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Discussion Starter #1
Have a 2006 HSE. P0171 and P0174 showed up a about a month ago (at the same time). Got a smog need to pass in a couple weeks so have started to troubleshoot. After a bit of research, I think I've narrowed it to MAF and/or fuel supply.

Here's why...
1) At IDLE long term fuel trims are around 5-6%, but at 2500-3000 rpm 40-50% load, the trims go up to 15-20%. To my understanding, this rules out intake vacuum leaks?
2) I do hear some sort of hissing sound on passenger side of engine. Not sure if this is normal or indicative of a leak. I sprayed carb cleaner all around hoses but never noticed a change in engine's rpms.
3) The car does idle a bit rough, and has occasionally shut down.
4) The fuel gauge over reports fuel supply, which has caused me to run out of gas a few times while the tank claimed there was 2 gallons remaining.
5) Because of 4, my understanding is that this wears down fuel pump.

I have ordered a new MAF, fuel pump, and fuel cover with filter.

Do you have any other items I could check out. I am a novice mechanic, but willing to troubleshoot.
 

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Discussion Starter #2
re: 2006 PO171 & PO174 Lean Codes

Update: Just found MAF spec at 2500 RPM is supposed to be ~16 g/s but mine show as ~60 g/s. I have sprayed the MAF sensor with CRC and new one ordered.
 

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2006 PO171 & PO174 Lean Codes - Help with Diagnosis

Update: Just found MAF spec at 2500 RPM is supposed to be ~16 g/s but mine show as ~60 g/s. I have sprayed the MAF sensor with CRC and new one ordered.
Wouldn’t you be running rich if the MAF was reporting more air entering the intake than actual? I would think the ECM would in turn add more fuel to match the erroneous MAF readings? I would also be looking at fueling issues. An obstructed/dirty fuel filter or failing fuel pump would lead to lean codes. Have you checked fuel pressure at the rail?



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Re: 2006 PO171 & PO174 Lean Codes - Help with Diagnosis

Agreed, it would. Not sure what was going on with that MAF sensore. But, I replaced it, cleared codes, and 100 miles later CEL has not returned. The long trims are close to 0.

BUT now I can't get the o2 sensor to set as ready for inspection. I've done drive cycles A-D (D twice) and still no love. I've pulled a graph of the o2 sensors. Upstream (wide range) seams to bounce around lambda with appropriate deviations from WOT. Downstream (sensor 2 banks 1 and 2) stays mostly flat at .8v. No codes. Would this warrant a replacement???
 

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re: 2006 PO171 & PO174 Lean Codes

No, the downstream sensor should be flat. But I am not sure about the .8 volts. That would seem high to me.
I am not sure what state you reside in, but in New York, and numerous other states you can pass emissions with one readiness code not set as long as all the others are identified as “ready”.


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re: 2006 PO171 & PO174 Lean Codes

I'm in California...we have the same 1 sensor not ready rule rule. Didn't mention it before, but the evap is also not ready and I'm not sure I have any chance at figuring that one out! So I have focused on the o2. I also just learned that the drive cycle is supposed to be done without the OBD scanner in...so will give them another round tomorrow. A -D?? If that doesn't work, I'll replace the upstream sensors and cross my fingers.
 

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Hi, I'm a very new member but I am hitting the ground running. Have you checked the crankcase valve? When its stuck open or closed it often throws those codes. I'd also check the PCV line that goes from I believe the PCV valve to the throttle body. These become extremely brittle over time and develop cracks or breaks large enough to throw the codes. I had a similar issue on a 2003 Jaguar STR which has almost the exact same PCV valve. I replaced the line running to the TB and it solved my P0171 and 174 codes.
 

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re: 2006 PO171 & PO174 Lean Codes

Funny. I did replace the PCV valve as it seemed like it wasn't working well with my homeade blow air test. Also replaced the MAF sensor. codes are long gone. Cannot get emissions monitors to set as ready. just replaced all 4 o2 sensors today and repeated drive cycles. maybe I don't know how to do the drive cycles. ack...
 

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2006-2009 Range Rover MkIII / L322
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re: 2006 PO171 & PO174 Lean Codes

Hi, I'm a very new member but I am hitting the ground running. Have you checked the crankcase valve? When its stuck open or closed it often throws those codes. I'd also check the PCV line that goes from I believe the PCV valve to the throttle body. These become extremely brittle over time and develop cracks or breaks large enough to throw the codes. I had a similar issue on a 2003 Jaguar STR which has almost the exact same PCV valve. I replaced the line running to the TB and it solved my P0171 and 174 codes.
very good gold advice. I been there. Checked and replaced everythinf could be leak finally i saw the crack on long pcv line from the pcv to the tb.
 

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re: 2006 PO171 & PO174 Lean Codes

I battled these codes on my 2004 RR with M62 (after head replacement) and on my Jag with your same motor (after valve cover seal replacement).

Both were caused by air leaks from loose clamps, aged hoses, and getting old parts to seal (replaced them). You need to look at everything air related after the air filter (even the air filter).

Typically P0171 and P0174 codes are caused by air leaks. Go over everything and if you can do a fuel trim scan - that usually confirms air leaks.
 

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I agree. A tiny hole or crack can have this adverse issue. Like he said check everything from the air filter all the way to the throttle body, and on. It is air related.
 

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How do I check to see if my pcv is working?

If I remove it with it connected to throttle body, should it always suck from bottom?

Think it closes with negative pressure but I cant provide that, can i?


Hi, I'm a very new member but I am hitting the ground running. Have you checked the crankcase valve? When its stuck open or closed it often throws those codes. I'd also check the PCV line that goes from I believe the PCV valve to the throttle body. These become extremely brittle over time and develop cracks or breaks large enough to throw the codes. I had a similar issue on a 2003 Jaguar STR which has almost the exact same PCV valve. I replaced the line running to the TB and it solved my P0171 and 174 codes.
very good gold advice. I been there. Checked and replaced everythinf could be leak finally i saw the crack on long pcv line from the pcv to the tb.
 

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You will easily be able to tell if your PCV is bad because your engine will either misfire or will be running very lean. If you have an OBDII scanner or something that shows live data you can check some info. I recommend the BlueDriver which you can setup to your phone or tablet. This will allow you to see your short and long term trims and your fuel and air mixture. Another telltale sign of a bad positive crankcase valve is if you find oil inside it. Other than that if you want to check for leaks, spray some brake clean or carb cleaner down the length of the PCV line starting from the valve to the throttle body while your engine is running. If you notice a change in your idle when you're spraying this line then you can pinpoint a leak to that area of the pcv line. With your engine running, there should be strong suction in the pcv. If you think your PCV is bad and have already determined it is not clogged or stuck open and you're having the P0171 or P0174 codes then check vacuum lines. I would first check the pcv line.
 

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re: 2006 PO171 & PO174 Lean Codes

I had both. Bad pcv line and bad valve.
Broken line was very hard to diagnose, crack was rear the tb. I replaced the line and everything goes fine
to checking this long line is very easy just remove the hose and check it visually

bad bad very bad valve is easy to see. Hissing noise isn’t a catch. I replaced it week ago the new one is also noisy but just a little bit lesser
with broken pcv valve comes oil consumption and blue smoke on cold stars.
I rebuilt my engine year ago gave my soul and i was sure the reason of blue smoke isn’t the varlve stem seals or piston rings. Replaced the valve woth an oem part and everything is good so fsr
 

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Interesting, I just went ahead and replaced the pcv and thoroughly cleaned maf sensor. And inspected all but one line for leaks (attached). I don't know how to disconnect this line or where it goes.
I m leaning toward the maf having slow response due to build up... that's why when I drive far on the highway, fuel economy returns to normal and the codes are always thrown on a steep on-ramp.
 

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re: 2006 PO171 & PO174 Lean Codes

I you done everything and the codes cames back you have to update Ecm software i mean computer soft
first calibration was very sensitive on misfires and air leaks.
Maybe your are leaking in normal rates.
Dont forget to check injector o rings
i see you have 4.4 jag engine tb is on different location.
One time i had leaks on the main air tube, leaking part was metallic bracket
 

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2002-2005 Range Rover MkIII / L322
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pull one of your vacuum hoses and smoke test the intake manifold. I had this problem on my 04 and found an air leak at the throttle body that I fixed with some permatex gasket maker.
 

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Several things to remember here. First, the MAF has a parameter to meet at certain rpm and engine load. High MAF readings will tell the computer to add fuel, but only to its maximum, which is typically 15-25%. More than that, the software will not add more fuel due to the duty cycle of the injectors. Since they have a limit to their duty cycle, more than what is recommended will overheat the internal solenoids. My first thought is to the hiss you heard. Before going any farther, try to locate its cause. It will likely be a vacuum leak, and the O2 sensors are responding to the extra O2 in the exhaust. This will tell the ECM to add fuel. It will add fuel to its previously described limit. Some of these codes may be sympathetic, meaning they occur due to other sensors and other limits being exceeded. All of these parameters have "windows" to monitor, and if they are exceeded, the ECM can get confused, and set other codes. Try clearing the codes, and locating the source of the hiss. Let's not start chasing our tails Ray
 

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My gut tells me you have an air leak. When you go heavy on the throttle on the entry ramp is the reason. More gas = more air needed.
 
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