Code po304 cylinder four misfire on 1999 ford explore sport fuel injected 4.0 litre 2wd

P0300 random misfire, p0302 cylinder 2 misfire, p0304 cylinder 4 misfire, p0411 secondary air injection system incorrect flow detected, p1296 cooling system malfunction

Code 300 is a random miss not serious enough to peg a cylinder, code 302 is for cylinder 2 and code 304 is cylinder 4. Code 402 is for an EGR flow problem.
Its possible the EGR problem is causing the missfires. The computer sets the 300 codes when RPM drops on a cylinder. The computer does not know why. So it could be spark, fuel, compression, or a vac leak.

Faulty sparkplug wire or injector.First check the injector harness a poor connection on the number 1 cylinder then i would replace the plug wires and have the injectors cleaned.

PO304 --is a misfire on cylinder # 4
The 171 is an O2 code from the misfire

Care to say what vehicle you have!

ITS YOUR FUEL PUMP IT DOSE IT WHEN YOUR ON THE GAS MOSTLY ON UP HILL CONDITIONS THE PUMP IS STILL WORKING BUT ITS NOT PUTTING OUT ENOUGHT GAS UNDER LOAD CONDITIONS PO304

PO300 AND PO301 AND ENGINE MISFIRE CODES FOR #1 CYLINDER I HAVE A 96 BLAZER I GOT PO304 WITCH IS #4 CYLINDER IT TURNED OUT TO BE THE FUEL PUMP WASN;T SUPPLYING ENOUGH FUEL I REPLACED IT FIXED THE PROBLEM BUT ITS KNOT CHEAP TRY REPLACING FUEL FILTER LOCATED UNDER DRIVERS DOOR MOUNTED ON FRAME GOOD LUCK YOU REALLY DON;T WANT TO SCREW WITH THE FUEL TANK AND LINES ON THIS VEHICLE

Do you have spark at the number four cylinder? Check that if spark is present , then you should swap the injector from four to five and see if the miss goes with the injector. If not then you will need to test the engine compression .

Misfire detected in cylinder 4.

If the vehicle has a lot of miles since the last tune-up, it may be time for one.

If that is not the cause, it can get complicated and a repair shop should look at it.

might be the coil pack is bad, wires, plugs, o2 sensors, dirty injectors, catalic converter ( only if you smell rotten eggs ) . cylinders are misfireing.

complete tune up plugs wires distributoe cap and rotor