5.0 poor mileage and idle hunt/fluctuation - Page 3
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Thread: 5.0 poor mileage and idle hunt/fluctuation

  1. #31
    FRESHMAN ROVER
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by anvilrob View Post
    OK,

    Here's a printed out copy of the SDD screen results of the two depictions I was referring to (below).

    I was working on this normally aspirated MY2010 5.0 this past Saturday. Note, the car is running during both tests.

    The panel with the VVT displays zero misfire(s) while idling in the shop, yet the second more appropriate panel with just the misfire detection annotated data selected displays multiple misfires during a follow-on road test with an observer.

    Attachment 271894

    Attachment 271896

    If the shop you're using has SDD make sure they/you use the second/lower option and have TWO people on board, then take the vehicle for a test drive to monitor the data regarding possible misfire(s).

    One person drives, the other monitors the data from the passenger seat (unless you almost want to guarantee a wreck).

    The "Current column" is the number of misfires during THAT drive. The "Average column" is a cumulative detective record and although it may look less bold in the printout, the left side number is actually depicted in green on the computer.

    Before going any further, it's worth taking the time to do a compression check prior to spending any more money on parts - you need to make sure the motor is mechanically "well enough" as is.

    Good luck,

    Rob

    PS The first thing I did on this vehicle was check its normal operating temperature compressions (all good). No point trying to troubleshoot an external issue if the thing's worn out on the inside
    I agree - will have them rule out mechanical internal problems. Can you post larger versions of those photos? they are too small to read. or email if you can.

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  3. #32
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    Can you read oil temperature? About the only thing I can find that would inhibit the high lift cam profile switching is an oil temperature below 20C. I would assume the solenoids that activate the switchover, are monitored for shorts and opens by the ECU so there should be some kind of DTC if those were electrically bad.
    M Canning
    Massachusetts, USA
    2006 HSE Bonnati Grey/Charcoal Interior

  4. #33
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by Mrmerlin View Post
    Brav watch that video that Bill posted.
    Thanks for the info Bill.
    I did, and many others from Diagnose Dan! Great channel. No fuel in my oil however. Just did an oil change.

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  6. #34
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by MARK_C View Post
    Can you read oil temperature? About the only thing I can find that would inhibit the high lift cam profile switching is an oil temperature below 20C. I would assume the solenoids that activate the switchover, are monitored for shorts and opens by the ECU so there should be some kind of DTC if those were electrically bad.
    Yes, oil temp comes up. I did the test when everything was full hot (its around 75F in So Cal these days )

    It is strange, but maybe the parameter I selected was wrong? But I followed 2 parameters - one for the position, and one for the request, neither every moved away from the "low" setting even at WOT/Redline

  7. #35
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    Typically, when an issue is detected, the system will generate a "freeze frame," which will store all of the engine parameters at the time of the event. What I suspect here is an issue of ignition misfire, either due to coil packs dying, or leaking spark plug wires. What I typically see with engines with more that 50-60,000 miles on the clock and a misfire, is that the spark is leaking around the plug wires to ground, or the coil is arcing internally. There are several things causing off-idle misfire; one is that the mixture leans out off-idle. Yes, it stays at 14.7:1, but there are issues with effective compression, in other words, better cylinder filling off-idle, requiring more spark voltage to fire the plugs. The other thing causing higher effective compression is spark advance, which again raises effective compression. So does the cam timing, as it is creating EGR, which controls NOx. All of these conditions raise required voltage, and the resulting higher voltages can stress ignition components to the point of arcing. It is also possible for one or two plugs to have cracked insulators, causing arcing. If the codes indicate which cylinders are misfiring, you can use the codes to isolate the faulty components. Chances are that if one or two cylinders are the culprit, the others will soon follow. Ray

  8. #36
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by RABarrett View Post
    Typically, when an issue is detected, the system will generate a "freeze frame," which will store all of the engine parameters at the time of the event. What I suspect here is an issue of ignition misfire, either due to coil packs dying, or leaking spark plug wires. What I typically see with engines with more that 50-60,000 miles on the clock and a misfire, is that the spark is leaking around the plug wires to ground, or the coil is arcing internally. There are several things causing off-idle misfire; one is that the mixture leans out off-idle. Yes, it stays at 14.7:1, but there are issues with effective compression, in other words, better cylinder filling off-idle, requiring more spark voltage to fire the plugs. The other thing causing higher effective compression is spark advance, which again raises effective compression. So does the cam timing, as it is creating EGR, which controls NOx. All of these conditions raise required voltage, and the resulting higher voltages can stress ignition components to the point of arcing. It is also possible for one or two plugs to have cracked insulators, causing arcing. If the codes indicate which cylinders are misfiring, you can use the codes to isolate the faulty components. Chances are that if one or two cylinders are the culprit, the others will soon follow. Ray
    Thanks for the info. As it turns out.... the S/C engines DO NOT use cam profile changing (according to my LR tech). Just VVT. Also, HPFP test performed, everything working well, right on spec. I just wish these f-ing problems would be more apparent.

    I am not getting any misfire codes.. Just have tried to see if any are showing up. Plugs and Injectors are new, i think coils are original.. although I would think a bad coil would throw some kind of code.

    They are telling me that due to the bad CAT.. (P0420), the tune is being thrown off. I have a hard time believing that. He says the system is constantly pulling timing and enriching/leaning the mixture in order to determine if there is a misfire or other issue and develop another code.

  9. #37
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    One thing I noticed while perusing the previous pages was the apparent disagreement between TPS readings. Does this engine have two throttle bodies? Can you clarify the two TPS readings? I tend to agree with you re: the cat issue, but if one side is partially restricted, the resulting imbalance in the exhaust may cause the ECM to start "guessing" about what is going on. Let's start with the TPS issue. The Po420 code relates to the cat's ability to store O2. If the system is attempting to provide more O2 to that cat, it WILL lean that bank in an attempt to provide more O2 to that substrate. That makes more sense to me that the gibberish the tech handed you. Ray

  10. #38
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    The downstream O2 sensor connectors attach to mounting clips close enough to each other at the rear of the transmission that you could easily mark them and then "swap" them (the connector plugs) Left side rear O2 to Right side rear O2, and Right side rear O2 to Left side rear O2, and see if the "cat problem" compensation swaps sides too.

    What were the results of the compression test?

    Rob

  11. #39
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by RABarrett View Post
    One thing I noticed while perusing the previous pages was the apparent disagreement between TPS readings. Does this engine have two throttle bodies? Can you clarify the two TPS readings? I tend to agree with you re: the cat issue, but if one side is partially restricted, the resulting imbalance in the exhaust may cause the ECM to start "guessing" about what is going on. Let's start with the TPS issue. The Po420 code relates to the cat's ability to store O2. If the system is attempting to provide more O2 to that cat, it WILL lean that bank in an attempt to provide more O2 to that substrate. That makes more sense to me that the gibberish the tech handed you. Ray
    Only one TB. I think it has two sensors for redundancy/fault finding. The thing is, the P0420 is for Bank 1. The rich bank is bank 2. Ordering an OEM cat to finally eliminate the problem. Someone from GAP said they had a similar issue on a L322.

  12. #40
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by anvilrob View Post
    The downstream O2 sensor connectors attach to mounting clips close enough to each other at the rear of the transmission that you could easily mark them and then "swap" them (the connector plugs) Left side rear O2 to Right side rear O2, and Right side rear O2 to Left side rear O2, and see if the "cat problem" compensation swaps sides too.

    What were the results of the compression test?

    Rob
    Tests all came back good. Fuel pressure is spot on. Told me to get a new cat and recheck from there. Wish there was a better option vs 1300 bucks for one.

    While waiting for the cat., I am going to continue to monitor other parameters to see if I notice any more anomalies. I am getting 1-4 misfire counts every now and then on Cyls 2,4,6,8 (note, I am only monitoring that side, for misfires resulting in catalyst damage, and misfires resulting in emissions problems, 2 parameters per cyl, max 8 on IIDtool). Cyl 6 seems to be the most finicky, followed by 4 and 2. Misfires are mostly when at low RPM /Low load. WOT or high load shows zero. Will monitor bank 1 to see if there is a diff

  13. #41
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    hmm, I have the same misfires and rough idle for a year already... it all started after I replaced VVTI units and chains + all required parts (guides, tensioners etc)

  14. #42
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    Another useless update - replaced the bad cat, reset adaptations.. fuel trims went right back to how they were (negative on both banks) Surprise.. but at least no P0420 code anymore. the search continues.

  15. #43
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    In case I missed any previous reference to the injectors, have you replaced the injectors with new very recently or removed them, had their existing flows checked and or cleaned then re-tested and re-installed?

    Rob

  16. #44
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by anvilrob View Post
    In case I missed any previous reference to the injectors, have you replaced the injectors with new very recently or removed them, had their existing flows checked and or cleaned then re-tested and re-installed?

    Rob
    Yes, all are recently new, when I did the timing chain, guides, etc. Basically, anything that came off as a result of service or repair, has been replaced, with the exception of the coil packs.

  17. #45
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    Re: 5.0 poor mileage and idle hunt/fluctuation

    OK, are you certain that each injector was tamped down into its seat?

    They can't necessarily just be inserted by hand and then expect the fuel rail will "seat" the injector.

    If you have a "loose" injector you might get this type of issue.

    If you are absolutely certain you fully seated the injectors then disregard.

    If not, I'd consider removing the fuel rails and pulling the injectors, replacing their teflon seals and re-installing them correctly.

    It's also possible to have an occasional faulty injector although that's uncommon. A company in Houston called Injector RX is able to test and service DI injectors.

    Rob

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