Misfire on Cylinder 4 (P0302) and Lean on Bank 2 (P0174)


I purchased it and conducted a mean tune-up (new coil pack, wires, plugs, cleaned the throttle body, etc...). I've searched for vacuum leaks with no success, checked the PCV, cleaned the MAF, etc...


Question: Are these codes related? If so, could it be a dirty/faulty fuel injector (e.g. a dirty injector on cylinder 4, which would affect the fuel/O2 level?...



2001 Ford Ranger Edge 3.0L

***UPDATE***
I pulled the IAC while vehicle was idling, the RPM lowered to 500 and nearly stalled. I no longer suspect a Vacuum Leak. I felt fuel injectors 1, 2, 3, & 4 and noticed a consistent 'ticking' on all injectors but #4 (Cylinder 4)...

Good Morning Y'all,


Issue resolved, cylinder 4 is now firing, NO CODES. It idles (700-800 RPM) and runs exponentially better.


Conclusion: Lean on Bank 2 (P0174) and Cylinder 4 Misfire (P0302) codes suggest a relationship (e.g. air/fuel ratio imbalance and misfire on one side of the engine could be caused [among other things] by a faulty spark plug, plug wire, and fuel injector)

Welcome to the forum

Good work

P0302 is misfire on cylinder #2 which is on Bank 1(passenger side) cylinders 1, 2, 3
Bank 2 is Drivers side cylinders 4, 5, 6

Lean code means computer is having to open the injectors longer than it calculated, engine is never really running Lean

The computer calculates the amount of fuel needed to get the 14.7:1 air:fuel ratio for gasoline, based on RPMs, Throttle position, air temp(IAT), coolant temp(ECT) and air flow(MAF)
It opens the injectors to add that amount of fuel, then looks at O2 sensor
If O2 sensor shows too much Oxygen in exhaust(lean) then computer opens injectors on that bank a little longer, then looks at O2 sensor again
This repeats until O2 sensor shows Oxygen level is correct
And all this take less than 2 seconds, it happens very fast

If computer has to change the injector open time more than +/- 15% of calculated time then it will set a code letting driver know there is a problem with its calculation.

A dirty injector could cause one bank to show Lean, or a failing spark plug, misfire means no Oxygen is burned with the gasoline, so all that oxygen is dumped into the exhaust and O2 see that as Lean.
So you are correct that a misfire can also cause Lean code, but your code 302 doesn't match up with Bank 2 Lean

MAF sensor issue or upper intake vacuum leak would tend to cause Lean on both banks of V6 or V8 engine, but not always.
Low fuel Pressure can also cause Lean codes, computer has no fuel pressure sensor, it is programmed for vehicles expected fuel pressure, and fuel injectors size, and that's what its calculated injector open time is based on

You're absolutely right, RonD. I miss reported the Misfire code. The code reader stated 'misfire on cylinder #4' which is technically a 'P0232'... according to the Haynes manual. It's purring like kitten though

P0301 to P0306 is OBDII misfire codes for a V6 engine, cylinders 1 to 6

Ford OBDII codes seen here: OBD-II Trouble Codes

Rangers used OBDII from 1995 and up

P0232 is "Fuel Pump Secondary Circuit High"

So don't rely on that Haynes manual


OBD = on board diagnostics
This is a "language", a communications protocol
Original OBD use 2 and 3 digit codes

By the mid-1990's a "universal language" was agreed on by ALL auto makers and uses a letter followed by a 4 digit code
This was called OBDII(OBD2) since it was 2nd generation, so early versions are now called OBDI(OBD1)

All vehicles sold in North America had to be OBDII compliant by 1996
Ford changed the Rangers over in 1995 model year

What this means is you can use an OBDII reader/scanner on ANY vehicle, 1996 and newer.

Picture here of what each letter and digit means: https://media.licdn.com/mpr/mpr/shri...ZGZlMGI3MQ.jpg

P codes will be the most common

Well aren't you "Ronnie On The Spot"... thanks for the information, I'll definitely be using the above link in the future

ron is "the wiki of rangers"! :)