Irratic mpg?

Discussion in 'Motorhome Chat' started by pij974, Aug 29, 2010.

  1. pij974

    pij974 Funster

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    Hi all :thumb: We have a tag axle motorhome 2.8 jtd 2007 (old shape) which has been chipped. We use the van mostly on long motorway runs, so you would think conditions are quite similar but I get quite different mpg figures, between 13 and 27 mpg, all be it the 13 mpg was through the depths of devon on twisty twiney roads and steep inclines. Usually it wont go below 19 on motorways but can be as high as 27. I would of expected it to do 27 mpg on motorway runs, do you think something is playing up like an air flow meter or am I barking up the wrong tree?
    Thanks in advance
    Paul
     
  2. pappajohn

    pappajohn Funster Life Member

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    are you relying on a fuel/trip computer or actual liters/miles used between top-ups?

    if its a trip computer i'd suspect a fault.
     
  3. andyman

    andyman Read Only Funster

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    I have just sold a Autotrail Apache. I never seen 27mpg. Keeping to 60 I got a 25.6. If you are hoping for 27mpg, better start pushing
     
  4. pij974

    pij974 Funster

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    Hi Pappajohn, I work it out at every fill up, no trip computer. What should I be expecting to get?
     
  5. pappajohn

    pappajohn Funster Life Member

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    my 2.8tdi pulling 3.85t will return 26mpg solo and 25mpg towing a corsa toad at around 50/60mph on assorted roads.

    this has been checked over maybe 8 tank fill-ups and i dont fill until almost empty....sometimes too close to empty :Doh:
     
  6. rainbow chasers

    rainbow chasers Read Only Funster

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    You will get better motorway miles as your momentum is regular. When touring the likes of devon and cornwall, or travelling the A30 you will fall rapidly through the floor, as each bend and hill is detrimental to your momentum.

    If you imagine that each of these requires the engine to pull the full weight, up a hill without the aid of its' momentum, not only does it make it slow and a crawl, but a very thirsty journey as most drivers plant their foot to the floor to get up the inclines - let her crawl up in her own time!

    To give you an example, we can get from exeter to norfolk on less than half a tank without issue (around 250 miles?) - it takes the SAME AMOUNT to get from exeter to mid cornwall - 70 miles!
     
  7. pappajohn

    pappajohn Funster Life Member

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    strange as it is, i got the same 25mpg average towing the toad on a 1000mile tour of scotland as i do on the motorways going to shows etc.
     
  8. niggle

    niggle Banned - Rule 1

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    :cry: had mine remaped by wow tuning now will do 29.3 mpg,,, did have one problem with poor fuel consuption,, they changed a valve on the exaust i think :thumb:
     
  9. pij974

    pij974 Funster

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    Ours has been re-mapped by wow. I wouldnt say it has bettered the economy, only that I need to calculate the average over a longer time, maybe a couple of thousand miles or so. One thing I did find strange is that when its started and on tick over, it smells like really heavy diesel fumes as if your trying to gas yourself in a garage with no doors open. Maybe I need to get the exhaust valves looked at?
     
  10. Reallyretired

    Reallyretired Funster

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    Just come back from the twisty hilly roads of Devon. I was only getting 35-40 mpg from the Smart toad, normally get around 70, so not surprised you were using a lot of fuel.
     
  11. rainbow chasers

    rainbow chasers Read Only Funster

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    This is the difficulty when people ask about mpg - it depends so much on the driver, the vehicle, the load on the vehicle, and even the trerrain - not just regards to inclines, but altitude as well. It really is a length of string question!

    To make it more awkward, some vehicles in practice, actually perform more efficiently loaded to the hilt. Even one of my old recovery wagons was like this - loaded wasn't to bad at all - empty it would drink like a jeremy kyle guest!:thumb:
     
  12. Wow

    Wow Trader - Engine ReMapping

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    MPG Problem

    Hi Paul,
    I dont think exhaust valves would have such a huge effect on fuel consumption,
    I have a remapped 2.8JTD and in hard driving to shows I see 26 but in holiday mode I often top 30, Ilive in Cornwall so we have a few hills.
    I suspect that your remap is simply overfueling on heavy throttle loads (hence the smell of unburnt fuel), its not an uncommon problem as many maps are done for delivery vans running medium to light loads rather than a heavy motorhomes.
    The weight is holding back the van and not allowing the engine to rev as freely as a lighter van, thus you're chucking fuel into the engine without benefit.
    Cheers,
    Chris
     
  13. Jaws

    Jaws Funster Life Member

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    Pug 2.8 pre facelift with a Miller 7 berth body. We had it chipped by Torquing of Cats

    Just back from a 3k+ mile trip so have had lots of time to play and get figures
    At 60ish we get 27.. at 70ish 24mpg, and the weird one..50mph 23.5 mpg !

    Now that odd ball figure may well be something related to your problem.. Perhaps the control is over fueling at lower revs ?
     
  14. acting_strange

    acting_strange

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    I hope I'm not treading on toes here but that 23.5 is normal....it's all about REVS over weight. Normally 55 to 65 is the given mph or 2500 to 3500 revs gives the best mpg. In truth the best way to get the best is to have a vacuum gauge fitted and drive by that:thumb: Vacuum is high at tick over etc and when the throttle is floored but in the range shown above it drops dramatically.

    hope this helps:thumb::thumb:
     
  15. Jaws

    Jaws Funster Life Member

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    No toes trod on here and yes, as a life long mechanic I would agree, however, before I fitted the injector over write control I got 22mpg at 50mph and 19 at 60mph
    Cannot remember the revs at 60 but as it tops out around 95mph and red lines at about 5ish I reckon your right on the money :Laughing:

    Torque is a wonderful thing !
     
  16. Wow

    Wow Trader - Engine ReMapping

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    Hi Paul,
    Sorry didn't realise we had done you van:Doh:
    I will be happy to look at it free of charge for you and make any adjustment necessary, or if there is no adjustment to the map needed, then our diagnostic equipment might point you in the right direction. Are you going to Shepton Mallet or Lincoln as we can look at it there for you, if not give me a call and I can arrange something.:thumb:
    Cheers,
    Chris

     
    Last edited: Sep 9, 2010
  17. Wow

    Wow Trader - Engine ReMapping

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    'Chipping' Explained

    Hi Jaws,
    Your results wont relate to what Paul has got, his can be fixed quite simply. :thumb:
    To explain why. Your vehcile isn't 'chipped' as such, its fitted with a tuning box that sits across the common rail sensor and tells the ECU to increase fuel rail pressure.
    Chipping is when the ECU is physically removed from the 'van, the main control chip removed and reprogrammed and then refitted. Remapping is exactly the same as chipping, except that the reprogramming is completed via the diagnostic socket. Remapping is done in the case of 99%+ of post 2001 vehicles.
    Tuning boxes, unlike remapping, doesnt control torque maps, throttle maps, turbo pressure, torque limits, etc, but they do produce good power which is as everyone knows is sorely needed in the 2.8JTD, particularly with the high ratio top gear.
    A JTD at only 50mph should sip fuel, mine is well in the 30's when I do. If your box has an adjustment wheel, you could try backing it down a click and see if it helps your low speed speed fuel and hopefully without any real detriment to performance... Or you could do 60 everywhere!!:Rofl1:
    Cheers,
    Chris

     
    Last edited: Sep 9, 2010
  18. Jaws

    Jaws Funster Life Member

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    Box has three adjustments.. and the motor is not a JTD sadly ( or so I am told.. and there are certainly no JTD badges on it, only the old Boxer ones ).. It is a 03 to 06 model that was registered in 07 ( handy in one way as the loom wiring is not CANbus so no mucking around with relay interfaces etc ! LOL !)
     
  19. Wow

    Wow Trader - Engine ReMapping

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    The Boxer doesn't have the badge (Fiat only), but i'm pretty sure you will still have the JTD engine. Worth trying another setting on your though as you seem to have a very strong fuel supply there getting more MPG at 60mph??, if it was a remap with that sort of result we would reduce the fueling.

     
  20. Jaws

    Jaws Funster Life Member

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    Cheers for the info.. Might well come and speak to you at Lincoln and end up doing a deal if you reckon we could do better than 27mpg at 60 ?
    Just spent about £650 in diesel in three weeks so any improvements are always welcome and we will get our dosh back over the coming years without doubt !
    Even the set up we have at present, fitted middle of last year, has £450+... about 90 gallons, in diesel so well worth it !

    just over 10k miles done
    10k at 21mpg ( average ) = 476 gallons = ( about ) £2380

    10k at 26mpg ( average ) = 384 gallons = ( about ) £1923

    Cost of unit £230.00 over all saving in one year £227.00 A sum not to be sniffed at

    And all this from someone who really did think the whole tuning for economy thing was a load of old squit ! :Rofl1:
     
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