Fuel trim readings got me chasin my tail
06-03-2018, 08:20 PM
#11
Again, what condition is the air filter in? If you changed it did you put it in the housing with the plastic bullet facing away from the engine?
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06-03-2018, 08:29 PM
#12
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Not to jump in on too far on Steve83's advice, but the "trim": numbers are really just directly related to how long the injectors are staying open in order to make the O2 senor readings correct. The PCM or ECM or EEC, the computer, just adds more injector open time until the O2 sensor says it's close to stoichiometric. The + or - is based on what "should" happen, more injector open time or less time, based on the engineer's original map for a perfect engine. So, high trim numbers mean either that there's an air leak after the MAF sensor, or that not as much fuel is squirting as should be when the injectors are open.
Your post is confusing because you have the -- in front of some numbers. Is that supposed to be a negative sign? Why are there two negative signs? You said that you're getting lean codes, which fits the high "under load" numbers. Do you have Freeze Frame data? You have to pull it from the PCM using your OBD scanner.
It is possible to get negative trims. Oil burning would look like fuel to the O2 sensors.
Your post is confusing because you have the -- in front of some numbers. Is that supposed to be a negative sign? Why are there two negative signs? You said that you're getting lean codes, which fits the high "under load" numbers. Do you have Freeze Frame data? You have to pull it from the PCM using your OBD scanner.
It is possible to get negative trims. Oil burning would look like fuel to the O2 sensors.
intresting point about the oil burning cause just in the last week i started hearing a slight kind of top end knock that only lasts maybe a minute at startup and twice now ive noticed a slight puff of blue at startup. I'm wondering now if i have valve guide issues or something.
06-03-2018, 08:55 PM
#13
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Rnlcomp's point is a good one, about the air filter. Air flow turbulence. Basically, turbulence at the MAF sensor can cause problems. The MAF sensor needs smooth laminar flow. You don't have a funky CAI setup do you? Dirty MAF sensor?
06-04-2018, 12:28 AM
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06-04-2018, 12:42 AM
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No CAI setup its all barebones stock (no pun intended). MAF was cleaned with gunk mass air flow spray cleaner and seems to be working fine. What i mean by that is the g/s increases as rpm increases but im not sure if there's a specific number it should read and i dont have baro on my obd display
06-04-2018, 01:04 AM
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06-09-2018, 10:59 AM
#17
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Not according to Ford, and not according to goinwheelin. They only have him chasing his tail.Only AFTER following the book precisely, and you're sure it doesn't work.Laminar flow is a myth from the 60s. You'll never find it anywhere near a car, and the MAF certainly doesn't require it....except the fault codes.
Yes, it's hyper-specific. But you can't know what it is without knowing the exact airflow at each moment (somewhere around 200x per second). But you CAN look for it to be relatively steady at a steady RPM. Check at SEVERAL steady RPMs.It's not a list - it's a logical process. Start at the beginning, and do what it says. If it says to skip 10 steps, DON'T do those 10 steps.
06-09-2018, 10:17 PM
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Imo , if you have lean codes, you got a vacuum leak , probably the pcv elbow or the intake boot , your getting unmetered air into the engine , unless you have exhaust leaks before the o2s .
if the mass or fuel pressure was messed up , you wouldn't have any power , it would not want to accelerate .
if the mass or fuel pressure was messed up , you wouldn't have any power , it would not want to accelerate .
06-09-2018, 10:43 PM
#19
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If the MAFS elements, the wires, are in a dead zone (like an eddy in a river of air) then they won't be showing the ECM how much air is actually entering the engine. "Laminar" in my example just means that the MAFS elements see the same air velocity as the total cross section of the intake tube. One "layer" of air is the same as any other layer. That the MAFS reading represents the total air flow. If you have higher or lower flow across the MAFS wires the ECM will not have the information it needs, and will not control the engine correctly.
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F150Torqued (06-10-2018)
06-10-2018, 10:12 AM
#20
LightningRod
Lean code come SOLELY from a very ridged bit of binary logic in the PCM. (LTFT > 25% -AND- STFT >5%). Logical meaning - Positive Fuel trim is being added (lengthening injector pulse width) exceeding factory fixed limit. (O2 sensor "VOLTAGE" readings have been trending to low). Another way of saying it, the PCM has reached its factory LIMIT of adjustment (trying to keep fuel/air ratio proper for it to run RIGHT). Up to this point, power should NOT have been effected, so that would be an improper, snap decision conclusion.
o- If injectors are dirty and delivering less fuel per given pulse width - this same thing will happen.
o- If fuel rail pressure is low (because of faulty FRP sensor, faulty FPDM or Fuel Pump) - this same thing will happen. Injectors are calibrated to deliver exact amount of fuel / at a certain pressure across them / during a specified period.
o- Random Misfires (from ALL their various causes) - will cause this to happen. Dumping unburned oxygen into the exhaust.
o- Low 'bias' voltage on O2 sensors will cause this. Altering the proper calibration of the O2 sensor output voltage.
o- Cross currents around MAF sensor as @BareBonesXL points out will cause this. (Common from moving MAF on aftermarket CAI additions)
o- Valve Cover gasket or Oil Pan gasket leak (which is technically a vacuum leak) will cause this.
My point - is; this, like so many diagnosis require a look at other things to get the problem in prospective before diving in with a snap diagnosis.
Last edited by F150Torqued; 06-10-2018 at 10:16 AM.