P0171/P0174: The codes of frustration!

[rgorke]

My CEL light comes on again restarting car after driving spawn to school and stopping at supermarket. Below are the freeze frame status from both codes. Other than the LTFT being at 25%, any other numbers out of whack? What is confusing and frustrating is that after the codes are thrown, I drive home monitoring the STFT and LTFT and get steady values of +/- 3% for STFT and 10-15% LTFT while driving at 1500 and 2500 rpm AND at idle in the driveway. My smoke tests haven't revealed any leaks that I can see.

Also, what "should" LTFT levels be? STFT: +/- 3%?

Thoughts?

Repair list
-New vacuum harness to manifold tube/brake booster/intake snorkel.
-New crankcase vent tube
-New fuel filter
-5-6 or more tanks of Lucas injector cleaner

Freeze Frame Data
P0171
System Too Lean (Bank 1)

Status of this DTC
Confirmed DTC

Engine state when the fault appeared
Freeze frame trouble code: P0174
Fuel system status 1: Closed loop (using all oxygen sensor)
Fuel system status 2: Unused
Calculated load value: 20.8 %
Coolant temperature: 199 °F
Short term fuel % trim Bank 1: 9.4 %
Long term fuel % trim Bank 1: 25.0 %
Short term fuel % trim Bank 2: 12.5 %
Long term fuel % trim Bank 2: 25.0 %
Intake Manifold Pressure: 15.7 inHg
Engine RPM: 706.25 rpm
Vehicle speed: 1 mph
Timing advance: 13.0 °
Intake air temperature: 57 °F
Maf air flow: 0.68 lb/min
Absolute Throttle sensor position: 12.2 %
Oxygen sensor voltage bank1 sensor1: 0.110 Volt
Short term fuel associated to bank1 sensor1: 9.4 %
Oxygen sensor voltage bank1 sensor2: 0.795 Volt
Short term fuel associated to bank1 sensor2: 99.2 %
Oxygen sensor voltage bank2 sensor1: 0.155 Volt
Short term fuel associated to bank2 sensor1: 12.5 %
Oxygen sensor voltage bank2 sensor2: 0.835 Volt
Short term fuel associated to bank2 sensor2: 99.2 %
Fuel rail pressure relative manifold: 55.296 psi
Relative throttle position: 0.0 %
Commanded throttle actuator control: 0.4 %

P0174
System Too Lean (Bank 2)

Status of this DTC
Confirmed DTC

Engine state when the fault appeared
Freeze frame trouble code: P0174
Fuel system status 1: Closed loop (using all oxygen sensor)
Fuel system status 2: Unused
Calculated load value: 20.8 %
Coolant temperature: 199 °F
Short term fuel % trim Bank 1: 9.4 %
Long term fuel % trim Bank 1: 25.0 %
Short term fuel % trim Bank 2: 12.5 %
Long term fuel % trim Bank 2: 25.0 %
Intake Manifold Pressure: 15.7 inHg
Engine RPM: 706.25 rpm
Vehicle speed: 1 mph
Timing advance: 13.0 °
Intake air temperature: 57 °F
Maf air flow: 0.68 lb/min
Absolute Throttle sensor position: 12.2 %
Oxygen sensor voltage bank1 sensor1: 0.110 Volt
Short term fuel associated to bank1 sensor1: 9.4 %
Oxygen sensor voltage bank1 sensor2: 0.795 Volt
Short term fuel associated to bank1 sensor2: 99.2 %
Oxygen sensor voltage bank2 sensor1: 0.155 Volt
Short term fuel associated to bank2 sensor1: 12.5 %
Oxygen sensor voltage bank2 sensor2: 0.835 Volt
Short term fuel associated to bank2 sensor2: 99.2 %
Fuel rail pressure relative manifold: 55.296 psi
Relative throttle position: 0.0 %
Commanded throttle actuator control: 0.4 %

 

[rgorke]

A small update: I went through a systems check of all the sensors and the O-32 EGR Monitor Bank 2: 82 - Manufacturer Specific:
Value: 0.122 (in red, meaning out of range)
Min: -4.753
Max: -4.737
Units: psi

So, does this mean my EGR monitor is not working or is there something else going on? Could there be a leak to the EGR?

 

[joegr]

I don't remember what, but there is something on both of mine that my scan tool claims is out of range, but it has made this claim for years (from the first time I scanned either). I have no issues or warning lights.

That said, I have had one EGR assembly failure, and I have heard of a few others. Also, the vacuum hard lines running to the EGR assembly and the fuel pressure sensor will crack if you just look at them wrong. The break may not be visually obvious.

 

[rgorke]

I don't remember what, but there is something on both of mine that my scan tool claims is out of range, but it has made this claim for years (from the first time I scanned either). I have no issues or warning lights.

That said, I have had one EGR assembly failure, and I have heard of a few others. Also, the vacuum hard lines running to the EGR assembly and the fuel pressure sensor will crack if you just look at them wrong. The break may not be visually obvious.

Thanks and I did notice those vacuum lines between the throttle body, EGR and fuel pressure sensor that are tiny. They do appear very flimsy.

Finally, the CEL is off, again. I've been monitoring the STFT and LTFT and they are all well below 25%. It seems as though at certain times the LTFT spikes up for a minute or two and then the code gets thrown. The majority of the time it is well within appropriate limits. This is driving me nuts...what is causing the spikes???? Argh!!!!

 

[rgorke]

Joe, I replaced the EGR vacuum lines. My existing lines were hard, partially melted and starting to crack. The new one I put on is much much better. Now it appears that my fuel trims seem to be behaving. But we shall see. I still have that EGR monitor sensor value that is low.