I started to get misfires so I began maintenance. I’ve replaced all the coils, plugs, and injectors in my 07 f150 fx4 5.4 And am now getting several error codes including a misfire on cylinders 1, 4, 5, and 8 with random multiple misfires as well as an error saying system too rich as well as an error saying that the o2 signal sensors are stuck rich in bank 1 sensor 1 and bank 2 sensor 1. Any ideas?

 

Yes, but "IDEAS" would probably be the most accurate description of it.

As with all 'codes' - it is a process of putting a bunch of 'ideas' in a martini shaker and rattling them around in your head to see what shakes out - based on what MIGHT be a cause and effect.

An effect of being 'too rich', stated literally is that the PCM has 'shortened' injector pulse widths as far as it can (25 to 30%) - AND TI IS STILL UNABLE TO GET O2 SENSOR READINGS TO COME BACK (DOWN) INTO LINE FOR PROPER FUEL/AIR MIX RATIO. so DTC P0172 &/or P0175.

An effect of 'O2 Sensor stuck high' is just that. Stated literally is that repeated PCM readings of the O2 sensor's voltage level is (HIGH) above .45v. (It should swing above and below .45 volts if injectors pulses are delivering the correct amount of fuel for the amount of air being 'metered' into the intake as read by the MAF sensor).

Now, what mechanical or electrical conditions COULD possibly cause one or the other (or both) those conditions?

1.) You mentioned replacing injectors. What color are they? Are they rated properly (xx lbs at a given fuel rail pressure. Probably 19 lbs)?
2.) Does the exhaust smell of raw gas? Is your Fuel Mileage down, Have you gotten a P0420 or P0430 DTC. --- (YET). This would confirm TOO MUCH fuel is ACTUALLY entering the fuel/air mix - and provide some better direction.
3.) Is the Fuel Rail Pressure TOO HIGH causing a given injector pulse width to deliver TOO MUCH fuel?
3a.) Is the Vacuum reference to the FRP sensor connected / not leaking? (which will make it produce TOO much pressure while giving the PCM a proper 40ish lbs PSI reading).
4.) Is the MAF sensor producing the proper xx Gram/Second reading for the amount of air (ACTUALLY) being aspirated? (Around 5 to 6.5 g/s at idle)
5.) Have the O2 Sensors gone bad on BOTH banks at the same time? (Doubtful)
Each of these 'possible' causes can be checked/verfied, and have to be to avoid shotgun throwing parts at the problem. An easy effort would be to use quality cleaner and procedure and clean the MAF sensor. (I actually DOUBT that is the problem).

But this issue can certainly result in random misfires by having the fuel/air mixture WAY TO RICH - or it could ACTUALLY be backwards from what it seems and be causing the combustion to be way too lean (If both O2 sensors are producing faulty readings).

Just food (IDEAS) for thought. Good Luck

 

Not to bad mouth you, but are you sure the original motor is a 5.4 ?? You will get those codes if you put 5.4 injectors into a 4.6 motor.......... or like F150 said, you injectors are way off rating.

 

Upon further inspection, I’m also missing two of the studs and nuts for my exhaust manifold. If I’m not mistaken, that would allow air to enter the exhaust system which would make sense why my o2 sensors are reading rich. That would tell the computer to adjust the air fuel ratio causing the engine to misfire. Does that sound plausible?

 

Yep. But the extra air (oxygen) could make the O2 sensor for that bank read LEAN ( not rich). And the PCM would then ADD fuel for that bank.


And your random misfires are not consuming the oxygen, and just passing that oxygen on to the O2 sensors, which would also read LEAN.


Now on the other hand, if you put the wrong injectors in, that could make the O2 sensors get stuck RICH (i.e., there is no oxygen in the exhaust for the upstream O2 sensors to "sense".