I have a 2005 Dodge Ram with 5.7l. It started running rough so I had a Mechanic friend put his computer on it. it said that there was a multiple cyl misfire and then showed that the whole left bank was misfiring. what could the problem be?

code is for multiple misfire, have you got the plugs connected in correct firing order ? if have try getting someone to start engine somewhere dark and watch for any Arcing from plug leads , if nothing seen recheck the timing , fuel delivery etc

Have you checked for a broken valve spring. Repaired a dodge engine with the same running issue as you have described and it was a broken intake valve spring.

Usually you get a code that tells you which cylinder or cylinders are acting up.
The code means the cylinder (s) are not providing power but does not tell you why.
So you have to figure out if it is an ignition, compression, or fuel problem to proceed. Could also be a vac leak.

YOU HAVE MISFIRE IF YOU HAVE THE RIGHT TOOL IT MAY SHOW YOU WHICH PISTON IS CAUSING IT GO FROM THERE

How long has it been since the fuel filter was changed?

THIS JUST HAPPENED TO MY 5.4. HAD IT PUT ON COMPUTER TO FIND OUT WHICH CYL'S WAS MISFIRING, AND REPLACED THE COIL PACKS ON THOSE CYL'S. THIS FIXED MY PROBLEM. IT WAS AN EASY FIX BUT EACH COIL PACK IS AROUND 50$, AND EACH CYL. HAS ITS OWN SO THERE IS 8 ON OUR ENGINE NOT A CHEAP FIX. NOT GOOD TO TRY TO DRIVE WHEN ENGINE LIGHT IS FLASHING WAS TOLD THIS CAN CAUSE CATASTROPHIC DAMAGE TO THE ENGINE. HOPE THIS HELPS, AND GOOD LUCK.

sounds like you need an engine my friend or a good mechanic to rebuild that one

did you check to verify that you have the wires in the correct order possible distributor pick up bad

OBD II 300 Random/Multiple Cylinder Misfire Detected

When the misfire monitor detects a misfire, it will trigger the check engine light with the specific cylinder number as the last digit in the P030X code. For instance cylinder 1 misfire is P0301, cylinder 2 is P0302 etc. In this case we have either multiple cylinders misfiring, or the computer simply can't determine the specific cylinder, and as such we are left with the P0300 in computer memory.

Possible Causes:

Fuel injectors, related wiring, sensors and computer issues
Running out of gas, or poor fuel quality
Evaporative emissions system (EVAP) concerns: fuel vapors leaking into engine
Incorrect Fuel Pressure
EGR system concerns: leaking EGR valve or restricted ports
Base engine concerns: low compression, valve train problems and timing issues
Ignition system concerns including, but not limited to:
Faulty spark plugs
Faulty coil or related wiring
Ignition module or related wiring issues
Ignition related sensor faults or wiring issues