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MAF sensor and O2 sensor bad?

Discussion in 'LR4' started by Michael Gain, Feb 23, 2021.

  1. jlglr4

    jlglr4 Full Access Member

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    I didn’t think of the manifold leaks. I believe that could cause a lean condition if it’s drawing some air in rather than spitting it out - maybe changing with throttle as you’re seeing. I need to check this as well - my fuel trims are also running a little high, around 7% or so, but not causing any other symptoms yet. I think I recall you and Fuji4 both have had exhaust manifold bolts that snapped off. What’s the best way to get a look at that part of the exhaust manifold.
     
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  2. Michael Gain

    Michael Gain Full Access Member

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    There is no good way, brother. Send me a PM with your email and I'll send you the step-by-step.

    Basically:
    - remove tire
    - remove splash shields
    - remove heat shields behind upper control arm
    - remove one maybe two of the exhaust manifold heat shield bolts
    - remove under engine skid plate
    Option 1: try to contort your arm enough to reach past cat and remove the last heat shield bolt
    Option 2: remove cat to remove last bolt (passenger side cat will need a new exhaust gasket)

    - slide exhaust manifold heat shield out / move around to inspect the bolts

    For manifold gasket replacement:

    Both sides:

    -support engine and remove engine mount bracket (I also bought engine mounts to replace while I'm in there)

    Drive side:
    - remove ps pump
    - loosen and move a.c. compressor to the side
    - remove lower steering shaft (need new bolts for installation)

    Finally: unplug o2 sensor, unbolt exhaust manifold (noting position of bolt spacers) and remove.
     
  3. jlglr4

    jlglr4 Full Access Member

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    Good lord. I might wait until it starts showing more symptoms...or I get just extremely bored. But thanks for the info.
     
  4. DaytonaRS7

    DaytonaRS7 Full Access Member

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    my recommendation for the bg44k was due to your fuel trims. since you replaced injectors, id say its not necessary. but...it cant hurt. its actually part of the annual maintenance schedule. maybe itll clean other parts of the fuel system?
     
  5. DaytonaRS7

    DaytonaRS7 Full Access Member

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    this is somthign that's bothered me and I cant figure out any reason for. the fact that there are 2 MAF sensors that lead into 1 throttle body. whats the point? they should have put 1 MAF sensor directly in front of the throttle body. whether air comes from each side equal or not, all that matters is the total airflow into the engine.

    dumb design.
     
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  6. DaytonaRS7

    DaytonaRS7 Full Access Member

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    id agree. vaccum leak and most likely faulty MAF.

    your idle conditions are the only thing thats alarming.

    under load and coasting, the fuel trims seems to be behaving correctly.
     
  7. Michael Gain

    Michael Gain Full Access Member

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    I think I have a can floating around lol. FCP EURO had the MAFs for less than $100 and carry the fuel filter and gasket that others have reported leaking on top of the fuel tank. I ended up getting both MAFs and the fuel tank parts.
     
  8. Michael Gain

    Michael Gain Full Access Member

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    Coasting is where the faulty MAF acts up, but agreed that idle is my issue. My last smoke test showed no leak. I tested the vacuum lines and pushed smoke through the intake system.

    That said, last time I was playing around, I noticed the hard pipe from driver side valve cover seems a little loose where it terminates in the intake baffle. I plan on replacing it's o-ring, but also re-smoking the system. I have a feeling that if I do have a vacuum leak, it is there. Or, the brake booster line is leaking.

    There is no effect to braking, but the line is slightly elevated due to the new battery install:
    20201208_143316.jpg
     
  9. Michael Gain

    Michael Gain Full Access Member

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    Replaced both MAF sensors today. I also pulled out the driver and passenger pcv breather lines and put new o-rings on them. Upon reassembly, I made damn sure that they were seated and that the top and bottom parts of the collar clip clipped into place.

    I cleared the DTCs (will post more about that in my traxide install thread later) and started it up.

    Upon start up, I let it idle and then logged the live view numbers again (sorry, no screen shots).

    MAF flow values about pretty equal.

    Since I did not reset adaptations, LTFTs are ~6% on bank 1 and ~5% on bank 2.

    For the win, STFTs are about -4% for each bank. This brings the total fuel trims to +2% on bank 1 and +1% on bank 2.

    I can live with these numbers. If I see anything weird on my commute tomorrow, I'll report back.
     
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  10. Michael Gain

    Michael Gain Full Access Member

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    Well, idle bog when coming to a stop is still there (idle drops to 500-600rpm and the truck shakes until throttle is reapplied). Seems more pronounced when on flat ground than on an incline (nose elevated).

    Commanded fuel is higher than supplied fuel, but STFTs and LTFTs look good.

    The trouble shooting continues. I already have the low pressure fuel pump inbound. I was going to affect the fuel filter swap this weekend (preemptively) and figured that I would replace the pump while I had the tank dropped.

    Side note: while replacing the PCV o-rings, the oil smelled burnt to me. I did an oil and filter change Tuesday night and the mity VAC pumped out OVER 8L (I maxed the pump's capacity, had to dump some, and then continue pumping). Based on the overage since my last oil change, I am guessing that I have a little crankcase dilution from the misfire debacle.

    I did an oil change at 67K, before the injectors needed replacement. By 69K the oil was black and burnt. It did not smell like gasoline to me, but my sense of smell isn't what it used to be.

    Hindsight, I should have changed the oil when I swapped the injectors.

    That said, no unusual smoke and not burning oil. So, I think the rings are good.

    If it's not one thing, it's another with this truck... but I do love her though.
     

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