A couple of questions re P0171/P0174 codes

[goony]

Hi,

In a 2015 VF with LFX engine. Codes came up the other day and I'll be replacing the Evap Purge Solenoid when new one arrives as it appears stuffed.

In the meantime, would someone please help me with a couple of questions as I go through the workshop manual for these DTCs. Thanks to the fella that posted this excerpt from the Manual, I wouldn't have found it. Give my left nut for a pdf with the links working.

Is it normal for the mid section O2 sensors to be stable voltage (unlike the pre-cat sensors)? they drop from about .071 at idle to about .063 at 2500 rpm.
Car is at 650 metres above sea level. Does anyone have the MAP sensor parameters for this altitude/barometric pressure?
Both LT FTRM banks sit above 20% at idle, and get to about 56% at 2500 RPM - is this normal or possible sign of air or vacuum leak? (or is it meaningless with failed Evap valve installed?)

Thanks, JD.

 

[Skylarking]

From a novice, an O2 sensor produces a voltage relative to the air fuel mixture so an O2 sensor measures how rich or lean the exhaust gasses are. The ideal mixture is known as lambda which I believe is at 0.45 Volts.

More oxygen in the exhaust gas than ideal will result in a lower O2 sensor voltage and indicates a lean condition while less oxygen results in a higher voltage which indicates a rich condition.. However, the system isn’t static as the ECU will use the pre cat O2 reading and do the opposite of what the O2 sensor indicates so that the O2 sensor is seen to cycle between 0.15V to 0.85V with a defined frequency (not sure of the number but I’ve heard of 100ms or less but I’ve also heard of q0 cycles per 5 seconds?).

Obviously the amount of fuel the system adds or subtracts will depend on how rich or lean the long term fuel trims (base tables?) are.

The post cat O2 sensors are used to check on the efficiency of the cat converter operation given that the ECU cycles the mixture (pre cat) with a given frequency. The post cat O2 sensor is more stable and should be somewhere in the 500 to 700mV region.

Since the ECU leans and richens the mixture at a given frequency around lambda, the short term fuel trims indicate a bigger lean or rich mixture the is working against. Now (I’m (not sure) a negative STFT indicates an excessive rich mixture (leaky injector?) while a positive fuel trim indicates an excessive lean mixture (air leak) (or it’s the other way around…)…

What impact a failed evap solenoid would have would depend on how it has failed, whether it lets air into the intake, fuel vapour into the intake or is completely blocked…

Id have thought the workshop manual would describe such things but it’s a PITA to navigate. Best to use a PC and display the index pain on the left side pane so that you can click in the various sections and their subsections…

Im sure others will correct my errors so hopefully comments will follow from some members who play with. engine tunes as they’d know more…

 

[goony]

Compared to me Mr Skylarking, you are a master, thanks for your post.

There's a bit more than just the Evap solenoid going on. With the solenoid, I can blow through it in each direction when it is out of the car, carby cleaner * 3 attempts has not rescued it. So i suppose it's letting air into the intake?

Now I can rule the out issues with O2 sensors with your information. The stability of the mids worried me, but the chance of them both failing together seemed remote. Both sets of sensors behave exactly as you described. Cheers.

I found another air leak into the (crappy plastic?) intake from the crappy plastic PCV elbow at the front top of the intake, which was the reason for the questions as I suspected but couldn't find what else was happenning. The o-ring appears shrivelled and not sealing, and took me a while to identify. Wondering if this is a common cause of these intermittant codes that seem to pop up with a few other members? Quick fix is a tiny dab of grease, and seems to have sealed for now. New O-ring to be sourced.

Havent put the scan tool back on it but it still runs a bit rough so waiting on the new solenoid.

If anyone has the MAP sensor parameters for this altitude/barometric pressure it'd be great.

Any other advice welcome too.

Cheers, JD.

 

[wobbles123]

Compared to me Mr Skylarking, you are a master, thanks for your post.

There's a bit more than just the Evap solenoid going on. With the solenoid, I can blow through it in each direction when it is out of the car, carby cleaner * 3 attempts has not rescued it. So i suppose it's letting air into the intake?

Now I can rule the out issues with O2 sensors with your information. The stability of the mids worried me, but the chance of them both failing together seemed remote. Both sets of sensors behave exactly as you described. Cheers.

I found another air leak into the (crappy plastic?) intake from the crappy plastic PCV elbow at the front top of the intake, which was the reason for the questions as I suspected but couldn't find what else was happenning. The o-ring appears shrivelled and not sealing, and took me a while to identify. Wondering if this is a common cause of these intermittant codes that seem to pop up with a few other members? Quick fix is a tiny dab of grease, and seems to have sealed for now. New O-ring to be sourced.

Havent put the scan tool back on it but it still runs a bit rough so waiting on the new solenoid.

If anyone has the MAP sensor parameters for this altitude/barometric pressure it'd be great.

Any other advice welcome too.

Cheers, JD.

If you use cheap fuel...the 02 sensors will gum up....who knows what you are getting with E10 now maybe kero with aviation fuel....cheap fuels will cost you $$$$ in the end....if the 02 sensors are gummed up...it will throw all sorts of codes and cause the vehicle to run erractically.
I have a 2008 VE SV6 ute with 109000Kms and always use E95 or higher...the motor has never been touched except for oil changes at every 8000kms...no timing change issues....only replaced an oil pressure switch.

 

[Skylarking]

If you use cheap fuel...the 02 sensors will gum up....who knows what you are getting with E10 now maybe kero with aviation fuel....cheap fuels will cost you $$$$ in the end....if the 02 sensors are gummed up...it will throw all sorts of codes and cause the vehicle to run erractically.
I have a 2008 VE SV6 ute with 109000Kms and always use E95 or higher...the motor has never been touched except for oil changes at every 8000kms...no timing change issues....only replaced an oil pressure switch.

It’s not cheap fuel per se, it’s the poor legal specification around what constitutes the various standards of petrol.

The fuel quality standards act (2000) and the fuel quality standards regulations act (2019) define what is what. When I went through the regulatory merry go round trying to find how would act on my fuel contamination issue, Consumer affairs points to accc who points to the dep of industry science energy and resources who points to consumer affairs, and round we go again… bupkis from any of them…

But the federal industry regulators did suggest stay away from e10 and 91 as it’s the poorest regulated of all the fuels

 

[wobbles123]

It’s not cheap fuel per se, it’s the poor legal specification around what constitutes the various standards of petrol.

The fuel quality standards act (2000) and the fuel quality standards regulations act (2019) define what is what. When I went through the regulatory merry go round trying to find how would act on my fuel contamination issue, Consumer affairs points to accc who points to the dep of industry science energy and resources who points to consumer affairs, and round we go again… bupkis from any of them…

But the federal industry regulators did suggest stay away from e10 and 91 as it’s the poorest regulated of all the fuels

Yes I am well aware of cheap fuels with modern day cars......how does one know if the service station is putting E10 into the the E95 tank to make a killing ( while world war 3 is about to start ) with a hand shake and some goodies thrown in for the tanker driver....who knows?.......the old days had standard and super colour coded in the eye glass with pink or yellow! ........maybe we will revert to gas bags in a trailer towed behind the car ( world war 2 )....there will plenty of gas available on this forum!

 

[goony]

Thanks for the input.
Interesting subject the fuels.
My mate showed me paperwork from Newcastle docks where the fuel was landed for about 3c per litre, about 10 years ago. So no doubt we are all being shafted at all levels of the industry and governments.
In any event I've put 50K on this engine and E10 without an issue, and have an aftermarket $15 solenoid on the way. The O2 sensors seem to be ok.
I'm betting the solenoid comes from tje same Mexican Bosch factory as the $200 original, or lasts say 30k kms.

 

[goony]

Hi.

New $15 solenoid on. New Oring on. No codes and all fuel trims and O2 sensor numbers normal.

But this solenoid sounds like a bloody excavator with a rock hammer going nuts,even with engine cover on and bonnet closed.

Never heard that before in amongst all the ticks and mystery noises from the engine.

Aftermarket EBay part from $15 to $45
Genuine EBay part $65 to $90
Repco genuine part $212
Dealer genuine part $195

When it shits me I guess I’ll grab a genuine part online...

Thanks for advice above and in other threads on this.