Codes P0172 and P0175, stumbles in park and at high RPM's

Hi,

If the vehicle is running rich, the first thing I would check is fuel pressure. If it is too high due to a faulty fuel pressure regulator, it can cause this.

Let's start there. Here is a link that explains how to test fuel pressure:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Here are the directions specific to your vehicle. The attached pics correlate with these directions. Also, the manufacturer's specs are included in the directions.

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2005 Jeep Truck Liberty 4WD V6-3.7L VIN K
Fuel Pump Pressure Test
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Pump Fuel Pressure Testing and Inspection Component Tests and General Diagnostics Fuel Pump Pressure Test
FUEL PUMP PRESSURE TEST
Use this test in conjunction with the Fuel Pump Capacity Test, Fuel Pressure Leak Down Test and Fuel Pump Amperage Test found elsewhere in this group.

Check Valve Operation: The bottom section of the fuel pump module contains a one-way check valve to prevent fuel flow back into the tank and to maintain fuel supply line pressure (engine warm) when pump is not operational. It is also used to keep the fuel supply line full of gasoline when pump is not operational. After the vehicle has cooled down, fuel pressure may drop to 0 psi (cold fluid contracts), but liquid gasoline will remain in fuel supply line between the check valve and fuel injectors. Fuel pressure that has dropped to 0 psi on a cooled down vehicle (engine OFF) is a normal condition.

When the electric fuel pump is activated, fuel pressure should immediately (1-2 seconds) rise to specification.

The fuel system is equipped with a separate fuel pump module mounted, fuel pressure regulator. The fuel filter is remotely mounted. The fuel pressure regulator is not controlled by engine vacuum.

Warning: the fuel system is under constant fuel pressure even with the engine off. Before disconnecting fuel line at fuel rail, this pressure must be released. Refer to the fuel system pressure release procedure.

Fig.20 Fuel Pressure Test Gauge (Typical Gauge Installation At Test Port)

pic 1

1. Remove protective cap at fuel rail test port. Connect the 0 - 414 kPa (0 - 60 psi) fuel pressure gauge (from gauge set 5069) to test port pressure fitting on fuel rail. The DRB III Scan Tool along with the PEP module, the 500 psi pressure transducer, and the transducer-to-test port adapter may also be used in place of the fuel pressure gauge.
2. Start and warm engine and note pressure gauge reading. Fuel pressure should be 339 + 34 kPa (49.2 + 5 psi) at idle.
3. If engine runs, but pressure is below 44.2 psi, check for a kinked fuel supply line somewhere between fuel rail and fuel pump module. If line is not kinked, but specifications for either the Fuel Pump Capacity, Fuel Pump Amperage or Fuel Pressure Leak Down Tests were not met, replace lower section of fuel pump module. Refer to Fuel Pump Module Removal/Installation.
4. If operating pressure is above 54.2 psi, electric fuel pump is okay, but fuel pressure regulator is defective. Replace lower section of fuel pump module. Refer to Fuel Pump Module Removal/Installation.
5. Install protective cap to fuel rail test port.

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Let me know the results. I can tell you that if the pressure is too high, the regulator is located on top of the fuel pump module (top of fuel tank) and is not serviceable. It will need to be replaced.

Let me know what you find or if you have other questions.

Take care,
Joe

Hi,

I just read through the diagnostics. It indicates that if the pressure is above 54.2 (operating pressure) the pump is good, but the regulator is bad. Again, based on the specs, if you have 59 PSI, it's too high and is the likely cause of the rich fuel mixture.

Do me a favor. Take a look at number 4 in the diagnostics I sent. Are you above that pressure?

Let me know.

Joe

Hi,

You are very welcome. Hang in there, we'll figure it out. As far as the specs, that is what is listed for this vehicle and engine. If you have a chance, let me know what you find.

Joe

Hi,

I will be out for surgery for a couple of days. I just wanted to let you know. However, I will be back as soon as possible. If you need help, please feel free to reply to this link at any time. The site owner will be covering for me.

Take care and I'll keep my fingers crossed that this takes care of the issue.

Joe

Hi,

It could be an injector issue, but before replacing it, I would suggest switching the injector from the misfiring cylinder to a non-misfiring cylinder and see if the misfiring cylinder changes. Here are the directions for removal and replacement. The attached pic correlates with the directions
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2005 Jeep Truck Liberty 2WD V6-3.7L VIN K
Fuel Injector Removal and Installation
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Injector Service and Repair Procedures Fuel Injector Removal and Installation
FUEL INJECTOR REMOVAL AND INSTALLATION
REMOVAL
1. Remove fuel rail.

Injector Retaining Clip

pic 1

2. Disconnect clip(s) that retain fuel injector(s) to fuel rail.

INSTALLATION
1. Install fuel injector(s) into fuel rail assembly and install retaining clip(s).
2. If same injector(s) is being reinstalled, install new O-ring(s). Two different O-rings are being used. These can be easily identified by color. Install black O-ring at intake manifold end of injector. Install red/rust colored O-ring at fuel rail end of injector.
3. Apply a small amount of clean engine oil to each injector O-ring. This will aid in installation.
4. Install fuel rail.
5. Start engine and check for fuel leaks.

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Please note that the diagnostics indicate a regut0r issue; Too much pressure. Make sure to check the fuel pressure again to see if it is above the specs. I don't want you to purchase more parts to find it doesn't fix the problem.

Let me know what you find.

Take care. PS: I'm writing this from the hospital. If there is a delay in getting back to you, I apologize in advance.

Take care,

Joe

As far as normal, it's on the higher end, but it still is in what is considered the normal range. I am home now and hardly remember anything from the hospital. However, I believe there was a high fuel pressure issue. Have you checked that?

Joe

Hi,

The fuel pressure is 57? If so, it's higher than max of 54 PSI and both codes are indicating a rich fuel mixture. Was the regulator replaced when you did the fuel pump?

Sorry about that. The fuel pump module is all part of it. (Filter, pump, regulator and so on). Too many vehicles in my mind.

Listen, since the codes are set and pressure is really close to being in spec, we need to check the O2 sensors. We could have a short there.

Here is what I need you to do:

Start the engine.
Allow the engine to reach normal operating temperature.

NOTE:
- If one of the O2 Sensors Signal or Return circuit is shorted to ground or voltage, all the other O2 Sensor voltage readings will be affected.
- verify proper O2 Sensor operation. If all the O2 Sensor voltage readings have not returned to normal, follow the diagnostic procedure for the remaining O2 Sensors.

With the scan tool, monitor the 2/1 O2 Sensor voltage reading.

Voltage should be switching between 2.5 and 3.4 volts?

Let me know. Also, let me know what the engine coolant temperature sensor is indicating in relation to the ambient temperature. The sensor could be causing a rich mixture as well.

Joe

I think you have bad sensors. They should be between 2.5 and 3.4. If they are going radical as you described, they sound faulty.

Joe