Ford Mustang 2004 V6 3.8L OBD codes P0461 P0316 P0303


New Member
Mar 6, 2019
Hello broke college student here that would rather learn how to fix a car than take it in.

odometer: ~135000

04 convertible mustang V6 showed p0461 OBD code initially just causing the gas gauge to fall to empty only on the last quarter tank. I just filled up at that point and left it.

P0316 and P0303 showed up after i experienced a loss in power and rough idle. I replaced the spark plugs, wires and even the coil pack. Problem came back so i replaced the MAF sensor. and it came back again. I then replaced my fuel injectors and the car ran fine for about 200 miles before the problem came back and almost worse. Complete loss of power when going uphill its embarrassing (barely pushing 20 mph when flooring it) and some loss of power when accelerating on the freeway. There is definitely hesitation and jerking when driving at some higher speeds and the car changes gear.

After some research im guessing it could be the fuel pump/sending unit or FRP sensor. I am trying to save money so any recommendations would be great on how to diagnose or what the issue might be.
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SN Certified Technician
Aug 14, 2009
Houston Texas
First thing. Stop. Put down the "parts changer" method to "fix" cars.

IF you really are interested in saving money then it will be necessary to spend a small amount of money on a tool that will pay for itself many times over by saving one from replacing good parts that don't fix the real problem. I hazard to guess it could have paid for itself already if used from the beginning. In addition it will help you to learn HOW to understand a modern car really works.

ForScan ODB2 scanner w ELM327 USB

Here's some information on where IMO every possible electrical problem should start.

Howto perform charging system voltage drop test

Once you have access to an ODB2 scanner that is capable of monitoring and/or graphing operational PID's, this will give access to the data needed to get a "toe hold" on the problem and start the trouble shooting process.

For example, IF you truly believe that it's a fuel rail pressures sensor problem (FRPS), then using the ODB2 scanner it's an easy process to cross check the fuel pressure with an external gauge. While you are at it, double check that the FRPS intake vacuum reference line is connected and leak free.

Also possible to cross check the FRPS with the long term fuel trims (LTFT) values.

In short, work on a theory. Use the ODB2 data to either prove it or rule it out.

Advice. Focus first an any misfire related DTC codes.

If you insist on looking for a part to change, then look for possible crank damper damage.