Sharkey

iTrader: (1)

about 2 weeks ago my car popped a p0171. i had a look at the freeze frame data and cleared it off, didnt come back till yesterday. did the same thing, and again today its back. the freeze frame data is showing the code setting under decel conditions (coasting down in gear) every time, wideband shows lean as you would expect under decel. the LTFT is showing 17.9% most of the time under decel, freeze frame shows over 18% every time it set (i know it sets the code if it goes over 18%). 02 sensor is also switching as it should.

my setup
-05 ss/sc
-stage 2 with 2.9" pulley
-airbox mod with CAI piping and dryflow filter
-clear image header, custom catless downpipe and cat back
-dual pass/cobra
the car has had this setup on it for almost 3 years, aside from when i bought it 2 years ago it has a TOG header. its never thrown codes, never had any problems

i have checked out the usual things, found no vacuum leaks, cleaned the maf, air filter is clean, intake piping is not rubbed through (yet). i might have an exhaust leak, however its at the end of my downpipe and should have no effect on the o2 readings.

anyone have any ideas?? i know this is a common code with modded cobalts, but being the car has gone so long with no issues with the mods i have, i cant say a mod is causing the issue.

Wolf117

pretty sure its just from having anything but a stock intake. not positive though

Sharkey

iTrader: (1)

its actualy an airbox mod with a cut up aftermarket intake. the maf is still in the factory airbox. the car has been running like that for 3 years now, if it was causing the problem it would have shown up sooner.

rukkee

iTrader: (3)

Here are some idea's from GM's service information

Is the Long Term FT parameter greater than the specified value? (18%) Go to Step 4

Step 4
1. Operate the engine at idle.
2. Observe the Heated Oxygen Sensor (HO2S) parameters with a scan tool.

Does the scan tool indicate that the values are within the specified range (40-900 mV) and fluctuating?



Diagnostic Aids
• Test for fuel contamination. Small amounts of water can be delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
• The system will go lean if an injector is not supplying enough fuel.
• A lean condition could be present during high fuel demand due to a fuel pump that does not pump enough fuel, a plugged fuel filter, or a restricted fuel pipe.
• Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Intermittent Conditions .

• Missing, loose, or leaking exhaust components
• Vacuum leaks at the intake manifold, throttle body, and injector O-rings
• The air induction system and air intake ducts for leaks
• The crankcase ventilation system for leaks
• The evaporative canister purge pipes for obstructions or plugging


If you want send me your email address and i will send the whole trouble shooting chart. If sent as an email it will have the structure needed to follow the steps it ask's you to do , if i post it here it gets all jumbled up.

Sharkey

iTrader: (1)

i do have access to alldata at work and the factory service manuals, ive ran through the troubleshooting chart and didnt come up with a solution (i consider that to be the basics). 99% of the time when i diagnose codes based on the gm charts i find the solution, but my own car has to be the PITA.

i did have a thought but its far fetched. according to the diagnostics, bad fuel can cause this code. the first time it was set was the day after i filled up with fuel. when the code set again it was the day after i filled up with fuel, however id run 2 tanks in between and i fill up at the same station. if i dont have this solved by the time the tank is empty ill fill up else were next time.

i think whats got me confused the most about this is that its setting the code on coast down were the pcm cuts fuel to assist with engine braking and help with economy (decel fuel cut). the pcm is commanding a very short pulse width during decel.

Sharkey

iTrader: (1)

bump, anyone have any thoughts???

Sharkey

iTrader: (1)

ok so time for an update here.

i cleaned my maf 2 weeks ago and the same day i had to fill up with fuel, but i didnt fill up at my normal station. i went through 2 tanks of fuel from different petro canada stations with no issues. i filled up yesterday at chevron (what i normally put in as they always have 94) and it set the code about 20km later again. now i noticed when i was running petro canada fuel the fuel trims came way down, basicly were i would expect they would be. i wasnt wathing the fuel trims for the last few days as the problem seemed to be fixed, but im guessing they have climbed back up again.

anyone had this code caused by bad fuel???

Coblasts

Maybe it has something to do with the ethenol content in the fuel.
Otherwise you could try changing the O2 sensor just to see what happens.

What are you using to watch all this ,do you have a program(hptuner) for your laptop ?(just curious)

Sharkey

iTrader: (1)

im wathcin it day to day with my interceptor and i use the snap on solus scan tool at my shop.

funny thing is ive been running chevron fuel since i bought the car 2 years ago (i fill up at the same station every week) as they are one of the only stations close by with 94.

outtamymind

petro doesn't have ethanol blended gas and did you check yoru intake piping as you said you had modded a CAI to your stock box, for any leaks or rub throughs. also when was the last time you changed your fuel filter if you haven't already. i had the same issues for the longest time with my 2.4 but mine turned out to be with my CAI and ported exhaust manifold the car didn't like the stock gap and would keep my LTFT's at around 17-19%, changed my plug gap a little bit and bam everything was great again.

Sharkey

iTrader: (1)

intake piping is all good, fuel filter is 5k old, plug gap is .035 (bkr7e). neither petro canada or chevron use ethanol blended gas, and both are top tier gasoline (recomended fuel by gm, dodge, toyota and bmw).

i checked all the obvious stuff, cleaned the maf. the only thing that seems to change it is the fuel. guess the easy thing to do would be not to fill up their anymore.

rukkee

iTrader: (3)

Does it misfire at all? IS it possible you have a gummed up injector or one that isn't delivering the commanded fuel so its trying to add fuel with the trim's? Just thinking out loud .

Gene Culley

iTrader: (1)

If you're running a 2.9 on a Stage 2 then it is probably lean anyway. I know you say you've had it this way for a while, but it still may be tuned lean now.

adsugslo

Thanks 4 sharing,bros

Sharkey

iTrader: (1)

if you actualy read my first post you would see that according to gm (shop manuals) the code only sets between 15 and 100kpa (basicly anything 0psi and lower). also you would see that the freezeframe data showed the code being set under decel. that means the issue im having is NOT related to a 2.9 pulley. yes i know 2.9 and stage 2 isnt ideal, but thats nothing to do with this. your comment is invalid.

i have noticed every so often it will get a few misfire counts under decel, but not that much (usualy stays under 8, will go 2-4 at most on one hole). i guess gummed up injectors are an issue, although the car is under 100k km (60k miles) and it wouldnt really explain why it changes with different fuel.

rukkee

iTrader: (3)

No It wouldn't explain why it changes with different fuels Weird .

I just tore apart my buddies 05 SS/SC with 46K miles on it . When i took the injectors out they were plugged with rust and red silt . The fuel rail had hardened mounds of the crap at each injector plug-in and it was built up at each end of the rail . We ran the fuel pump with the line off the rail ....and it flushed out enough rust to cover the bottom of a small gas can. The fuel filter had been changed regularly and was done a couple weeks prior and he runs only good gas (93).

When we drove the car prior , it ran fine till 5K rpm then it would feel like it ran out of fuel , then it showed a misfire on number 2 ....but only above 5K. I wish i would have taken pictures .....I was amazed the car ran at all, It was that bad.

I have a theory that something in the fuel system is rusting from the inside on these cars . A lot of the rust and crap was big enough to get caught in a filter ..... hell even a screen would have filtered them out . I'm still wondering where it all came from.

Gene Culley

iTrader: (1)

I don't exactly think it is necessary to be ornary here. I read the service manual, and code can come on even with incorrect fuel trims. You also have a condition on the vehicle, 2.9 pulley, that can cause the code... so again.. get your car tuned properly for the pulley and then see if it comes on. Heck, if you still have the stage 2 pulley, then put it on and see what happens.

Sharkey

iTrader: (1)

ok here is why i say the pulley wont cause the code. here is the info right off alldata, and it matches word for word the gm shop manuals

if any of the conditions are not met it will not run the diagnostics to run that code. the code isnt caused by incorrect fuel trims (the way thats worded makes it sound like its something you can adjust), its caused by the fuel trims climbing too high, indicating that the motor is running lean. and also, if you had read my original post you would see that the freeze frame data (thats the data list exactly when the code was set) shows the car wasnt under boost, in fact it was under decel (around 30kpa iirc), also showing that its not because of the pulley. add to the fact i can go a couple days without stepping on the car (mabey seeing 5psi max) and it has still set the code. as i said, i know a 2.9/stage 2 isnt ideal, but the information shows its not the problem.

Gene Culley

iTrader: (1)

The fuel trims will cause the P0171 to come on. Why? I'm currently experiencing it myself. System is running lean, so the system is trying to compensate for it, high fuel trims, and then it sets the code. I have data logs to prove this on my end as well.

I've read your posts dude, from start to finish. Stop trying to insult me and get your car tuned for the correct pulley.

Sharkey

iTrader: (1)

im not trying to insult you, but i dont think you fully understand whats going on with this. you do know tuning a car that has a legitimate mechanical problem is opening up a can of worms in itself, right??? if i was to have my car tuned now and i eventualy find the problem the tune is going to be out to lunch. tuning it at this point would be like me telling a customer with some mods on his truck that he has to tune the transmission to match the engine performance and that will fix the mechanical problem in his transmission.

i see you have a g5, is it boosted??? if not, its a completly different animal as far as this code goes. ill repeat again that the code is only monitered out of boost in most obd II cars, in a non boosted car it will be monitered anytime your not in PE mode. with a boosted car, anytime you cross above 0psi the pcm no longer moniters the fuel trims to set this code. the fuel trims may be very high, above 18%, but it wont set the code because the pcm isnt monitering for that code.

im not new to drivability diagnostics, i am a transmission tech, i do my share of diagnostic work. however, i havent ever delt with this code (anytime my shop runs across it we send it to the general repair guys). i know how fuel trims work, when the codes will set,and ive followed all the diagnostics but its lead me to a dead end, as it sometimes does, and thats why i asked for help with the people who know cobalts best. i apologise if im comming off like a dick, i dont mean to, im just a little frustrated with this issue im having and when im told to do things that obviously wont fix the problem.



now another update to my problem, set the code 3 times today, all 3 times was under decel, twice exiting the freeway and once down a long hill. the entire day i have not gone into boost (heavy traffic today). the only fuel trim cells that are high are the ones under high vacuum. i didnt have the scan tool with me today but the fuel trim thats reading that highest is around 2600rpm under decel, around 24" vacuum (somewere around 30kpa) . the fuel trim there is at 19.8, the cell bellow that (rpm wise) falls to 13, and next down is 7, and during normal driving they are actualy pretty close to 0.

Gene Culley

iTrader: (1)

Listen, I was just trying to help. You're obviously thinking it is one thing and denying anything else that comes along because you don't believe it... but I wouldn't suggest asking for help if you're not open to what you're going to receive and by trying to insult people. I will not bother your thread again.

outtamymind

the one thing i've come to realize with these cars is that multiple differen't things that will cause the same symptom.

Gettinausernamesucks

Rukee
the red silt as you call it could be red algae. It is not uncommon for some fuel stations to have water in their fuel tanks especially older stations that have leaky fuel tank caps. Usually fuel stations keep a few thousand gallons of fuel to insure the pickup (its a surface float in some cases) stays out of any possible water contamination. Now that ethanol blends are making a comeback the ethanol pickups up the water because ethanol is hydroscopic. Along with the water it can pick up algae in the water in the station tank. Usually the fuel station pump filters will catch most of it but not always. Once you get what I call an infection in your cars fuel tank and if your running an ethanol blend it tends to grow like a disease. red algae is quite small and can pass the filter and settle in the fuel system.

Algae growth in diesel fuel is very common.

Then again it could be rust LOL

Sharkey

iTrader: (1)

im not trying to deny help, but you obviously arent looking at the info in the gm manual pertaining to this code. i know its not caused by the pulley, if it was why would it set 3 times in one day if when i never went into boost???

outtamymind

you say its on decel that it only happens well i would start double checking your vacuum lines for any leaks as i know this can cause the code to pop up. how is your valve cover breather hose, is that connected correctly and not leaking