Technical MPG Drop – What can it be?

[Deckchair5]

Afternoon Argo
I'd guess the diesel set up would be similar but I can only say with certainty of my experiences with the 1.6. A MAF sensor does the same job as a MAP ie measuring airflow but in a slightly different way. How the diesel ECU copes with bad MAF sensor output would be very different i think. Diesel owners often say of a running out of breath when accelerating with a bad MAF

 

[stilosporting]

so ifd the map sensor was disconnected on a jtd you would still expect it to run ok? would you still get the beep engine failure? i ask as i forgot to connect it once and got the beeps so just plugged it back in.

i know it started as a 1.6 thread but hopefully is generic.

 

[Deckchair5]

No MAP sensor on a JTD and differently designed ECU so they don't correlate I'm afraid

 

[Argonought]

so ifd the map sensor was disconnected on a jtd you would still expect it to run ok? would you still get the beep engine failure? i ask as i forgot to connect it once and got the beeps so just plugged it back in.

i know it started as a 1.6 thread but hopefully is generic.

It's a MAF sensor on a JTD.

I think the answer is YES and YES.

I'd try to clear the logged fault codes if I was you :chin:

 

[stilosporting]

im 99% certain that the jtd DOES have a map sensor? there is a sensor that can get covered in gunk this is situated in the intake manifold in front of the egr valve. what is it if not the map sensor? i thought the map and maf did completely different things.

map for pressure and maf for air flow/density?

 

[Argonought]

im 99% certain that the jtd DOES have a map sensor? there is a sensor that can get covered in gunk this is situated in the intake manifold in front of the egr valve. what is it if not the map sensor? i thought the map and maf did completely different things.

map for pressure and maf for air flow/density?

It's just a similar device for the same application (to allow calculation of how much fuel to deliver based on amount of air drawn into engine).

JTD uses a MAF sensor which is between turbo and air filter.

How about providing a picture of this 'MAP' sensor you've seen

 

[stilosporting]

not just seen but had replaced about a year ago. its circled in red:

 

[Deckchair5]

All modern engines need an accurate way of measuring the volume of air going into the engine in order to put the correct fuel in for clean combustion. How it's measured is done in different ways.

MAF
Some MAFs measure intake volume through computing the air flow by measuring the current flow change through the cooling effect of air passing over a heated wire- (cooling means resisitance change which means different current flow).

MAP
Other engines compute the intake volume by measuring the air pressure, this is usually more reliable as the MAP sensor doesn't clog up or need routine cleaning

As the inside bore of the intake remains the same then some simple calcs produces the air volume going in allowing for some other variables like air temperature

They are there to do the same job ie measure the volume going into the engine and some engines will have MAP sensors and some will have MAF sensors. Maybe some JTDs have MAPs and some MAFs. It's difficult to generalise across the entire range of Stilos

 

[j0nny]

£50 of BP unleaded petrol and 333 miles range to empty, is it just me or is something up there?

 

[JFL]

£50 of BP unleaded petrol and 333 miles range to empty, is it just me or is something up there?

were you driving around a city/town after you have filled up

i once filled up in a town, and did the stop start routine back to route. checked my trip computer and had a range of only about 450 mile safter filling up , thats on a diesel.

filled up at a motorway service station right to the brim (work were paying ), got on the motorway, steady 70-80mph estimated range 590 miles or so

 

[j0nny]

yea, filled it in my local town, havent been too many long journey distances as uni has finished. but is that about right, 340 miles to a full tank of petrol in a 1.2?

 

[JFL]

there is a way of working out your mpg, but i cant remember it

350 miles from a 1.2 sounds about right to me

 

[stilosporting]

well i decided to disconnect the sensor and for the rest of the day had a non turbo diesel lol. reconnected it and then did the same with the maf sensor. seems to have picked up and the range to empty is giving better estimates so seems to have done some good

 

[Argonought]

....and then did the same with the maf sensor. seems to have picked up and the range to empty is giving better estimates so seems to have done some good

Yes; my experience is much the same regards MAF sensor (see ELM323 thread).

Seems these might need replacing more often than is realized.

The big question at the moment is :chin:

Is it safe to leave the MAF sensor disconnected (for say 800 miles) ?

 

[stilosporting]

there was a time i drove with it disconnected for about 5-10k miles lol as it ran better.

 

[NumanR]

Think about it guys, how can a jtd engine ecu monitor boost pressure if it doesnt have a map sensor? JTD engines have an airflow sensor in the inlet trunking and a map sensor in the manifold monitoring pressure, (negative and positive).

 

[Argonought]

there was a time i drove with it disconnected for about 5-10k miles lol as it ran better.

That's reassuring

I presume you eventually fitted a new one?

 

[coyotes_uk]

yea, filled it in my local town, havent been too many long journey distances as uni has finished. but is that about right, 340 miles to a full tank of petrol in a 1.2?

Whats the combined mpg for a 1.2? The 1.6 is 38ish, 1.4 must be high 40's so im guessing the 1.2 must be in the 50's?

 

[stilosporting]

That's reassuring

I presume you eventually fitted a new one?

yeah and it again made a good difference.

Think about it guys, how can a jtd engine ecu monitor boost pressure if it doesnt have a map sensor? JTD engines have an airflow sensor in the inlet trunking and a map sensor in the manifold monitoring pressure, (negative and positive).

:woot: i knew something lol cheers for the info NumanR

 

[JFL]

Whats the combined mpg for a 1.2? The 1.6 is 38ish, 1.4 must be high 40's so im guessing the 1.2 must be in the 50's?

youre praying, 50mpg from any 1.2 is quite good going

i would have said about 38mpg for 1.6
42-44mpg for 1.4
and maybe 46mpg for 1.2

but to achieve these you have to drive like a grandma

i used to do about 35-40mpg in my old 1.2 because it had to be thrashed everywhere (thats a 16v, small city car as well)