p0171 and p0174

Synyzter

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OK, so last week my truck was throwing these codes. I looked over all the vac lines, and everything was fine. Had the MAF tested and it was junk and causing my truck to stumble in the midrange. I cleared the codes and they stayed off. Now I replaced the MAF with a brand new stocker and added a CAI. The codes just keep coming back. All the hoses and lines on the intake are super tight and the MAF is perfectly fine. The only other thing I can think of is maybe its time to change the fuel filter? My truck has no rear cats, could the oxygen sensors finally have realized that they are missing (rears have been out for 4 months and a SES light never came on). As far as performance goes, everything seems normal. What are my possible problems before I wind up throwing money at shit I don't need?
 

Bob_Kurgan

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these are codes that will pop up with the CAI and no tune.. your car is running VERY lean now and i wouldnt go WOT without a tune.. you are living on limited time.

for these codes to pop up, your STFT have to exceed 25%, which means your truck is running at least 25% leaner then it should...
 

sleepercobra

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these are codes that will pop up with the CAI and no tune.. your car is running VERY lean now and i wouldnt go WOT without a tune.. you are living on limited time.

for these codes to pop up, your STFT have to exceed 25%, which means your truck is running at least 25% leaner then it should...

this cant be good...
 
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these are codes that will pop up with the CAI and no tune.. your car is running VERY lean now and i wouldnt go WOT without a tune.. you are living on limited time.

for these codes to pop up, your STFT have to exceed 25%, which means your truck is running at least 25% leaner then it should...
they popped up before the CAI was even installed. i've made 1 WOT pass from 0-60 but other than that, i've been fairly light on the pedal to keep it safe. I'lll be pulling the blower off in 2 weeks to clean the intercooler, change the plugs, and changing the SC belt, and seeing if the PCV hose behind the blower is cracked. thats the only vacuum leak I can think of. I don't get why these trucks are so finicky. I see a million other people run CAI's with no tune and no issues.
 
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Well, fuel filter and MAF have been replaced. I can't find a vacuum leak anywhere, so it has to be the PCV hose behind the blower. thoughts?
 

SVTLSC

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there are alot of things that can cause this. eventhough it sets a code and the fuel trims are off its not damaging anything because the computer is correcting it so it tuns fine. my truck throws them sometimes, i clear them and they go away for a while. Personally if it was me i would check to see what it was doin with a scan tool, watch the o2 sensors with a dvom and see what the fuel trims are at when it sets the code. also check the freeze frame see what temp, what the maf is reading when it does it. im not sure if the Ls have the ame problem but all the non supercharged 5.4L engines have a bad problem with the intakes leakin so that could be your prob too. Give me a call if you want i will help you out
 

Bob_Kurgan

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there are alot of things that can cause this. eventhough it sets a code and the fuel trims are off its not damaging anything because the computer is correcting it so it tuns fine. my truck throws them sometimes, i clear them and they go away for a while. Personally if it was me i would check to see what it was doin with a scan tool, watch the o2 sensors with a dvom and see what the fuel trims are at when it sets the code. also check the freeze frame see what temp, what the maf is reading when it does it. im not sure if the Ls have the ame problem but all the non supercharged 5.4L engines have a bad problem with the intakes leakin so that could be your prob too. Give me a call if you want i will help you out
sorry, i have to disagree with you... generally with a stock maf, whatever correction is happening at lower maf voltage is also off that much at high maf voltages... so, with the change of a CAI, if the STFT and LTFT started correcting 15-25%, its linear on the rest of the maf transfer function..

If he is throwing these codes and there is an issue with the CAI requiring more fuel, he could possible hurt the motor by leaning it out at higher RPM.. I still suggest that it get taken to a reputable tuner and tuned for the newer mods.. MAF's are funny things and even looking at them funny can make some drastic issues.. Im not saying bring it to me, but bring it to someone to tune..
 
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Synyzter

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Bob, you are the guy i'm going to have tune my truck. However, I had this issue before I even put the CAI on, thats why i'm trying to cover all the bases. only thing left is the PCV hose behind the blower that you can reach without taking the blower off. I'm looking to add a mafia and maybe a 6lber before I bring it to you for the final tune. no sense in spending all that tuning money for just a cai and a catback
 

Bob_Kurgan

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Bob, you are the guy i'm going to have tune my truck. However, I had this issue before I even put the CAI on, thats why i'm trying to cover all the bases. only thing left is the PCV hose behind the blower that you can reach without taking the blower off. I'm looking to add a mafia and maybe a 6lber before I bring it to you for the final tune. no sense in spending all that tuning money for just a cai and a catback
all you need to do is get a propane torch and turn the gas on and run it around ANYWHERE you think a vacuum leak might be... if the RPM's jump, then you have found the leak... obviously, dont "light" the torch LOL.. jsut turn the gas on... i would also recommend brake cleaner, but that makes a mess.
 
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Synyzter

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stupid question...but would i find that torch at ace hardware or something?
 
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i figured thats what it was, just assuming i'd find it locally at a hardware store
 

SVTLSC

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sorry, i have to disagree with you... generally with a stock maf, whatever correction is happening at lower maf voltage is also off that much at high maf voltages... so, with the change of a CAI, if the STFT and LTFT started correcting 15-25%, its linear on the rest of the maf transfer function..

If he is throwing these codes and there is an issue with the CAI requiring more fuel, he could possible hurt the motor by leaning it out at higher RPM.. I still suggest that it get taken to a reputable tuner and tuned for the newer mods.. MAF's are funny things and even looking at them funny can make some drastic issues.. Im not saying bring it to me, but bring it to someone to tune..
ok makes sense. ive never tried that propane trick will have to try that. i usually use a water spray bottle and when it starts to miss you find it
 
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OK, so once again today, I decided to go over the p0171 codes and the p0174. Today, only the p0171 code showed up. I checked all the vacuum lines including the one behind the blower. No leaks. The MAF and fuel filter are brand new, as well as the CAI (was throwing code before intake).

Now, for 4 months i had no rear cats into the stock exhaust with no problems or codes. I put a muffler on to replace the stocker. The day after I put the muffler on, roughly 2 or 3 drive cycles of 1+ hours, the SES light came on with these codes. Now, if my thinking is correct, is it possible that the increased flow of the muffler finally triggered the rear o2 sensors to falter from the lack of rear cats, thus causing the truck to think its lean?
 

SVTLSC

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no cats wont set a lean code. it would set a p0420 or 430, or one for o2 sensor cycing
 

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