Misfire Detected with Low Fuel
This code indicates that the PCM has detected an engine misfire accompanied by a low fuel condition.
Code Set Parameters
The PCM uses crankshaft position, camshaft position, and engine RPM to calculate fuel delivery and ignition timing. Variations in camshaft and crankshaft position, as well as engine RPM help the PCM to detect an engine misfire. When an engine misfire is detected that is severe enough to damage the catalytic converter/s, a code will be stored in the PCM and a service engine soon lamp will be illuminated. If the misfire is not considered serious enough to damage the catalytic converter/s, the service engine soon lamp may flash for a period of time (usually under acceleration) and then go off.
Symptoms may include a rough running engine, hesitation upon acceleration, delayed engine starting, a no-start condition, and an overall lack of engine power.
The most likely cause of code P0313 is an engine misfire caused by a lean fuel mixture. This can be caused by a clogged fuel filter, bad fuel pump, clogged or faulty fuel injectors, shorted or open electrical circuits in the fuel pump or fuel injection system, unplugged or corroded electrical connectors. Other possibilities may include bad spark plugs, bag ignition coils, bad spark plug wires, a bad distributor cap or rotor button, low compression, or a large vacuum leak.
Ignition system components are often replaced in error when this code is exhibited. While they are the most likely culprits, other factors can also play into the misfire equation.
- A scanner (or code reader) and a digital volt/ohmmeter will be helpful in successfully diagnosing this code-storing condition.
Begin your diagnosis with a visual inspection of all wiring and connectors
- Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
- Always retest the system after repairs are completed to ensure success.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
- This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
- After the codes are cleared, operate the vehicle to see if the code returns
- If the code fails to immediately return, you may have an intermittent condition
- Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made.
A cylinder misfire code is easiest to diagnose when obvious symptoms are presented
- If a code is stored and no symptoms are manifest, then reset the PCM and see if the code returns
- Is the engine stumbling or hesitating upon acceleration? If so, then make sure that all ignition maintenance tune-up items have been replaced according to the manufacturer’s recommended schedule
- This includes the spark plugs, spark plug boots (where applicable), ignition coils (or coil packs), distributor cap and rotor button (if equipped), and the fuel filter
- It is best to replace the spark plugs using OEM replacement parts
- Resistor spark plugs are cheaper than platinum spark plugs but they are not a viable substitute
- Since the code has pointed to a specific cylinder, diagnosis has been made somewhat easier
- You may move coils, spark plugs, and spark plug wires and boots from one cylinder to another
- By doing this you can see if the system malfunction trades cylinders with the ignition system components and replace parts as necessary
- If no shortcomings are found with the ignition system, then check for a lean exhaust condition by observing the oxygen sensor data
- Should the data suggests a lean exhaust condition, you would be looking for a major vacuum leak caused by a cracked, broken, or disconnected vacuum hose, an exhaust gas recirculation (EGR) valve malfunction, inoperable fuel injectors, compression problems, or clogged catalytic converter/s
- Unmetered air that enters the engine without entering the MAF may also cause this code to be stored
- A scanner and access to a factory service manual is critical to a successful diagnosis.
If no ignition misfires are found, suspect a misfire caused by a lean fuel mixture
- If other diagnostic codes are present, diagnose and repair them before attempting to diagnose the P0313
- These codes may include a fuel volume regulator code, a cylinder specific misfire code, a MAF code, or an injector circuit code
- To successfully diagnose a low fuel (or lean fuel mixture) condition, you will need a few special tools; a fuel pressure tester (with adapters), a digital volt/ohmmeter, a set of “noid” lights, and a scanner
- Begin by making sure that the fuel tank is at least half-full of fuel
- Connect the fuel pressure tester to the service valve (if equipped)
- It is usually located on the fuel injector rail
- After the fuel pressure tester is connected, open the pressure release valve and allow the fuel pressure to drain into a suitable container
- A large clear glass jar works well because you can observe contaminants in the fuel after it settles in the jar
- Close the valve and secure the tester away from moving engine parts so that it will not be damaged
- Turn the key to the on position
- The fuel pump should engage (it should make a slight humming noise when activated) and then turn off
- This is how the fuel pump is primed prior to engine startup
- Check the pressure reading on the tester
- If no pressure is observed, then attempt to start the engine
- Check the pressure reading again
- Compare the reading to manufacturer’s specifications
- If fuel pressure is low (or non-existent) and no humming was heard from the fuel pump, suspect a fuel pump problem
- A great method for testing the fuel pump is to gently tap the bottom of the fuel tank with a large rubber mallet while the engine is being cranked
- If the fuel pump begins to operate with contact, then you know for sure that you have a faulty fuel pump
- If a hum was heard from the fuel pump and no fuel pressure is indicated, then begin testing by disconnecting the fuel lines from the fuel filter and draining the filters contents
- If the filter contains debris or the contents appear black and dirty, suspect a clogged fuel filter
- If the contents of the filter do not appear dirty, reconnect the lines and check for leaks
- Unplug the electrical connector from the fuel pump (on top of the fuel tank) and check for system voltage
- See the manufacturer’s specifications but the fuel pump usually operates on battery voltage (present during the initial priming process, when the engine is being cranked, or the engine is running)
- Do not forget to check the system ground signal, as well
- If system voltage checks out and the fuel pump fails to operate, drop the fuel tank and replace the pump (don’t forget to replace the sock and the filter).
If the fuel pump operates and fuel pressure is present, test injector operation by listening to an injector using a stethoscope or other suitable listening device
- Each injector should make a ticking sound as it operates and sprays fuel into the cylinder or throttle body
- If no ticking is heard, check for voltage and ground pulse at the injector connector/s using a “noid” light
- If there is no voltage present, check fuses and relays
- If no ground pulse is present, test the fuel injector relay, the PCM relay, and the PCM for a short or open circuit
- Repair as necessary.