5.0 poor mileage and idle hunt/fluctuation
  1. Welcome to RangeRovers.net – General discussion forum for Range Rovers

    Welcome to RangeRovers.net - a website dedicated to all things Range Rovers.

    You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, Join RangeRovers.net today!
     
+ Reply to Thread
Page 1 of 4 1 2 3 4 LastLast
Results 1 to 15 of 51

Thread: 5.0 poor mileage and idle hunt/fluctuation

  1. #1
    FRESHMAN ROVER
    Join Date
    November 17th, 2015
    Location
    Huntington Beach, CA
    Posts
    107

    5.0 poor mileage and idle hunt/fluctuation

    For a long time now, I have not been able to figure out this issue. I used to get pretty decent mileage, averaging about 16MGP. Now I get 10-11, and something is clearly wrong, but no real codes. I have a bad cat, constant P0420, which is probably due to a bad tune on that bank, related possibly to this issue. The RPMs under constant steady load say on freeway fluctuates 100-150 RPM, and the instant mileage readout bounces all around. I heard of similar issues with the torque converter lock up going bad, but that is much more pronounced.

    Any guidance appreciated..

    https://youtu.be/VbYxP-r4i30

  2. Remove Advertisements
    Range Rovers Forum
    Advertisements
     

  3. #2
    FRESHMAN ROVER
    Join Date
    October 2nd, 2013
    Location
    Grapevine TX
    Posts
    194

    Re: 5.0 poor mileage and idle hunt/fluctuation

    How many miles on your car?

    Rob

  4. #3
    FRESHMAN ROVER
    Join Date
    February 25th, 2018
    Location
    Charleston, South Carolina U.S.A.
    Posts
    98

    Re: 5.0 poor mileage and idle hunt/fluctuation

    Would not hurt to boroscope your intake runners, check for excessive carbon buildup.
    2011 Range Rover HSE (Santorini Black, Jet Leather/Interior, Ivory Headlining)
    Charleston, South Carolina U.S.A.

  5. Remove Advertisements
    Range Rovers Forum
    Advertisements
     

  6. #4
    FRESHMAN ROVER
    Join Date
    November 17th, 2015
    Location
    Huntington Beach, CA
    Posts
    107

    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by anvilrob View Post
    How many miles on your car?

    Rob
    130k. at around 100k, I had full timing chain guide/chains, and practically any other part that was came off replaced, all new injectors, rebuilt supercharger snout, everything.. except for these variators, unfortuantely. Performed flawlessly for a while.

  7. #5
    FRESHMAN ROVER
    Join Date
    November 17th, 2015
    Location
    Huntington Beach, CA
    Posts
    107

    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by doc5339 View Post
    Would not hurt to boroscope your intake runners, check for excessive carbon buildup.
    Been thinking that as well, but the blower has to come off I believe to do this.

  8. #6
    FRESHMAN ROVER
    Join Date
    February 25th, 2018
    Location
    Charleston, South Carolina U.S.A.
    Posts
    98

    Re: 5.0 poor mileage and idle hunt/fluctuation

    Might be worth pulling the supercharger and taking a peep, and be ready to turn the crank and clean the valves chemically or walnut shell blast.
    2011 Range Rover HSE (Santorini Black, Jet Leather/Interior, Ivory Headlining)
    Charleston, South Carolina U.S.A.

  9. #7
    FRESHMAN ROVER
    Join Date
    October 2nd, 2013
    Location
    Grapevine TX
    Posts
    194

    Re: 5.0 poor mileage and idle hunt/fluctuation

    With that mileage it'd be worth doing a cylinder leak down test to determine the efficiency of each cylinder.

    In all likelihood, and a common issue with direct injection technology, it's possible you have a couple of less than perfectly sealing valves, especially at that mileage.

    The good news is that a head rebuild is relatively affordable vs an engine rebuild.

    Also, SDD allows many measurable parameters to be selected with the engine running.

    If you don't have access to that diagnostic equipment it may be worth spending an hour or two on JLR shop labor to more acutely diagnose the problem in advance of heading off down a potential rabbit trail.

    Lastly, is the transmission shifting correctly and are you getting "normal" RPM at highway speeds?

    Rob

  10. #8
    FRESHMAN ROVER
    Join Date
    October 2nd, 2013
    Location
    Grapevine TX
    Posts
    194

    Re: 5.0 poor mileage and idle hunt/fluctuation

    Meant to include this in the above post...

    VVT's can "stick" with advanced age and extended oil change intervals.

    If you do go the diagnostic route, this will be easily determined.

    Rob

  11. #9
    FRESHMAN ROVER
    Join Date
    November 17th, 2015
    Location
    Huntington Beach, CA
    Posts
    107

    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by anvilrob View Post
    Meant to include this in the above post...

    VVT's can "stick" with advanced age and extended oil change intervals.

    If you do go the diagnostic route, this will be easily determined.

    Rob
    Thanks for all of the info. One of the VVTs is definitely really noisy, and going to replace them next week (all 4). Will have him pull the intake again and inspect the intake valves. If a timing chain sprocket was off by a tooth, wouldnt it throw a code? I just want to make sure it wasnt an error when the chain was done 30k miles ago.

    Another symptom - I can hear light engine knock when motor is warm, under light accel/loads when in 5th/6th gear at RPMS under 2K.

    I really hope I can get this sorted out, as its already killed one 1300 dollar catalytic converter, and I dont want to put the next one in just to have it die too

  12. #10
    FRESHMAN ROVER
    Join Date
    June 5th, 2018
    Posts
    153

    Re: 5.0 poor mileage and idle hunt/fluctuation

    I see two potential issues: one is the bad cat code, which may be restricting exhaust. This will reduce mileage. The other is the trace knock at low rpm and heavy load. Though this could be due to the VVT, it could also indicate a timing or fuel issue. Either way, it may be an issue of ignition ping causing the ECM to retard timing due to the noise (knock sensor.)Valve timing could cause this, but so could a restricted exhaust. One cam tooth would likely cause a real driveability issue, not just noise. One thing to note here is the mileage being over 100K miles, which might indicate oil usage causing the ignition ping and the cat failures. Ray

  13. #11
    FRESHMAN ROVER
    Join Date
    September 29th, 2018
    Location
    long island, ny
    Posts
    233

    Re: 5.0 poor mileage and idle hunt/fluctuation

    Not sure if you have High pressure fuel pumps on that engine But if you do Check your engine oil level and smell inside the oil cap for fuel. If levels are high and or smell fuel than check for this.

    In some cases the high pressure fuel pumps can leak fuel into the engine oil and even throw the Cat code and even cause uneven rpms. Could also be the cause for the vvt being thrown out of wack. the reason for this is the fuel that is leaked into the oil when hot will cause vapor to recirculate back into the into manifold causing an imbalance.

    This of course is only if you have high pressure fuel pumps..
    2019 Range Rover Sport HSE Dynamic

  14. #12
    FRESHMAN ROVER
    Join Date
    January 30th, 2011
    Location
    Maryland
    Posts
    70

    Re: 5.0 poor mileage and idle hunt/fluctuation

    Quote Originally Posted by bill2019 View Post
    Not sure if you have High pressure fuel pumps on that engine But if you do Check your engine oil level and smell inside the oil cap for fuel. If levels are high and or smell fuel than check for this.

    In some cases the high pressure fuel pumps can leak fuel into the engine oil and even throw the Cat code and even cause uneven rpms. Could also be the cause for the vvt being thrown out of wack. the reason for this is the fuel that is leaked into the oil when hot will cause vapor to recirculate back into the into manifold causing an imbalance.

    This of course is only if you have high pressure fuel pumps..
    So some 5.0 engines have hi pressure pumps, and some do not?
    2012 Range Rover Autobiography
    91 BMW 850i 6 speed
    94 BMW 850 CSi 6speed
    Supercharged Tbirds x 3
    Audi S8 '03, '91 V8 Quattro 5speed

  15. #13
    FRESHMAN ROVER
    Join Date
    November 17th, 2015
    Location
    Huntington Beach, CA
    Posts
    107

    Re: 5.0 poor mileage and idle hunt/fluctuation

    I think any DI motor has to have a high pressure pump by design, so yes the 5.0s have one.

    Other observations - the throttle seems to hang a little after letting off the pedal for decel.. the MPG shows roughly the same as my cruise MPG. I used GAP tool and logged the TPS to look into it, and it does not fluctuate at all. stays put when i let off.. but it takes 2-4 seconds for the car to actually go into decel/fuel cut mode, and to feel more drag from the engine braking. It seems the hang is related to ignition timing/fueling. While doing this, I noticed there are two TPS sensors - "Absolute Throttle position" and "Absolute Throttle position B" - one was linear from about 13% at idle to 91% at WOT. the other one never got below 32% and was on average a much higher percentage, unless I got up to 50-60% then they would get closer to matching.

    Next, I have noticed that there is "Engine Coolant Temp" and "Engine Coolant Temp 2". does anyone know what these correspond to? the main one rose as normal with engine temp, leveled out to 87-89C. The Temp 2 stayed aroudn 10C then went up to 35C and stayed there after warming up. I know a bad coolant temp sensor can cause rich conditions.. but I don't know where this "temp 2" is pulling info from. I dont think it can be the outlet for the radiator, seems too cold still?

    Same basic thing with "intake air temp" and "intake air temp bank 2" - usually a 20C- 30C difference, which does not seem feasible if both bank are drawing from the same atmosphere..

    Lastly, LTFT for bank one is about -2 to -3%. Bank 2 is about -10 to -12%. Bank 1 has the dead cat. I swapped MAFS from left to right, nothing really changed for the fuel trims.

    I have basically been watching various parameters with the GAP tool, looking for anomalies that could lead to the diagnosis of this thing.

    If anyone has any other recommendations to watch/log/try, or knows what all of these "sensor 1 vs sensor 2" things correspond to, I am all ears. Next week it goes in for replacement of the VVTs, and hopefully further inspection/scoping of the intake valves.

  16. #14
    FRESHMAN ROVER
    Join Date
    September 29th, 2018
    Location
    long island, ny
    Posts
    233

    Re: 5.0 poor mileage and idle hunt/fluctuation

    Did you check the oil as i suggested? Many of the things you mention including the fuel trims and the hanging throttle are symptoms of this.

    The reason your fuel trims are so out of wack is the one side is trying to lean fuel, the very side that fuel vapors are entering the combustion chambers without passing through the throttle body they are entering the intake manifold on that side. the engine doesnt know this and is trying to balance this out by cut fuel delivery but it cannot control it.

    Dont over think it, the The two tps signals will not read the same one recieves half of the voltage as the other and they are designed to be averaged out by the computer, this is normal.

    The temp sensors are normal they monitor two different areas one on the hotter side the other on the cooler and return side. they are needed to monitor the vanes and coolant fan. this is normal.

    I strongly would suggest looking into the fuel pump issue before spending money on the vvt. the unbalanced fuel vapor load can cause the vvt problems. Remember if fuel is entering the cylinders at a time when no fuel is supposed to you will get combustion at the wrong time and will be very uneven there is only so much the ecu can do it cannot stop something it cannot see.
    2019 Range Rover Sport HSE Dynamic

  17. #15
    FRESHMAN ROVER
    Join Date
    September 29th, 2018
    Location
    long island, ny
    Posts
    233

    Re: 5.0 poor mileage and idle hunt/fluctuation

    I found this video to help you understand it a bit more. Perfect example of a faulty High pressure fuel pump and it possible symptoms. Found and fixed by a pro.
    https://www.youtube.com/watch?v=GlK-BZuq8K8
    2019 Range Rover Sport HSE Dynamic

+ Reply to Thread
Page 1 of 4 1 2 3 4 LastLast

Quick Reply Quick Reply

Register Now

Similar Threads

  1. 2006 Range Rover idle fluctuation
    By DougG in forum Range Rover Mark III / L322
    Replies: 4
    Last Post: November 29th, 2015, 05:08 AM
  2. Idle fluctuation on RRC with 3.5L EFI V8
    By Sensh in forum Range Rover Classic
    Replies: 3
    Last Post: November 24th, 2015, 03:11 PM
  3. CEL P0302 P0316 - Occasional Idle Hunt
    By NC-RoverMan in forum Range Rover Mark III / L322
    Replies: 9
    Last Post: February 15th, 2014, 07:46 PM
  4. 96 Rover: Very Poor Acceleration, Idles well - Poor Fuel Economy.
    By StrangeRVR in forum Range Rover Mark II / P38
    Replies: 1
    Last Post: December 4th, 2012, 11:52 PM
  5. Voltage fluctuation
    By kingkitesurf in forum Range Rover Mark II / P38
    Replies: 6
    Last Post: August 30th, 2007, 04:15 PM

Tags for this Thread

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Powered by vBadvanced CMPS v4.3.0