Irratic mpg? (1 Viewer)

pij974

Free Member
Mar 17, 2008
65
7
Wellingborough, Northants
Funster No
1,854
MH
Low Profile
Exp
6
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
 

pappajohn

LIFE MEMBER
Aug 26, 2007
43,207
48,802
Dark side of the moon
Funster No
172
Exp
Since 2005
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.
 
Sep 23, 2007
1,702
1,966
Leicestershire
Funster No
347
MH
A Class
Exp
4 and many as a tugger
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

Subscribers  do not see these advertisements

 

pappajohn

LIFE MEMBER
Aug 26, 2007
43,207
48,802
Dark side of the moon
Funster No
172
Exp
Since 2005
Hi Pappajohn, I work it out at every fill up, no trip computer. What should I be expecting to get?

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:
 

rainbow chasers

Free Member
Oct 30, 2009
3,680
1,725
Mid Cornwall
Funster No
9,132
MH
Various
Exp
9
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!

Subscribers  do not see these advertisements

 

pappajohn

LIFE MEMBER
Aug 26, 2007
43,207
48,802
Dark side of the moon
Funster No
172
Exp
Since 2005
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!

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.
 

niggle

Banned - Rule 1
Banned
Aug 5, 2010
804
601
SOUTH AND FRANCE
Funster No
13,042
MH
A CLASS
Exp
30
: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:
 
OP
OP
pij974

pij974

Free Member
Mar 17, 2008
65
7
Wellingborough, Northants
Funster No
1,854
MH
Low Profile
Exp
6
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?

Subscribers  do not see these advertisements

 
Apr 27, 2008
11,794
13,952
Eastbourne East Sussex
Funster No
2,327
MH
Hymer low profile
Exp
Since 1972
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.
 

rainbow chasers

Free Member
Oct 30, 2009
3,680
1,725
Mid Cornwall
Funster No
9,132
MH
Various
Exp
9
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.


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:
 

Wow

Trader - Engine ReMapping
Sep 8, 2010
68
7
Charlestown, Cornwall
Funster No
13,611
MH
Coachbuilt
Exp
25
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

Subscribers  do not see these advertisements

 

Jaws

LIFE MEMBER
Sep 26, 2008
23,821
71,977
Thetford Norfolk
Funster No
4,189
MH
C class, Chieftain
Exp
since 2006 ( I think ! )
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 ?
 
May 16, 2010
3,213
2,535
North Hykeham
Funster No
11,622
MH
Custom
Exp
much more now
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 ?

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:
 

Jaws

LIFE MEMBER
Sep 26, 2008
23,821
71,977
Thetford Norfolk
Funster No
4,189
MH
C class, Chieftain
Exp
since 2006 ( I think ! )
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 :roflmto:

Torque is a wonderful thing !

Subscribers  do not see these advertisements

 

Wow

Trader - Engine ReMapping
Sep 8, 2010
68
7
Charlestown, Cornwall
Funster No
13,611
MH
Coachbuilt
Exp
25
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

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?
 
Last edited:

Wow

Trader - Engine ReMapping
Sep 8, 2010
68
7
Charlestown, Cornwall
Funster No
13,611
MH
Coachbuilt
Exp
25
'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!!:ROFLMAO:
Cheers,
Chris

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 ?
 
Last edited:

Jaws

LIFE MEMBER
Sep 26, 2008
23,821
71,977
Thetford Norfolk
Funster No
4,189
MH
C class, Chieftain
Exp
since 2006 ( I think ! )
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 !)

Subscribers  do not see these advertisements

 

Wow

Trader - Engine ReMapping
Sep 8, 2010
68
7
Charlestown, Cornwall
Funster No
13,611
MH
Coachbuilt
Exp
25
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.

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 !)
 

Jaws

LIFE MEMBER
Sep 26, 2008
23,821
71,977
Thetford Norfolk
Funster No
4,189
MH
C class, Chieftain
Exp
since 2006 ( I think ! )
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 ! :ROFLMAO:
 

Wow

Trader - Engine ReMapping
Sep 8, 2010
68
7
Charlestown, Cornwall
Funster No
13,611
MH
Coachbuilt
Exp
25
Yes do come and have a chat, :thumb: I always say its worth trying if the improvements aren't good enough then no harm done, we can reverse it give you your money back and remain friends.

A tip I had from a customer in Wales who had a reasonable size A-class with a 2.8 and regularly gets more than magic 30. I followed his tip and it does work.
On one of those horrible rainy days watch or get someone to watch out of tha back window when you are crusing. At a certain speed 50-70?? suddenly the rear window starts to get really dirty as the flat rear causes havoc with the aero dynamics, back off a couple of miles per hour and you lose that draw back effect - that then becomes a very good economical cruising speed.
If you remember Swift used to add a wedge on their vans anf caravans to try and do something about it, obviously didnt work!
My van optimum is about 57-58mph but each will be different, but just a few mph more then consumption definately suffers out of proportion with speed gained. :Smile:


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 ! :ROFLMAO:

Subscribers  do not see these advertisements

 

Join us or log in to post a reply.

To join in you must be a member of MotorhomeFun

Join MotorhomeFun

Join us, it quick and easy!

Log in

Already a member? Log in here.

Latest journal entries

Funsters who are viewing this thread

Back
Top