and p0302 and p0102 came back. I should have mentioned its got the mpfi upgrade, new distributor, cap rotor cam sensor. All 4 02s are new. Yes cats are gone never had problems or ses from removing them. Maf rate at idle is 1.3 - 1.4 lb/ min
i noid light tested all the connectors on the harness that plugs into the spider (mpfi conversion) all flashed consistantly. Fuel pressure drops instantly after the pump is done primeing but holds at 51 when running.

I wrote down all info i thought would help that my scanner gave me

Fuel pressure dropping "instantly" indicates one or more of three possibilities: 1. Leaking injector(s), 2. Leaking fuel pressure regulator, or 3. Leaking check-valve in the fuel pump.

I just went and did another fuel pressure test just to be sure when priming 60 pounds when it stops primeing pressure drops imediatly to 0 when running holds at 51/52 pounds

I did the mpfi about 2 and a half years ago and this past aug i did fuel pressure regulator because it was missing p0300 and i did find fuel on back of intake but it wasnt it it was the distributor thats all new this past aug most liklely both were the prob. But idk if its common for fpr's to go bad or if its common for the mpfi to leak after 30k miles. But the maf p0102 i had for about a week and then yesterday morning p0302 came would the maff code correlate to the p0302 at all?

Im not doubting its a injector or fpr but im having a hard time seeing its either of them because there both new/ the better mpfi.

Is the check valve in the pump or sending unit? All mine is new from about 2.5 yrs ago i only put about 30k miles on it

On the 2 door i did mine and the pump i replaced with out replacing it and my brother just did his on a 99 gmt400 pick up same 350 vortec but he had to replace the whole unit as he couldnt just do pump

I have a vid of passenger side bank tail pipe and raw gas is coming out but it wont let me post it its too big of a file