Not yet, waiting to run it down (which at this rate shouldn't take too long!) But i can already tell the consumption is far higher just because 9 days ago, I put £30 in (about 25-26 litres) and usually this would easily last 2 weeks, often 3. and its already down in the last segment. And this is while i'm actually driving more efficiently than I normally would!
Technical JTD owners with poor mpg - then read this!
- Thread starter blackrat001
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Technical JTD owners with poor mpg - then read this!
Well mine has currently got 36.9mpg on the trip computer. Im going to wales on saturday and will brim the tank on bp ultimate which i have been using for the past 6 weeks with no apparent increase in mpg.
And when i get back i will brim the tank and see what that gives me.
My trip computer was always about 3mpg out (high side) but i have seen 49mpg but that was a doddle up the moterway with the cruise set at 70mph.
And when i get back i will brim the tank and see what that gives me.
My trip computer was always about 3mpg out (high side) but i have seen 49mpg but that was a doddle up the moterway with the cruise set at 70mph.
Just checked it on Fiat ECU Scan and the ECU has a "desired intake air quantity" of around 300mg/i when at idle. The MAF sensor is returning more like 40-50mg/i. I'm guessing this isn't right, so could this cause such poor economy?
The sensor was clogged, but now its completely clear and reading the same.
The sensor was clogged, but now its completely clear and reading the same.
i find this a very intresting topic as ive just witnessed the same on my jtd mw.
we went to legoland on sat and everything was fine on the way down there, 52mpg when we arrived (old habit of mine to check on long journeys).
we got stuck in the park for 3hrs when leaving- when we finally escaped i reset trip b again and the car came in at only 45mpgs, now i stolled home at a steady 65mph - the only difference was i had the pre heater fault appeared (sitting in all that traffic turning the car on and off killed a plug i think).
both journeys are 90% motorway work, infact i hit a bit of traffic on the way there and none on the way back so i was suprised at the fuel consumption on the return.
defo think i will find the dud and change it now.
roy
we went to legoland on sat and everything was fine on the way down there, 52mpg when we arrived (old habit of mine to check on long journeys).
we got stuck in the park for 3hrs when leaving- when we finally escaped i reset trip b again and the car came in at only 45mpgs, now i stolled home at a steady 65mph - the only difference was i had the pre heater fault appeared (sitting in all that traffic turning the car on and off killed a plug i think).
both journeys are 90% motorway work, infact i hit a bit of traffic on the way there and none on the way back so i was suprised at the fuel consumption on the return.
defo think i will find the dud and change it now.
roy
I've read the whole of this thread and I must say everything seems pretty normal to me. Although I only own petrol engines, the consumption of what you have is exactly within range. Or would you like to see how my dash shows 9.7 MPG?
It really depends on how you drive the car and where. If you're stuck in traffic for an hour, your engine consumes 0.7 l per hour just standing there. If in an hour you only travel 4 miles, it would pretty much explain the figures you are getting.
@Argonought: the things you check when traveling at speed and then decelerating is an inertia effect. Once you gain speed, your engine will reach a balance where it would consume the optimum amount of gas to move the car.
If you keep accelerating and decelerating you are making the engine move through the inertial forces and speeding up the car. When decelerating, the inertia tends to keep the car at the steady speed and your engine needs to pull a lot less to keep it at the right speed, thus ruining the inertia balance. That's why you get lower MPG although the car seems to run fine.
The most efficient way to travel and get the most mpg possible is to accelerate to the right speed and keep your foot steady on the accelerator. You will see that after keeping it steady for a few miles the consumption will decrease. I can get 40MPG at 68 MPH just by doing so.
I think your cars are fine. Its all down to how and where you drive it.
It really depends on how you drive the car and where. If you're stuck in traffic for an hour, your engine consumes 0.7 l per hour just standing there. If in an hour you only travel 4 miles, it would pretty much explain the figures you are getting.
@Argonought: the things you check when traveling at speed and then decelerating is an inertia effect. Once you gain speed, your engine will reach a balance where it would consume the optimum amount of gas to move the car.
If you keep accelerating and decelerating you are making the engine move through the inertial forces and speeding up the car. When decelerating, the inertia tends to keep the car at the steady speed and your engine needs to pull a lot less to keep it at the right speed, thus ruining the inertia balance. That's why you get lower MPG although the car seems to run fine.
The most efficient way to travel and get the most mpg possible is to accelerate to the right speed and keep your foot steady on the accelerator. You will see that after keeping it steady for a few miles the consumption will decrease. I can get 40MPG at 68 MPH just by doing so.
I think your cars are fine. Its all down to how and where you drive it.
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i think your actually missing the point, 2 journeys both identical in everyway, speed traffic load etc. yet journey 1 returns X amount to the gallon, and journey 2 returns Y (Y being lower).
There is only one real difference - a glow plug fault.
ive backed this fault up after going to work - my mpgs are now at 42mpg, on average i was getting 50mpgs before the glow plug failure (on work runs that is - london traffic).
seems really weird that a glow plug can affect fuel consumption in any way and thats what the thread is about.
ive got 1 petrol stilo and also had one previously that i wrote of, and i know these figures are amazing in comparison to yours, agreed they are within limits but we live with our cars day in day out and know if there is a problem with the amount they consume suddenly changes.
roy
There is only one real difference - a glow plug fault.
ive backed this fault up after going to work - my mpgs are now at 42mpg, on average i was getting 50mpgs before the glow plug failure (on work runs that is - london traffic).
seems really weird that a glow plug can affect fuel consumption in any way and thats what the thread is about.
ive got 1 petrol stilo and also had one previously that i wrote of, and i know these figures are amazing in comparison to yours, agreed they are within limits but we live with our cars day in day out and know if there is a problem with the amount they consume suddenly changes.
roy
Driving style, type of journey your making like multiple short school and shopping trips. The amount of traffic in the area you live all make a huge differences to fuel comsumption.
Comparing each others fuel consumption only really works if we all drive exactly the same on the same road with the same amount of traffic etc.
I live very close to Junction 10 of the M6, traffic around here is terrible. Most of our daily journey's are short, stop start trips to the school and shops so our car drinks the fuel, averaging 38Mpg before the school holidays. While the kids were off we spent a few days at a friends house. He lives out in the sticks North of Stafford. Due to the traffic being much less, journey's much longer and my wife driving our car gave 57Mpg. Proving my point to some extent.
I can deffinately say one thing has made a huge difference to fuel consumption on both our cars, replacing the MAP sensor. I'm not sure why but installing a new Map Sensor(£20) really did make a big difference. I'm guessing its because the MAP sensor directly effects what the turbo does so some how replacing the sensor gives better control of the turbo resulting in better MPG. Our MAP sensor was like most others and slowly deteriorated over time reducing the MPG then one day completely failed, no power at all. Once changed fuel consuption improved a lot so when I purchased our Multiwagon and consumption was a bit pants I changed the MAP and got instant improvements in fuel consumption.
I thought it was about poor MPG?
A glow plug cant directly effect fuel consumption of a warm engine.
I don't see how thats possible? The ECU uses default settings to overide certain failed components but as a glow plug is only used untill the engine is warm enough to sustain an efficient burn, I don't think any default settings are used so it shouldn't effect the MPG of a warm engine?
Or can someone explain how. :shrug:
Comparing each others fuel consumption only really works if we all drive exactly the same on the same road with the same amount of traffic etc.
I live very close to Junction 10 of the M6, traffic around here is terrible. Most of our daily journey's are short, stop start trips to the school and shops so our car drinks the fuel, averaging 38Mpg before the school holidays. While the kids were off we spent a few days at a friends house. He lives out in the sticks North of Stafford. Due to the traffic being much less, journey's much longer and my wife driving our car gave 57Mpg. Proving my point to some extent.
I can deffinately say one thing has made a huge difference to fuel consumption on both our cars, replacing the MAP sensor. I'm not sure why but installing a new Map Sensor(£20) really did make a big difference. I'm guessing its because the MAP sensor directly effects what the turbo does so some how replacing the sensor gives better control of the turbo resulting in better MPG. Our MAP sensor was like most others and slowly deteriorated over time reducing the MPG then one day completely failed, no power at all. Once changed fuel consuption improved a lot so when I purchased our Multiwagon and consumption was a bit pants I changed the MAP and got instant improvements in fuel consumption.
I thought it was about poor MPG?
A glow plug cant directly effect fuel consumption of a warm engine.
I don't see how thats possible? The ECU uses default settings to overide certain failed components but as a glow plug is only used untill the engine is warm enough to sustain an efficient burn, I don't think any default settings are used so it shouldn't effect the MPG of a warm engine?
Or can someone explain how. :shrug:
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Wind have have an impact as well as the above. Plus the difference is very small. Maybe you were in a little hurry. Maybe you've caught more than one traffic light. The possibilities are endless.
Less than one liter of fuel per 100 km/h is incredibly small difference. I would put more than that to the wind even, really.
Less than one liter of fuel per 100 km/h is incredibly small difference. I would put more than that to the wind even, really.
There's nothing normal about very poor consumption figures on a JTD (say sub 40mpg). It's a surprisingly complex issue and I'm not sure that anyone has really got to the bottom of it yet :chin:
You should read post # 37 more carefully as it's actually very counter intuitive.
Interesting observation on affect of MAP sensor on fuel consumptionI can deffinately say one thing has made a huge difference to fuel consumption on both our cars, replacing the MAP sensor. I'm not sure why but installing a new Map Sensor(£20) really did make a big difference. I'm guessing its because the MAP sensor directly effects what the turbo does so some how replacing the sensor gives better control of the turbo resulting in better MPG. Our MAP sensor was like most others and slowly deteriorated over time reducing the MPG then one day completely failed, no power at all. Once changed fuel consuption improved a lot so when I purchased our Multiwagon and consumption was a bit pants I changed the MAP and got instant improvements in fuel consumption.
Have you actually read this thread as you seem to be repeating previous questionsI thought it was about poor MPG?
A glow plug cant directly effect fuel consumption of a warm engine.
I don't see how thats possible? The ECU uses default settings to overide certain failed components but as a glow plug is only used untill the engine is warm enough to sustain an efficient burn, I don't think any default settings are used so it shouldn't effect the MPG of a warm engine?
Or can someone explain how. :shrug:
I've read it again and still think that is the reason why you get those figures, more or less.
It's simple physics.
Glow plugs are there to help the engine start when cold. That's about the only role they ever play. Apart from that, they are just another piece of metal inside the engine.
It's simple physics.
Glow plugs are there to help the engine start when cold. That's about the only role they ever play. Apart from that, they are just another piece of metal inside the engine.
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So did I, unlkike some others.
All evidence does suggest that the glow plugs play no part what so ever in effecting the MPG of a warm engine. But some do feel that they do. For example:
So just like Chris Tarrant, I called a friend(deisel mechanic). He said.
"there's no way glow plugs could effect MPG of a warm engine as some cars dont use them at all if the engine temp is high enough. BUT, a faulty temperature sensor could give false info to the ECU and cause the plugs to be used for longer and more fuel injected, reducing MPG"
"Error codes would be dependant on the type of vehicle, and if it was monitored"
When confronted with observation (especially when that observation is repeated by an number of owners) then an explanation is normally sought.
My personal view, as I've said before, is that I can't see how how heater plugs could directly affect mpg (at least not in a way that's measurable) so I've looked for other explanations to account for this.
We can discount temperature sensors (as only a heater plug is replaced to resolve this) but it could well be related to behaviour of the ECU which might behave in a different way if a fault with the heater relay is detected during start-up say :chin:.
I'd say it's still very much an open case until someone can provide an explanation.
Simple physics is not based on contradictions.
You need to decide which will produce the best mpg:
- Accelerating up and down but keeping to an average of 60mph.
- Carefully keeping to 60 mph
I've stated based on observation that 1 is best which is why I asked you to carefully read post #37
From your post above you seem to be saying 2 is best - but then you say my observation is perfectly normal.
This is a contradiction!
Accelerating up and down won't give you good mpg. You consume more gas accelerating and don't make up for it decelerating, because inertial curve is smaller than acceleration curve. Forces like environment (aerodynamics) and friction between components would decelerate your car while faster than being able to save enough fuel to compensate for the initial acceleration.
To be the same, you would have to accelerate hard and then pull out of gear until more than equal lower consumption can be registered, to give the car better MPG than cruising, but this would mean chaotic driving.
Car accelerated - 20 mpg
Car in cruise mode - 60 MPG
Car in idle - 80 mpg
Numbers are fictive.
Do the math. If you accelerate for 1 mile and then idle for another, the mixed consumption should be around 40 mpg. If my theory is right and inertia does give a boost of consumption for a limited period of time, then you would go a little higher to lets say, 45 mpg, but only for a limited period of time.
Keeping it completely steady would give you a constant 60.
See my point? Just my opinion, I may be wrong, but this is the way I see it. I haven't got a degree in physics or math, I graduated law and currently studying psychology
To be the same, you would have to accelerate hard and then pull out of gear until more than equal lower consumption can be registered, to give the car better MPG than cruising, but this would mean chaotic driving.
Car accelerated - 20 mpg
Car in cruise mode - 60 MPG
Car in idle - 80 mpg
Numbers are fictive.
Do the math. If you accelerate for 1 mile and then idle for another, the mixed consumption should be around 40 mpg. If my theory is right and inertia does give a boost of consumption for a limited period of time, then you would go a little higher to lets say, 45 mpg, but only for a limited period of time.
Keeping it completely steady would give you a constant 60.
See my point? Just my opinion, I may be wrong, but this is the way I see it. I haven't got a degree in physics or math, I graduated law and currently studying psychology
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I have got a degree in Physics, and I can't follow a thing that's being said here !
I don't disagree although it's much easier to consider in terms of the total energy of the vehicle (being a combination of potential and kinetic energy).
Provided the energy lost is not a direct result of retardation (frictional losses due to engine braking etc. as you've noted yourself), which would not otherwise also have been lost endeavouring to maintain a constant speed, then it matters little if speed is varied during a journey. On obvious theoretical gain is to allow speed to drop before a change in direction as this does indeed directly involve inertia
However, I'm having a little fun with you since you've clearly missed the point I intended to make in post #47 which was purely an observational post and NOT a theoretical one. If I make an observation which doesn't match what is expected in theory then it interests me to look for a reason. Something that only happens once can perhaps be discounted but when it's observed by 2 people and is largely repeatable then it becomes significant.
It's unfortunate you don't drive a JTD as otherwise we could pursue this at a more practical level
(which I think is a lot more interesting to most )right - i totally agree the glow plugs SHOULD play no part in fuel economy...
but the facts i have now infront of me tell a different story.
i changed number 2 which was open circuit, i test drove the car to and from work as a test before i changed the plug - over 110miles i was getting 41.2 mpg. (cruise control set to 60mph)
i changed it yesterday and the fault cleared,
110miles (excatly the same journey to and from work)
52.3mpg. (again cruise control set to 60mph)
I strictly stayed on cruise control set at 60mph both ways on both runs, infact i brimmed the car both times so there was the same amount of fuel each test, no more was loaded or unloaded to the car, everything was identical - the journey times were also within a min or so of each other (basically the same amount of traffic) - there wasnt anything else i could do to get like for like results as pointed out by another member.
with this im totally mythed,
this tells me that something does change in the fuel management system if a fault on a plug is present, or the plugs come on itermittantly whilst running, ive really no idea.
personally i suspect that its a bit of both - i dont think we will ever know unless a fiat tech comes on with all the knowledge.
my conclusion is if you get a glow plug failure then change it asap as it will drink more fuely.
i dont want to get into an argument, im just stating the facts as ive found them and also OTHER owners have also had the same findings, like they say where theres smoke.......
roy
but the facts i have now infront of me tell a different story.
i changed number 2 which was open circuit, i test drove the car to and from work as a test before i changed the plug - over 110miles i was getting 41.2 mpg. (cruise control set to 60mph)
i changed it yesterday and the fault cleared,
110miles (excatly the same journey to and from work)
52.3mpg. (again cruise control set to 60mph)
I strictly stayed on cruise control set at 60mph both ways on both runs, infact i brimmed the car both times so there was the same amount of fuel each test, no more was loaded or unloaded to the car, everything was identical - the journey times were also within a min or so of each other (basically the same amount of traffic) - there wasnt anything else i could do to get like for like results as pointed out by another member.
with this im totally mythed,
this tells me that something does change in the fuel management system if a fault on a plug is present, or the plugs come on itermittantly whilst running, ive really no idea.
personally i suspect that its a bit of both - i dont think we will ever know unless a fiat tech comes on with all the knowledge.
my conclusion is if you get a glow plug failure then change it asap as it will drink more fuely.
i dont want to get into an argument, im just stating the facts as ive found them and also OTHER owners have also had the same findings, like they say where theres smoke.......
roy
@Argonought I wouldn't be able to pursue this even if I wanted. We have 200 km of highway in Romania and it's always so crowded you can't really make any consumption test.
What I would like to add is the fact that what I explained below was just what I think would be the explanation of why you were seeing differences in fuel consumption a short period of time after accelerating. I agree with everything else that is being said, especially in the previous post. You were looking for a reason outside the theory when the reason was the theory itself.
I do believe, also, that road conditions vary one way and the other. For example you could be slightly climbing when going back and ultimately this would also have an impact on the fuel consumption. Doing the same road doesn't really help IMO because if, for example, wind blows 10 km/h more than yesterday, you're still off a little, although I agree that Roy has a point in what he's saying, the difference is too big.
Example: from my home town to the county capital there are about 25 km. No highway, national road. I drive exactly the same and still I get about 1 l extra on the dash when coming back.
You all have a point, and don't fully disagree with any of you, but it's hard to get an objective point.
So gentlemen, I will carefully read everything you say in the future and only intervene if something rattles inside my mind.
Cheers to everyone.
What I would like to add is the fact that what I explained below was just what I think would be the explanation of why you were seeing differences in fuel consumption a short period of time after accelerating. I agree with everything else that is being said, especially in the previous post. You were looking for a reason outside the theory when the reason was the theory itself.
I do believe, also, that road conditions vary one way and the other. For example you could be slightly climbing when going back and ultimately this would also have an impact on the fuel consumption. Doing the same road doesn't really help IMO because if, for example, wind blows 10 km/h more than yesterday, you're still off a little, although I agree that Roy has a point in what he's saying, the difference is too big.
Example: from my home town to the county capital there are about 25 km. No highway, national road. I drive exactly the same and still I get about 1 l extra on the dash when coming back.
You all have a point, and don't fully disagree with any of you, but it's hard to get an objective point.
So gentlemen, I will carefully read everything you say in the future and only intervene if something rattles inside my mind.
Cheers to everyone.
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So, it looks like we still have 2 unexplained observations of several JTD owners:
No one has yet picked up on a major error I made in post #57 (it's inferred so not that obvious)
Anyone spot it ?
- Reported Heater Plug Errors tend to lead to poor consumption [3 reports]
- Quick blasts of acceleration can lead to improved consumption (after speeds are allowed to drop to something more reasonable) [2 reports]
No one has yet picked up on a major error I made in post #57 (it's inferred so not that obvious)
Anyone spot it ?
