CaptainXS

could excessively negative fuel trims cause a p2178 engine code?
"P2178: System Too Rich Off Idle Bank 1"

and then what would cause excessively negative fuel trims... i am talking like -18 LTFT on a good day... and sometimes into the -20's...

I can be a bit dyslexic at times... but doesnt negative trim mean it is removing fuel from the tables to maintain stoich... so in other words, your engines mapping is too rich and the O2 sensor reports it as overly rich, and is subtracting fuel to keep things where they should be....

if that is the case... then wouldnt COLD winter air... outside temps in the 20-30's mean more dence air, thus fuel trims should be higher (positive trim) to add fuel to keep up with the higher concentration of oxygen in the air.

Wouldnt that also be true for performnace mods? If i added a better filter, and better flowing exhaust and anything else to let the engine breathe better... i should be increasing the air flow, and thus should see higher (more positive) fuel trims...... (under cruise situations of course....) and this is why people with alot of airflow mods need tuned... cuz they would be running too lean cuz of more oxygen, for a fixed amount of fuel in WOT.

so if all that is true.... then how the heck am i running too rich... when it is 20-30 degrees out... and i just installed a bunch of performance mods. Kinda thinking something is out of whack. or i have my logic backwards....

I am thinking maybe i have a vacuum leak somewhere... and i am losing metered air... so the car thinks it is getting X cfm... so it gives it Y fuel... but only X minus 2 reaches the cylinder, so it registers as rich?


and this is all regarding a 08 SS Turbo.. LNF. in case it matters...
and just curious... I know the LNF has a MAF and a MAP... but anyone know which one it relies on for fuel calculations? or is it some formula combining both readings?

unijabnx2000

iTrader: (1)

whats your mileage?

CaptainXS

Less than 11,000. Practically new

BYT*SS*TURBO

iTrader: (6)

Your sig says you Hp Tune...If you have a LNF with a Intake, why wouldn't you just tune the MAF so that issue goes away??

CaptainXS

Alas, I can do that... but i just put the intake on last week. and i have not even licensed my car yet on hpt. i wanted to observe what all was going on first before i just "tune it away"

And it seems slightly backwards to me... i would think that i should be too lean if anything. not too rich. I understand that the maf readings can be skewed if the diameter of the pipe the MAF is in changes... but i checked and my OEM diameter is nearly identicle to the diameter of my intake now... both setups are very similar as far as size and bends etc of the airway past the MAF... so the only thing that changed should be the the actual air flow. So i wasnt sure that maf scaling was in order.

The fellow i got the charge pipes from had welded an atmospheric BOV on, just past the turbo in the hot pipe.... (sits directly above the cam cover)... he swore to me that it worked just fine and he never threw any codes or anything with it... I didnt believe him... but i tried it anyway... plumbed it all in... and sure enough i got codes on the first drive. Was sure it was the metered air escaping from the BOV, which would indeed cause a rich condition. So i disconnected the vacuum source to the BOV. plugged everything up tight.. cleared my codes and tried again....
codes were gone for a while... but eventually came back under heavy acceleration at one point. I assumed this was from the boost pressure overcoming the spring pressure of the BOV, allowing air to leak out... but after clearing the code... i noticed it would come back randomly, even without and boost pressure at all... so i am starting to doubt it is the BOV at all... i plan to remove it entirely and block off the flange, or just cut the flange off and weld it back up. but for now i will deal with it. But the only trend i noticed across the board was that every log i have done since installing the intake and downpipe and charge pipes is the crazy negative fuel trims. the engine always stays pretty spot on stoich the whole time... but it takes tons of trim to get there.

so it just seems odd to me that the crazy trims i am seeing could be caused by a few bolt ons...

so i want to make sure there isnt something else wrong before i just go tuning it for a defect.


oh yeah... and i am trying to get an exhaust on there and tune it all at once... instead of re-doing it several times as i add parts.

BYT*SS*TURBO

iTrader: (6)

The 1 car I tuned with a Dejon intake had the worst breather adapter piece Ive seen yet on it. I would check yours to make sure it isn't leaking.

Otherwise, fuel trims out of wack is the norm for a Intake on a LNF. Tune the MAF tables, you need to regardless..

CaptainXS

Not sure which breather adapter you are refering to.... but the MAF mounting plate did seem a little "home brew" like a big steel rectangle welded on, and the actual MAF hole itself looks like they cut it out with a drill or dremel or something... not at all nice and machined and professional like i expected it to be... but it still seemed to mount up alright, and i did not detect any sort of leak.

BYT*SS*TURBO

iTrader: (6)

There is a breather line that connects to the Intake. It has a fuel line style connection. The Dejon SRI I saw just slid into place, didn't lock! Wasnt great

CaptainXS

Oh yeah... that breather... yeah it just slips on... no lock at all... but it is a pretty snug fit... and i have never seen it so much as budge... it isnt under boost or much vacuum at all... so i dont really see why it would need to lock.. i dont see any chance of it popping off. so never really figured it as being a source of any of my problems.


And again.... i was just reading up on other people who have had issues with intakes throwing off thier AFR's... but as you would expect... everyone else gets "LEAN" codes... which makes sence... so how is it that i am too rich?

There has to be something more than just a MAF out of calibration.


and am i wrong in that negative trims subtract fuel to lean out a rich mixture? So if i am indeed running rich... i should see negative trims at cruise (or in the case of the LNF which is wideband based, i should see them all the time.) or might i have that backwards?

BYT*SS*TURBO

iTrader: (6)

I would get a water bottle and spritz it on that fitting, see if the idle jumps! At least rule that out

CaptainXS

water bottle huh? that is a new one... i always heard to use like starting fluid... or a unlit propane torch.... then if it sucks in any of the flamible gas, it should speed up the idle for a blip... no leaks = no responce...

but i tried the propane torch deal.... and the engine didnt respond to anything at all... not even when i shot the propane straight into the airfilter...


I assume the water bottle trick is not so much to let it suck up the water, as it would be to momentarily "plug" a leak.... right?

BYT*SS*TURBO

iTrader: (6)

Just something to make a change if it is indeed leaking. Starting fluid is another good one, but I just dont like spraying that **** around or into the air lol.

Do the same with the MAF mount, maybe that is leaking. Just things to check to make sure everything is good, then tune the MAF and Ill bet your problems go away!

CaptainXS

ok well using the water spray bottle... i got no fluctuations in idle at all at the maf or breather or any vacuum source i could shoot at... checked all my couplers and clamps... everything seems fine.

I also double checked the inside diameter of the OEM tubing where the MAF mounts, and the ID of the current intake where the maf sits... is a whopping 1/8" of an inch different.... that is 2 of the smallest lines on a normal tape measure... and the intake is actually smaller than the OEM plastic tubing. So technically the MAF should get MORE air passing thru it.. making the MAF register more air due thus thinking it is LEANER than it is. and i hear that the factory airbox restricts more than 10hp worth of airflow.... so all that extra air coming in..... and the smaller maf passage... i SHOULD be CRAZY lean. but i am showing rich... i am sooo confused.....

I know I know... "just re-calibrate your maf" but i have spent hours and hours tuning anf re-tuning before all for nothing, because i was tuning over the top of a problem....

This time i would at least like to figure out why i am showing rich when i should be lean before i go changing the tune and making more variables.

so if any of you would just be so kind as to brainstorm with me here...

How can i be -20 Rich?

dirty air filter? clogged intercooler?
even a leak should fluctuate... i would suck in extra air at vacuum... and leak air under boost... so i would be rich sometime and lean other times... but i am crazy rich across the board under boost and at idle/cruise. i dont recall any places where i was normal, let alone lean...

This is from a description of how a P2178 is detected... "The PCM monitors short term fuel trim (SHRTFT) and long term fuel trim (LONGFT) during closed loop fuel control at off-idle. If the LONGFT or the sum total of these fuel trims exceed preprogrammed criteria, PCM determines that fuel system is too rich at off-idle."

so safe to assume that my CEL is entirely based on my fuel trims... so then i ask, why are my trims so negative... i looked back to a log i did before the mods... and even then i was negative... but not nearly so much... maybe 5-10... but nothing like i am now.... even when i first got the car, my tune shows from -3 to -6 LTFT in 77 degree weather....

any ideas? dirty MAF maybe?

CaptainXS

ok i have cleaned my MAF sensor... it didnt change things one bit....

i did some logs and some comparisons....

before i did anything under the hood... bone stock....
i was getting 0.37 lb/min at an idle of 800rpm.
and 16.7 lb/min under heavy accel at 3200rpm 50mph and 83% throttle

after all the mods in my sig... short ram intake, 3"catless dp, hahn charge pipes....
i am getting 0.46 lb/min at an idle of 800rpm.
and 17.5 lb/min under heavy accel at 3200rpm 50mph and 83% throttle

So if i am showing that much MORE AIR now... how is it still saying i am too Rich? and why are my trims cutting fuel? Everyone else in my situation seems to be LEAN and adding fuel...

May i remind you all... i have not TOUCHED any settings on the car... i have not tuned it at all, only things that have changed are the parts listed....

anyone.... anyone..... bueller? anyone....

JTob

Ok, your P2178 code is set by your 02 sensor. And your 02 sensor is the CAUSE of your negative fuel trim. Meaning that the 02 does not see any air in the exhaust. When the 02 does not see air in the exhaust, it thinks that the car has enough fuel to use up all the air, and then some. At this point, you can eliminate unmetered air (your right, it would cause lean codes) you can eliminate unburnt fuel or lack of combustion ( again you'd see lean codes). All in all, seeing rich codes generally means one of 2 things:
1) You have a bad 02 sensor
2) You have an overfueling injector

So how does the car run with the fuel trims at -20?

CaptainXS

technically... i think the code is set by the fuel trims, which are set by the O2, as compared to the MAF tables.

Correct... in the event of CRAZY rich conditions... but i am doubting that even in mixtures that might call for -25 trims it is to the "complete lack of oxygen" point...

I agree with you here in most situations.

doubtful... seeing that the car only has 10k miles on it.... and it worked just dandy before i installed my downpipe, intake, and charge pipes.

ehh... same as above... doubtful on this new a car (and these being direct injection, i doubt it is too easy to clog up some thousand PSI), and since there was no problem with it before the upgrades...
it runs just fine all the time.... no sluggish, not jumpy, just smoothe

the wideband seems to register just fine, and i see no irratic behavior like one would expect from a faulty injector or un-even cylinders..


I was just reading up on another forum, and it sounds like there have been a few other people experiencing extremely negative fuel trims like mine after installing a catless DP. I would think it wouldhave the opposite effect... but maybe the lack of backpressure allows the gasses to pass by the O2 sensor faster, so it doesnt read as much oxygen, thus making it read leaner than it actually is?

just thinking out loud...

but in a case like this... i could just re-tune the maf... but it sounds like the maf may be more accurate than the O2... so i would be adjusting the wrong part.... right?

DarkCobalt13

How has fuel consumption been?

BYT*SS*TURBO

iTrader: (6)

I was getting -20 - -23% when my O2 went bad. While I think 10K is pretty new for it to go bad, it does sound possible! They're $60 from GMPartDirect.com. (PN#: 12589380)

CaptainXS

It seems to be about the same as always.... i almost always drive with my display set to instant MPG... and i am usually right around 25-30mpg at freeway cruise... and like low-mid 20's city cruise...
I typically get about 320-370 miles to an average tank of gas.
It all depends on how i am driving... or how much idling or heavy accel.... But it all seems right on.

As i mentioned, when logging the car, the wideband seems to register normal... almost consistantly right around 1.00 lambda... and then when dfco kicks in it jumps up to 1.99 or something, then right back to 1.00 when i hit the gas again.

oh.... also... if i "clear codes" while driving/logging... the trims all jump back to 0... the WB jumps a tad rich... the car seems to loose a lil power... and then very quickly the STFT's start climbing fast... and eventually get to the point the LTFT were... and then after a little while the LTFT takes over and then the STFT goes back to normal range, and the LTFT is way rich again.... and eventually the code gets thrown again... (which puts the car in a limp mode and cuts out the turbo almost entirely.... which really sucks...)

i am just trying to think things over here....

how would a catless DownPipe cause an O2 sensor to read RICH?

as mentioned, it measures amount of oxygen... more oxygen = more lean. less oxygen = more rich.

So... assuming everything before the turbo is pumping more air... there should be more or at least the same amount of oxygen at the turbo here.

As i understand it, the WBO2 is located up near the turbo... somewhere upstream of the DownPipe... (the only O2 on the DP is the post cat O2, and there are none on the catback portion...) so the WB must be on the turbo or the exhaust manifold.....

So... what could be starving the sensor of oxygen? it isnt going to be anything like the MAF... where changing the size of the tubing will effect the readings... and the area around the O2 is untouched... only thing that has changed is the downstream restrictions (CAT and crimp for post-cat O2 bung removed).

so how could this skew readings?? where is the oxygen going?

any ideas?

JTob

Ok if your fuel trim is -20ish and the car runs just fine then odds are that the fuel cut is compensating for something. No car will run well with that much fuel cut unless it needs fuel cut.

If I we're you, I'd be having a look at my plugs, looking for burnt or fuel soaked conditions.

CaptainXS

wow... well i figured it wouldnt hurt any... so i pulled a plug. I figured they would look fine, since the engine always adjusts and brings the AFR's to right around 1 lambda... i figured the plugs wouldnt tell me anything.... I was wrong....



Yeah i would say that is kinda rich.... totally black around the outter ring... some flaking dry carbon deposits... nothing wet.... but the center ceramics actually appear to be a "dark chocolate" or "coffee bean" color... which tells me we are a little too rich at WOT... but definately seem rich under cruise....

So... of course now... i have to ask.... is this the MAF or the wideband screwing up? cuz as much of the time as the car is at 1 lambda... (after -20 trims...) i figured the plugs would be fine... but they are not... so could my O2 be making the engine THINK it is running just dandy... when it indeed is running rich...

ah... so many choices... and do i just go buy a $60 O2 and see what happens.... or do i take it to the dealer as it only has 10k miles on it... (but risk them yelling at me saying i did it with my mods)

mmcgee123

iTrader: (1)

Ur o2 isn't bad check the voltage at idle off idle etc bc of the intake and the maf location compared to stock the computer might be thinking it's gettin more air then it really is So it's scaling the injectors which could cause the over rich condition tune it for the intake

JTob

Did you check all your plugs? If only one or two looks like that, Id say injectors. The reason I dont see it being the o2 is because it adjust fuel to -20 and you say the car runs fine. So the O2 is doing its job.

CaptainXS

just an update... broke down and registered the cobalt on HPT... calibrated the MAF and nudged a few of the other tables....
After calibrating the MAF... the trims seem to be right on the money... but i still want to get some more miles on her and take a look at the plugs... make sure i am not going too lean now (if i calibrated around a faulty sensor)...

I still would love to know WHY it was so rich after all those parts.... i hate to "just fix" something without knowing what caused it in the first place. that is the kinda job you end up "just fixing" over and over again.... I just like to know the why before i get into the how.

Also... what AFR/Lambda do you guys find that the LNF likes under throttle? I am amazed that they have it running 14 from the factory thru 90% of the table.... that is just nuts... but maybe DI likes it that lean... that is why i am asking...


Also... i thought these turbos were supposed to max out around 22psi? first test drive after the tune i was hitting 25psi regularly, and seeing peaks significantly higher... almost 30 a few times...
and i wasnt really trying....

and why is it that i dont have an option for overboost protection disable in HPT.... everyone else seems to have it.... but also... it seems like no one else has trouble logging into a decending order histogram... (like the MAF CAL... starts at 500000 and goes down... my HPT refuses to fill in histograms like that.) Do i just have a bug? or is there an update i need or something?