2004 Liberty 3.7L high fuel rail pressure

[04Liberty#!]

2004 Jeep Liberty 3.7L w/ 183675 miles
Codes P0132 and P0152 (high Voltages at upstream O2 sensors both sides) Lean
Fuel Rail Pressure is 60 to 65psi at 750rpm idle. Online info states fuel rail pressure should be 49 +or- 5psi
Dealer tells me needed parts are obsolete and I need to replace complete fuel tank with upper and lower fuel pump assemblies.
I have already recently replaced; cats, O2 sensors, coils, injectors, lower Fuel Pump Assembly (twice)
I believe the Fuel Pressure regulator is the issue. It is housed in the upper assembly.
After market suppliers have pressure regulator on smaller tube on lower assembly.
I have tried two but believe the regulators are not to 49 psi spec.
No sign of vacuum leaks. I did not remove regulator in stock upper fuel assembly when trying the new lower assemblies.
I am considering putting a pressure reducer inline before the fuel rail.
Thoughts?

 

[DadOSix]

X

 

[04Liberty#!]

Update:
Fuel Rail pressure at 750rpm idle is 65psi w/ needle bouncing +or- 3psi.
Engine running seems to be running smooth.
I pinched the flexible fuel line just upstream of the fuel rail as much as I dared.
RPM dropped to 650, pressure dropped to 62psi +or- 1psi, engine running smooth.
Thoughts?

 

[04Liberty#!]

Update:
I took out and reinstalled the old Fuel Pressure Regulator (FPR) in the upper assembly without the smaller O-ring.
To allow flow to the new FPR just below the upper assembly, leaving the large O-ring to prevent an always open return.
Primed the system a few times with the key and it started right up.
At first, idle smooth at 1200 to 1000 rpm with a Rail Pressure of 55. (Spec for the Spartan)
Confirming (to me) the old FPR in the upper chamber failed closed preventing flow to the new FPR just below the upper assembly.

At first when I revved the engine, it ran rough and miss fired. Sounded to me like air in the line.
A minute or two later, The idle rpm dropped back down to 650, keeping 55psi on the rail and running smooth.
But when I drove it, it stalled. After the first stall pumping the gas pedal keep it running enough to get back to the shop.
It felt to me like fuel pressure to the fuel rail was intermittent and/or with air. This triggered a number of new codes but not P0132 or P0152.

I; turned it off, cleared the codes, set up the fuel rail gauge so I could see it, started it up again.
It idled smooth, at 650rpm and rail pressure at 55 +or-1, when I revved it in between 650 and 3000 rpm.

Perhaps: the ECM is resetting things to the lower rail pressure.
And / or the old stock upper assembly without the lower o-ring on the FPR is allowing air in the fuel line.
Dealer and on-line sources tell me a new or old upper assembly is not available.

FYI: I had to change the wire connectors on the new lower assembly to connect to the original upper assembly.

Thoughts?

 

[DadOSix]

I am so confused by your process.

Are we looking at 2 separate issues?

 

[04Liberty#!]

As always there are probably many issues.
Your first response on my end was blank.
I am asking for information that may be helpful.

I believe:
The OEM FPR failed closed causing high rail pressure which eventually burnt-out CAT and Coil. The OEM FPR is no longer available.
The repair parts recommended by online sources (LFPA) are out of spec. High Pressure and wire connectors don't mate with OEM UFPA.
A new mating UFPA (now called a tank flange) is also not available.
Dealer tells me the whole fuel system including tank need to be replaced.

I'll send some pictures later today that may help clarify.

Thank you

 

[DadOSix]

As always there are probably many issues.
Your first response on my end was blank.
I am asking for information that may be helpful.

I believe:
The OEM FPR failed closed causing high rail pressure which eventually burnt-out CAT and Coil. The OEM FPR is no longer available.
The repair parts recommended by online sources (LFPA) are out of spec. High Pressure and wire connectors don't mate with OEM UFPA.
A new mating UFPA (now called a tank flange) is also not available.
Dealer tells me the whole fuel system including tank need to be replaced.

I'll send some pictures later today that may help clarify.

Thank you

True - I had a thought but my internet timed out.

I can't see why the fuel pressure would be responsible for cat and coil issues. A rich condition, maybe, but enough to burn those out? I dunno.

Initially, it seemed like you were chasing the downstream o2 sensors with respect to fuel pressure. IMO, and it is just that, my opinion, the 132 and 152 codes are pointing at electrical issues on the control side, not the feedback to the ecm. From what I read, the High voltage flag is setting because the sensor is seeing greated voltage across the sensor. There are 2 circuits - one that powers the sensor (and heater in the sensor) and the feedback loop to the ecm. So the 132 or 152 look like the sensor power is shorted to 12v somewhere. Note - it could be ANYWHERE as these jeeps are 20+ years old and did not use the best wiring. So, I would start at the sensor and chase backward - not just visually, but actually pulling, moving, jiggling anything in the wire path.

I know you state now that the codes are gone, so i dunno where things changed.

A few pics would definitely not hurt.

 

[Intermechanico]

Fuel trim (time injector is open) is directly related to fuel supply pressure. If the pressure is higher than normal, more fuel will be injected over a given period of time.

The ECM adjusts fuel trim to accomodate component wear, but only to a point, and it is not instantaneous.

If your fuel supply pressure is siting at 60-65 psi, or 10-15 psi above the 49 psi specified pressure, the system will overfuel up to 20-30%.

The ECM will adjust short and long term fuel trim to accommodate the condition, but this will not happen until the ECM achieves Closed Loop, engine warm. Until then, the ECM will employ the factory open loop fuel curve, which is generally rich by default. With fuel supply pressure operating at 20-30% higher than normal, the Open Loop fuel curve will be very rich. Depending on time to achieve Closed Loop, the cats could just warm up more quickly or sustain damage from overheating.

Next Steps:

1. Correct the fuel pressure fault, verify operating pressure is maintained at the specification you provide at idle, as well as under load (Torque Stall)

2. Do you have a scan tool capable of displaying real time engine data, specifically Long and Short term fuel trim? If so, reset the Long and Short term trim to establish a new baseline for the ECM to work from.

 

[DadOSix]

Fuel trim (time injector is open) is directly related to fuel supply pressure. If the pressure is higher than normal, more fuel will be injected over a given period of time.

The ECM adjusts fuel trim to accomodate component wear, but only to a point, and it is not instantaneous.

If your fuel supply pressure is siting at 60-65 psi, or 10-15 psi above the 49 psi specified pressure, the system will overfuel up to 20-30%.

The ECM will adjust short and long term fuel trim to accommodate the condition, but this will not happen until the ECM achieves Closed Loop, engine warm. Until then, the ECM will employ the factory open loop fuel curse, which is generally rich by default.

Thanks!

I understand that loop better now.

 

[Intermechanico]

2004 Jeep Liberty 3.7L w/ 183675 miles
Codes P0132 and P0152 (high Voltages at upstream O2 sensors both sides) Lean
Fuel Rail Pressure is 60 to 65psi at 750rpm idle. Online info states fuel rail pressure should be 49 +or- 5psi
Dealer tells me needed parts are obsolete and I need to replace complete fuel tank with upper and lower fuel pump assemblies.
I have already recently replaced; cats, O2 sensors, coils, injectors, lower Fuel Pump Assembly (twice)
I believe the Fuel Pressure regulator is the issue. It is housed in the upper assembly.
After market suppliers have pressure regulator on smaller tube on lower assembly.
I have tried two but believe the regulators are not to 49 psi spec.
No sign of vacuum leaks. I did not remove regulator in stock upper fuel assembly when trying the new lower assemblies.
I am considering putting a pressure reducer inline before the fuel rail.
Thoughts?

“2004 Jeep Liberty 3.7L w/ 183675 miles
Codes P0132 and P0152 (high Voltages at upstream O2 sensors both sides) Lean”

O2 Sensor Signal - High Voltage - generally means rich condition, not lean. O2 Sensor signal voltage operates as:

Lean Mixture - Lower than .5 volts
Rich Mixture - Higher than .5 volts
Stoichiometric - .5 volts

During normal conditions, Upstream O2 signal voltage will fluctuate constantly above and below .5 volts as the ECM adjusts fuel trim in real time, never remaining on either side of .5 volts for long

SUPPLEMENTAL: Google Gemini

P0132 / P0152 Thresholds: In the Chrysler JTEC/NGC engine controller, these codes don't trigger simply for being above 0.5V (a normal rich swing is 0.6V–0.9V). They set when the signal voltage gets pinned unusually high (typically above 0.99V to 1.1V+) for a calibrated window (usually 30–60+ seconds). Pointing out that the sensors are "pegged high" reinforces why the PCM flagged a circuit high/short code rather than just a routine rich mixture code like P0172/P0175.

 

[Intermechanico]

Also, there is a possibility that your fuel pressure is within spec at 60 psi. 2002-2003 spec is 49psi, while the spec changed in 2004 to 58 +/- 5 psi

 

[DadOSix]

“2004 Jeep Liberty 3.7L w/ 183675 miles
Codes P0132 and P0152 (high Voltages at upstream O2 sensors both sides) Lean”

O2 Sensor Signal - High Voltage - generally means rich condition, not lean. O2 Sensor signal voltage operates as:

Lean Mixture - Lower than .5 volts
Rich Mixture - Higher than .5 volts
Stoichiometric - .5 volts

During normal conditions, Upstream O2 signal voltage will fluctuate constantly above and below .5 volts as the ECM adjusts fuel trim in real time, never remaining on either side of .5 volts for long

SUPPLEMENTAL: Google Gemini

P0132 / P0152 Thresholds: In the Chrysler JTEC/NGC engine controller, these codes don't trigger simply for being above 0.5V (a normal rich swing is 0.6V–0.9V). They set when the signal voltage gets pinned unusually high (typically above 0.99V to 1.1V+) for a calibrated window (usually 30–60+ seconds). Pointing out that the sensors are "pegged high" reinforces why the PCM flagged a circuit high/short code rather than just a routine rich mixture code like P0172/P0175.

Execllent stuff! School appears to be in session!

 

[04Liberty#!]

Thanks for the input.
Attached are photos that may help
It most likely ran hot and with these and other codes for a long time. CAT and coil were definitely burn plugs and injectors filthy.
And when it would not pass emissions, it became my issue. It has been abused for sure.

I have focused on correcting rail pressure after cats, plugs, coils and injectors because all other codes went away after. And I read high rail pressure can cause the system to constantly self-correct causing the P0132 and P0152 codes. And it is easy to verify rail pressure. I figured get rid of these codes and see what happens next.

I do not have a real time scan tool but can probably get my hands on one.
To get the 49psi, I need a part, I cannot find. (see attachment). This is early 2004 so maybe 49psi is correct. If spec is higher why the codes?
Rail Pressure did come down when I did as explained in the attachment.

I will get my hand on a real time scanner and consider all Then let you know what I do and find.
If you have additional thoughts after looking at the attachment, please let me know.

Thanks for the help.
I want to get this little jeep in the mountains for some hunting.

 

[04Liberty#!]

Update:
Jeep was stalling when I gave it gas so I extended Fuel Gauge hose so I could see it from the driver's seat. It felt like low fuel pressure or air in the line. I suspect it may be due to the OEM FPR O-ring I removed. (as noted in previous attachment, Removing the O-ring allowed the new online PRV to work) But it has not stalled since i moved the gauge. OEM FPR is still in OEM UFPA without bottom O-ring and spring. Rail Pressure is holding steady at 55 over 600-4000 RPM range.

I have located a few same year & models at YPI close buy and will try to salvage some FPR & UFPA with 49psi setting. Otherwise, no luck on finding 49psi FPR or UFPA parts.

I checked new DriveBolt O2 sensors are in correct location by lead length. Short lead upstream. Long lead downstream? Only difference I could see. New Replacement 2292-03687545 Plugs/coil kit and TRQ injectors should be ok? New CATs might be sketchy but would be downstream O2 issue?

I barrowed my sons code reader. Attached is real time readings at idle. Looks like the PCM is pretty confused. It now running rough with a little light backfire. I need get more readings and graph overtime. B1&2 S1's are pegged could be fuel rail pressure or wire fault. Even with codes it ran better at 60psi rail pressure when OEM PRV o-ring and spring in place. As suggested, I think it best to get fuel rail pressure closer to 49psi before running it a bunch.

Thoughts?

 

[Intermechanico]

Do you recall the O2 sensor part numbers? We should verify they are correct and verify their rated output voltage. Apparently, Chrysler PCMs are very sensitive to O2 sensor signal voltage.

Noted:
The upstream O2 sensor (item 16 and 20) voltages are out of range high, as far as I know 1.27v is not a voltage that the sensor can generate on its own.

Let’s park the fuel pressure issue for now, it’s not likely to be the core problem.

We need to find out what the actual output voltage is from the upstream O2 Sensors at the PCM, which is located on the drivers side inner fender.

I’m not 100% certain the PCM pin Locations are accurate, but this is what I found:


************
Look for the second plug down from the top of the PCM with the orange insert to backprobe Pin 31 (Bank 1), Pin 33 (Bank 2), and Pin 32 (Shared Sensor Return/Ground).



Bank 1, Sensor 1 (Driver Side Upstream):

Signal: Pin 31 (Circuit ⁠K41⁠, Dark Blue / Light Blue trace)

Sensor Return / Ground: Pin 32 (Circuit ⁠K902⁠ / ⁠K904⁠, Dark Blue / Dark Green trace)


Bank 2, Sensor 1 (Passenger Side Upstream):

Signal: Pin 33 (Circuit ⁠K43⁠, Dark Blue / Light Green trace, or Dark Blue / Pink)

Sensor Return / Ground: Pin 32 (Shares the common upstream/downstream sensor return circuit at Pin 32)


Testing Guidance


Common Return/Ground Point: Because both upstream sensors return(are grounded) to Pin 32, an open or high-resistance fault on that single return circuit will float both inputs simultaneously, pinning both B1S1 and B2S1 directly to 1.27V on the scan tool. In my mind, a return circuit fault is the most likely culprit as it is the factor that links to two sensors, while the signal circuits are separate both at the sensors and within the PCM.


Probing Procedure:
-Key ON, Engine Running
-Use Volts DC setting, set range to lowest setting that is above 2 volts DV

Backprobing: use a thin metal pin such as a safety pin or similar to push/slide between the wire and the connector socket, do not pierce the wires insulation (that guy eats alone at lunchtime lol). The goal is to contact the terminal without damaging the wire or disconnecting the connector.

We should check the integrity of pin 32 (Signal Return) first. Put the multimeter black lead on the negative battery terminal and probe Pin 32 with the red lead (Key ON). It must read less than 0.05V (50 mV). If Pin 32 measures higher than that, the sensor return circuit is open or resistive.

Backprobe (positive multimeter probe) Pin 31. Backprobe (Negative multimeter probe) Pin 32 for Bank 1 upstream O2 signal voltage.

Perform the same for Pin 33 (positive) to Pin 32 (negative) for Bank 2.

A normal upstream O2 signal reading will be in the higher portion of .1-.9 vdc while the engine warms up, changing to a voltage reading that switches constantly above and below .5 vdc once the engine is warmed up at the PCM is in Closed Loop Mode.


If the meter measures higher than .9 vdc, turn the key off and disconnect the connector to inspect for corrosion or damage. It suggests that there is an issue with the sensor return (ground) circuit that is pushing the signal voltage high.

If the meter measures 0.1V–0.9V between the pins while the scan tool still displays 1.27V, there may be an issue with the PCM. In my world of off highway equipment, the ECM is not usually at fault.

 

[04Liberty#!]

Thank You
Will do and report what I find.

 

[04Liberty#!]

O2 Sensors:
Upstream, Drive Bolt, SKU: ST-24253 short lead
Downstream, Drive Bolt, SKU: ST-24460, Long lead
Other than the leads they looked identical.
Purchased from Parts Geek
no model or part number given just the SKU.
No literature in the box. No; part Number, SKU or model on the boxes

 

[04Liberty#!]

InterMechanico
Can you direct me to a reliable PCM Pin Number schematic.
I have found several online that do not agree with each other or your description or what i'm seeing.
(see Attached)
PCM;Part #, Serial #, Sequence #, bar code and other Identifiers are shown.
There are 4 plugs. I labeled them A, B C D rear to front. A being the rear plug.
Each plug has 38 pins (or pin locations) numbered as shown.

Much appreciated.

 

[Intermechanico]

No problem.

It looks like you have connector C4 disconnected. Plug that guy back in .


PCM Identification & Connector Layout
Module Type: Motorola NGC3 controller.


Connector Order (Top to Bottom):


The connector identifier letters stamped/printed along the edge: A, B, C, D corresponding directly to C1, C2, C3, C4:


C1 (A - Top): Black — Main power feeds, ground bus, and data communications.


C2 (B - Second down): Orange — Engine Sensors & O2 Harness (This is the target connector).


C3 (C - Third down): White / Natural — Injectors, coils, and secondary engine management.


C4 (D - Bottom): Green (shown disconnected in the lower inset photo) — Electronic Transmission Control (42RLE).


Pin Cavity Verification (38-Way Connector)


The pin grid at the bottom of your image gives the exact terminal map looking into the connect or


Row 1 (Top): Pins 1 through 10


Row 2: Pins 11 through 19


Row 3: Pins 20 through 28


Row 4 (Bottom): Pins 29 through 38


On Connector C2 (Orange Index / Port B):


Pin 31: Bank 1, Sensor 1 (Driver Upstream Signal — Dark Blue / Light Blue trace). This is in the bottom row, 3rd terminal in from the left.


Pin 32: Shared Sensor Return / Signal Ground (Dark Blue / Dark Green trace). This is in the bottom row, 4th terminal in from the left.


Pin 33: Bank 2, Sensor 1 (Passenger Upstream Signal — Dark Blue / Light Green or Pink trace). This is in the bottom row, 5th terminal in from the left.

 

[04Liberty#!]

Thanks! Intermechanico, great instructions.

Plug 4 is in.
My last attachment was not clear. Please reference new one.

At Idle Tests:
Black probe to - Battery post, Red Probe to pin 32, Results: .5 t0 4.6 mV
Black Probe to Pin 32, Red Probe to pin 31, Results: 25 to 102 mV
Black Probe to Pin 32, Red Probe to pin 33, Results: 25 to 150 mV

Thoughts?

I'm going to try and salvage 4psi FPR tomorrow. I'll Report back.