ANOTHER p0171 AND p0174 thread

[kewljay223]

ok so ive searched and looked through all the threads on here and google and am having some trouble...

so ive been having the lean codes on both banks and i finally got them cleared up today. ive only drove around for 15 min so im not sure if its completley fixed or not but the pcm is saying im ready for emissions testing.

i sprayed carb cleaner all over and the only leaks i found were on two injectors. so i replaced the orings and that fixed those leaks but not the codes. i then decided to change the intake gaskets as i couldnt obviously get carb cleaner under the intake. THAT is what seemed to clear the codes.

NOW heres my confusion. everywhere i see is that the STFT and LTFT are supposed to be damn near 0% with some obvious fluctutation. my STFT's are right there. but my LTFT's were pegged at 25% before the orings/intake gasket change. now the LTFT's are fluctuating between 15-24% with an average of about 17% i guess the computer thinks this is ok enough to not throw the codes but im not satisfied with it.

all my hoses look fine and i cant find any leaks. my fuel pressure at the rail is about 55psi while running so im pretty sure the fuel filter/pump, which are new, are just fine. the pressure regulator is also new. the injectors are 50#ers of a 12' 6.0 with less than 1k on them so i think they are good to go.

map and maf sensor readings are where they are supposed to be and i cleaned the maf about a month ago.

all intake piping clamps are tight. i understand if both codes are present this means it should be air entering after the maf but before it gets split between banks OR i have leaks on both banks. but the new gaskets should have fixed the latter....

i also understand that the LTFT takes a little while to settle into range. so should i not worry about it for a while and just keep an eye? or a i missing something?

i dont have a smoke machine and id prefer not to pay a shop 100 bucks to smoke it. only other thing i can think of is TB gasket but the carb cleaner showed no signs of leakage there....

what gets me is that it idles kinda rough. id say its about 70% smooth. is this normal? are my readings ok? or is there possibly something else thats causing the roughness that has nothing to do with a vacuum leak?

sorry for the lengthy post. just trying to give as much detail to help in the diagnostics. im ready to take it to the ref for testing and dont want any issues. any help would be awesome. thanks!!

[jeast]

Did you verify you have spark on all cylinders? Are the O2 sensors reading the same on both banks? Any PCM Mods?

[Oldspimp]

Run it with a fuel pressure gauge for a while to make sure the pump is not flaking out.

[farmtruc]

When the stock setup is changed in anyway, all ideal data and situations do not apply.
Even if those injectors are stock from another GM vehicle and the injector flow rate and other injector tables are adjusted in your pcm; there will still be some adjustment needed.
Granted 25% ltrims are high even if all the injector data is correct with NO fine tuning; so there could be an issue.

IF the air intake tube or maf has been modified, turbulence and uneven airflow can cause high ltrims. Be sure the o2 sensors are toggling correctly, this can cause high ltrims.

IF you're 100% sure there are no leaks or any issues, those high ltrims can be lowered by adjusting the tune.

Basically what I'm saying is; theoretical tuning doesn't equal real world tuning.

[kewljay223]

thanks for the replies. no i didnt verify spark but its not running THAT rough. it just kinda stumbles a little bit every once in a while kinda like a mild cam or something. nothing major. highly doubt its missing. im sure i would notice that. as for the fuel pressure, it only fluctuates +/- 2psi under throttle no matter what RPM.

as for pcm mods, nothing really. just for the bigger injectors, 80e, and a "slight performance tune" whatever that means.... brandan from lt1swap did it. i told him to keep it basically factory due to emissions. he also made it so that the readieness codes show pass.

ive checked this thing pretty well. im pretty sure i have no vacuum leaks and the fuel system is up to par. i did put the aftermarket intake pipe/filter on which wasnt "tuned for". could that be part of the extra air its seeing vs the stock intake?


i think i understand what your saying allen and it makes sense. if im understanding correctly, higher fuel trims means more fuel being pumped in. i assume this will affect my gas mileage negatively??? could you explain how lowering the trim in the tune would "fix" the problem? i mean if you drop it, that would be less fuel with the same amount of air coming in since i wouldnt be changing anything else physically.... wouldnt that lean it out even more than it already is in turn being a bad thing?

here is a snap shot of my PID's this is at idle but after i had driven around for about 50 miles today. still no codes... as you can see in the max and min coulumns, yes all the o2 sensors are fluctuating like they are supposed to be. and you can see the STFT's are really close to 0. im leaning towards what allen is saying...im betting it just needs to be adjusted in the tune...

[farmtruc]

Ltrims tell us how much fuel the PCM is adding or trimming.

If the ltrims are within tolerance then the engine isn't run lean or rich; because the PCM has taken care of adjusting fuel delivery.
Ppl misunderstand ltrims and right away comment how lean an engine is running if the ltrims are high.
It's not ideal and should be adjusted tho.
Lots of variables will change ltrims; they're meant to go up and down.

Increasing fuel pressure will bring them closer to zero.

Strims will be within tolerance most of the time.
As they average out they will build the ltrim data.
Strims are the result of immediate fuel changes and ltrims over time.

[kewljay223]

so are you saying that im worrying about the high LTFT for really no reason then? meaning there is nothing majorly wrong? your a pro tuner who has unanimuous respect from this site which which gains my faith in what you say. im no pro and am at the very beginning to wrap my head around this. so i do trust what your saying for sure. i just feel they are a bit too high since they are super close to the maximum tolerences...

but if you say that its ok and an adjustment in the tune will properly take care of it, then i will let this worryiment that i have go to rest. lol

[farmtruc]

Ideally you want ltrims to be 0%, however, with the surroundings always changing they will go up and down, which is normal.
Having the ltrims too high narrows the ability for the pcm to adjust. If the ltrims are 17%, then the pcm only has 8% correction left. If the ltrims are 3%, then.... 25% being max; then the pcm sets a code and the ability for the pcm to adjust halts and if the engine is still lean, then the potential to have a lean condition.

The ltrims should be adjusted. As modifications are added ltrims will get higher and higher. The pcm's tables need to be adjusted to account for more fuel required by the engine.
This allows the pcm to think x amount of fuel is normal.
Even something as simple as a cai will make the ltrims change.

If you get those ltrims lowered then the lean shakiness may settle down.

[kewljay223]

oh man that last post really drove it home. that makes complete sense and im betting thats whats going on then as im 99% sure everything else is in good shape. that was driving me crazy all weekend!!! trying to hung vac leaks and fuel problems... lol oh well. i really appreciate you taking your time to explain that. and in somewhat lamens terms too!!! haha. ok well then im not going to worry about them as there is a reason they are high and just need to be adjusted in the tune. i will be calling the Referee station tomorrow to make an appointment for next week now that i know this probably wont throw any codes for the Ltrims. once again, you are the man!! thanks.

[farmtruc]

No problem. Glad it helped out.