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Currently on a long interstate driving vacation. Twice during first 1000 miles I had a cel at high elevations (7000ft, 4000ft) with codes P0171 and P0174 (lean bank 1 and 2). These codes appear when the long term fueI trims hit 25 percent.
Followed advice to have fuel pump pressure checked and its fine at 62psi. Now im faced with figuring out whether I have an air leak or bad sensor somewhere.
Need to know what sensors to log using my obd2 to determine if MAF or any O2 sensors are bad. I assume that that throttle percent, rpm, are good data... but are there others, and what conditions should I log at?
Car is stock apart from Borla ATAK pipe. Runs really well, the codes were a surprise. Advice appreciated..!
If you can data log some way watch short term fuel and spray carb solvent (highly combustible be careful) around the intake area downstream of the Maf, this will respond instantly clearly showing the leak. Propane can be used as well if you are concerned about spraying liquid on your engine. If no leaks are found suspect Maf. If you want the ultimate in testing find a competent driveability shop and request a smoke test. This involves sealing the exhaust, Maf inlet and injecting low pressure( 26"H2O /less than 1 psi)smoke into the manifold.
honestly id pull the plugs and see if its running lean or rich. if its rich, o2s are bad. if its lean, MAF/intake leak.
Mafs (card type) are like $30 so you mght want to just swap it just to see... As far as intake leak... could be anywhere. Check the coupler, any lines going to it, and i believe behind the valve covers there will be the pcv return going to the intake. Possibly check your intake manifold for cracks as well.
If you can data log some way watch short term fuel and spray carb solvent (highly combustible be careful) around the intake area downstream of the Maf, this will respond instantly clearly showing the leak. Propane can be used as well if you are concerned about spraying liquid on your engine. If no leaks are found suspect Maf. If you want the ultimate in testing find a competent driveability shop and request a smoke test. This involves sealing the exhaust, Maf inlet and injecting low pressure( 26"H2O /less than 1 psi)smoke into the manifold.
I'm home; got another CEL today, about 1500 miles after the last one. I also ran my OBD2 to watch the fuel, MAF and throttle readings for last hundred miles. At idle, the LTFTs are at or close to 0, so it dont think its a vacuum leak. When cruising at 60-70, they are in the + teens, with bank 1 always about 3-5% above bank 2 - that might be a clue.
How big a hole/ gap am I looking for in the intake? The plug for the evap vent into the flexible coupling had a smear of oil/dirt next to the hole which might be evidence of a leak, but is it possible for enough air to leak in around the evap vent plug to cause trims to rise by over 10%?
I haven't tried the propane yet (will get a torch) but will probably start by pulling off the intake and making sure it's all put together right.
If idle trims are zero then vacuum leaks are almost certainly not the problem as they are most noticeable with the throttle closed. How is your wot power? A skewed maf could cause this. Bank to bank irregularities are not uncommon even with everything working. Can you check f/p while cruising? If you suspect lazy o2 swap the primaries and see if the bnk to bnk % reverses. Monitor IAT and see if it reflects ambient temp on start up and reasonable increases during cruise.
If idle trims are zero then vacuum leaks are almost certainly not the problem as they are most noticeable with the throttle closed. How is your wot power? A skewed maf could cause this. Bank to bank irregularities are not uncommon even with everything working. Can you check f/p while cruising? If you suspect lazy o2 swap the primaries and see if the bnk to bnk % reverses. Monitor IAT and see if it reflects ambient temp on start up and reasonable increases during cruise.
A quick check of IAT on start shows an IAT of 72-75 degrees and it's 65 in my garage. Is that ok or not ok?
by any chance do you run a K&N filter? I know when they're over oiled they can cause issues with MAF heated wires... Do you have the card style MAF (08+) and not the tube style (05-07)? If its the card style, I'd pull the maf (two torx bolts) and see if the exposed wire looks dirty/oily.
I just squirted propane in every place I could think of while watching the STFTs and got no reaction anywhere unless I squirted it up the intake. None of the PCV, EVAP, etc hoses are loose.
Originally Posted by Ahrmike
by any chance do you run a K&N filter? I know when they're over oiled they can cause issues with MAF heated wires... Do you have the card style MAF (08+) and not the tube style (05-07)? If its the card style, I'd pull the maf (two torx bolts) and see if the exposed wire looks dirty/oily.
Your IAT values are acceptable, drive and monitor. Also the question posed about the K&N is very relevant. Your leak test sounds very thorough, I don't believe your issue is vacuum leak related, idle f/t supports this as well. MAF becoming very suspect. I assume you have zero exhaust leaks pre upstream O2.
Your IAT values are acceptable, drive and monitor. Also the question posed about the K&N is very relevant. Your leak test sounds very thorough, I don't believe your issue is vacuum leak related, idle f/t supports this as well. MAF becoming very suspect. I assume you have zero exhaust leaks pre upstream O2.
The air filter is stock and only 4000 miles old. I plan to remove the intake tonight to check for upper radiator baffle leaks per this TB*. I will also clean the MAF using the spray recommended. I don't have a lift so once the intake side checks out I will have to go get help to work the exhaust side. I have run scans of the 4 O2 sensors but I cant tell if what they are doing is kosher. Is there a guide anywhere on how to test O2 sensors using a scan tool while driving?
The only other thing that is starting to worry me is whether someone has tuned this car (badly) before. I doubt it, but do I need a Tech2 to see whether the tune is stock?
*#08-06-04-040: Malfunction Indicator Lamp (MIL) - Check Engine Light On, DTCs P0171 and/or P0174 Set (Perform Repair As Outlined) - (Aug 13, 2008)
New MAF is coming Thursday. Until then, I got into TorquePro and finally managed to log some data driving around my neighborhood to see if anything leapt out. I hope you'll find the results interesting.
All 5 images show different sensors over exact same timeframe - about 9 minutes: up a hill, along, down a hill, then up a short hill home. I gave it some power up the long hill and was off gas for the long downhill (and I changed up to 6th).
First image shows the MAF, throttle, and rpm: note the long off-gas period going downhill from 47:36 to 48:00
Second image shows the STFT which (to my inexperienced eye) seem fine until they floor at same timeframe then rise way, way up.
Third image is the LTFT which show bank 1 seems to have a permanent 3% bias above bank 2, but in the timeframe of interest they rise way up trying to trim out the STFT
Fourth image shows what I think is a normal plot for the upstream O2 sensors 1 and 2 - but is it normal for them to go to zero in that period of interest, when going downhill in high gear off gas?
Fifth image shows the downstream O2 - they seem to be in sync pretty well but on a few occasions bank 1 leads or reacts faster than bank 2
Would welcome your comments and diagnosis. Sorry for the large images.
I had some LTFT issues after my headers went in recently... I ended up with a code for one o2 sensor having heater issues but the other being fine. I swapped both anyway and my LTFT issues were gone soon after. I think the lag time of the moved location + o2 sensors getting old were creating most of my issues. You may want to swap both primaries ($100 from amazon for both) just as a precaution. My car only had 30K+/- miles on it but it was 7 yrs old so i guess it was nearing its end of life.
I had some LTFT issues after my headers went in recently... I ended up with a code for one o2 sensor having heater issues but the other being fine. I swapped both anyway and my LTFT issues were gone soon after. I think the lag time of the moved location + o2 sensors getting old were creating most of my issues. You may want to swap both primaries ($100 from amazon for both) just as a precaution. My car only had 30K+/- miles on it but it was 7 yrs old so i guess it was nearing its end of life.
Understood, but before I swap out more than the MAF I'm hoping an experienced tuner in here will look at those plots above and help me rule out at least some of the sensors as the cause of the problem. I just cant figure out why the STFTs and LTFTs soar from 47:36 on.
Off the gas above 1400 rpm or so the PCM turns off the injectors thus the the zero output during decel. This is done to conserve fuel and lower pollutants. Your O2 sensors seem to be doing well. Remember that your datalog is not exactly real time due to the enormous data collected, compared, and displayed so some events may not be fully in sync.
Off the gas above 1400 rpm or so the PCM turns off the injectors thus the the zero output during decel. This is done to conserve fuel and lower pollutants. Your O2 sensors seem to be doing well. Remember that your datalog is not exactly real time due to the enormous data collected, compared, and displayed so some events may not be fully in sync.
That's very useful info. It looks like the problem initially arises when the rpm then falls enough for the injectors to turn back on - both ST and LT fuel trims go through the roof, and stay there apart from those periods where the injectors are again shut off.
Any idea why the trims would spike when the injectors come back on?
After hours of searching it sounds very similar to THIS so I will check and fix the close-out panel and holes in frame plate next to the intake per the TSB and see
Well a new MAF has gone in, and in the first test drive the LTFTs didnt go over +9, which is a first. Will log for a few more days before I declare success.
One new, strange thing I noticed from all my logs so far is that on full throttle, both Absolute Throttle and Throttle Position (Manifold) PIDs max out at 88.4 %... not 100% ....even with revs going above 5000 on acceleration. What is up with that?
Well a new MAF has gone in, and in the first test drive the LTFTs didnt go over +9, which is a first. Will log for a few more days before I declare success.
One new, strange thing I noticed from all my logs so far is that on full throttle, both Absolute Throttle and Throttle Position (Manifold) PIDs max out at 88.4 %... not 100% ....even with revs going above 5000 on acceleration. What is up with that?
Dont quote me on this but I believe its a GM failsafe. normally when sensors fail, they go full open or closed (100% or 0%) by forcing "max" to be less than 100, if it hits 100 they know the TPS is bad. The "commanded TPS" is a better one to datalog - it will go to 100%.
04-07-2018, 12:31 AM
Help Diagnose High LTFT Problem P0171 P0174
