Long term fuel trim out of wack.

[airline tech]

What was the exact O2 Heater code initially and which sensor has been replaced and which wire harness was replaced?
To confirm all the other items being replaced is to address the high LTFT issue- Correct
Is the LTFT high at both Idle and above Idle? This is a very important piece of information on the data.
Ask the dealer to give you a printout of the PID data that they are seeing and I can possibly look it over and note something they may be missing or appears out of normal and not coding.
I had a strong hunch the Injectors would be a no help issue.

As of now the one thing that provided a change is the wire harness replacement, so was the LTFT high before it was replaced?

My next direction would be to focus on the full O2 sensor circuit and the associated VREF as it’s a shared circuit and a slightly skewed O2 sensor from that circuit may be the root of the issue, again I am just thinking of things that would be causing the issue and since I do not know exactly what they are seeing and have they checked the wiring circuit, I am flying blind here.

Sponsored

 

[Starjammir]

They replaced the pre cat 02 sensor.
Complete engine harness was replaced.
I don't have access to their scans however I know the service manager well and csn relay it all over to her.

 

[Starjammir]

And no, all things were NOT replaced due to the fuel trim. Was originally for a heater circuit O2 sensor code. They found a leak at the bung for the O2 sensor so they replaced the cat. Didnt fix the O2 sensor light. Replaced a vacuum pump, engine harness finally solved the issue. Along this whole time fuel trims have been a mess, super high going to super low.
Now, they seem to have stabilized less than 20 but are still to high. Now they are chasing the high fuel trim. Again NO CEL on for it. Just monitoring it and seeing it's high

 

[Starjammir]

I'll talk to Kayla tomorrow and get a print out of the LTFT and what they see. Ill ask about them at idle and above? Idle.
What RPM would you like? Also I'm assuming you want the truck warmed up?

 

[RangerBill]

And no, all things were NOT replaced due to the fuel trim. Was originally for a heater circuit O2 sensor code. They found a leak at the bung for the O2 sensor so they replaced the cat. Didnt fix the O2 sensor light. Replaced a vacuum pump, engine harness finally solved the issue. Along this whole time fuel trims have been a mess, super high going to super low.
Now, they seem to have stabilized less than 20 but are still to high. Now they are chasing the high fuel trim. Again NO CEL on for it. Just monitoring it and seeing it's high

What do they mean by vacuum pump? I never heard of one on the Ranger.

 

[Starjammir]

I haven't either. It's what I was told by them.
Not that I'm complaining as they have given me 5 new cars to drive so far. If you want to know anything about any of the Ford fleet minus the mustang let me know!

 

[RangerBill]

I haven't either. It's what I was told by them.
Not that I'm complaining as they have given me 5 new cars to drive so far. If you want to know anything about any of the Ford fleet minus the mustang let me know!

I found a vacuum pump mentioned in the shop manual for the brake system, to boost vacuum to the master cylinder booster.

In the ABS description of braking operation, it states that if the master cylinder vacuum booster vacuum is low, the HCU (hydraulic control unit) in the ABS module responds by boosting hydraulic pressure via an electric pump built into the ABS module. I still don't see any info on a vacuum pump, only a mention of it being used on some vehicles.

 

[airline tech]

From my post above
"and Vacuum Pump???? I assume you are referring to the brake booster hose (aspirator valve)"

This is what I am referring - this takes the place of the vacuum pump, since our Ranger does not have the physical vacuum pump.

When the booster vacuum drops (This is the sensor on the bottom of the brake booster (Vacuum Pressure Sensor) it signals this valve to open, suppling an extra secondary vacuum source from the air induction tubing

I suspect they replaced this chasing a possible vacuum leak source.


Here is the manual description of it:


Vacuum On Demand System

Vehicles equipped with a 2.3L engine supply vacuum to the brake booster through the use of a valve solenoid and an aspirator in the brake booster vacuum tube. When the ABS module detects a low vacuum condition in the brake booster, a message is sent to the PCM requesting additional vacuum. The PCM responds by opening the valve solenoid which allows the engine to draw air from the brake booster, increasing vacuum in the booster. Once the vacuum in the booster has reached the required level, the ABS module stops sending the message and the PCM closes the valve solenoid.

If fuel trims are all over the place and (not consistent) then it would be sensor related.
I would start with everything on the VREF circuit for the MAP Sensor

VREF Shared:

MAP Sensor
Fuel Rail Pressure Sensor
Eng Oil Pressure Sensor
DPFE Sensor

Signal Return Shared: (Shared 1)

MAP Sensor
Fuel Rail Pressure
Eng Oil Pressure Sensor
Wastegate Motor


Signal Return Shared: (Shared 2)
(Note: The shared VREF feeds the DPFE, but the DPFE has a separate signal return) from the above sensors.

DPFE - Diff Press Feedback
ECT - Eng Coolant Temp
CHT - Cylinder Head Temp
EGRT (EGR Temp Sensor)
Exhaust Press Sensor

And the VREF Feed for the (Wastegate Motor) is also a shared VREF

Wastegate Motor
EGR Valve

My hunch is one of the listed sensors is slightly biased with high possibility of the MAP (VREF) circuit or its primary signal return.
The secondary signal returns and VREF are only a slight possible.

I am shocked that they were willing to pull the head and replace (Intake Valves) but skipped over the (main sensor) that has control for airflow calculations which also drives fuel trim tables.

So, for me the issue is most likely with the MAP sensor or its associated circuit.

Biased Map Sensor

PCM (Thinks) Low Airflow - Commands Less Fuel - O2 Sensor sees more air than fuel and the PCM adds fuel (High LTFTs)


Biased Fuel Rail Pressure Sensor:

PCM thinks pressure is OK, Injectors actually under deliver fuel - O2 Sensor sees more air than fuel and the LTFT's rise as the PCM adds more fuel

So, this is my preliminary take on what is happening, it would need a true monitor of the PID data to confirm it - but my high suspects are on this circuit, or one of these 2 sensors is not reading true pressure.

Yes, there are many other factors to consider, I just have not heard any mention that these were checked and confirmed good and should be checked before throwing any more parts at it.

 

[Dr_Strangelove]

I haven't either. It's what I was told by them.
Not that I'm complaining as they have given me 5 new cars to drive so far. If you want to know anything about any of the Ford fleet minus the mustang let me know!

You should start complaining and maybe you'll get to test the new Mustang, yet.

(Just being funny.)

 

[diesel924]

If you look in the service manual under 'Reference Values', the normal LTFT is a whopping -20 to +20%. STFT are -10 to +10%. What is the symptom they are trying to fix? Is it poor mileage? If the truck is NOT throwing a check engine light, what is the chief complaint?

 

[airline tech]

Yes the manuals provide a broad range but this is PCM control range.
Normal STFT = near 0 % & LTFT should be about 7 to 8 % , now there is always some variance.
Ideally you want the LTFT to average within the 10% window from zero

Sponsored