A

aerofabrique

Active Member
Hi all wondering if you can shed some light on this - ive read the other threads and theres mention of leaking ILPs and injectors.

It has a PSI and would easily get 30mpg on average according to the trip. Now its dropped just suddenly to 24 and struggles to go above. Yes I know I was lucky to get 30 in the first place but I want it back. Its strikes me something is wrong as it dropped off. I only use Shell diesel and have used 500ml of redex every other tank for the last 10 fill ups which may have something to do with it.

I've replaced the air filter and checked all pipes for delamination. Intercooler is free. Turbo lags when cold and the 'check engine light flickers' but goes off. I've just replaced the IAT sensor on the manifold after snapping the plastic protector on the resistor bit oops. No MAF sensor.

Could someone please tell me

1) How does the MPG calculator work logically? That may be able to help me trace the cause?
2) There seems to be a lot of oil under the oil filter housing and on the diff housing. At least i think its oil, doesnt smell like diesel. trying to rule out leaking FIP.
3) No air in the clear fuel line could it be the fuel filter blocked as I havent changed it but was only changed 2000 miles ago with service guidelines. Does injector cleaner clog filters?
4) no smoke white/black from exhaust so rules out head/turbo problem?

Any ideas be greatly appreciated or if
anyone else has experienced the same prob with a PSI box fitted.

Ash
 
I always thought the MPG is calculated using the fuel Gauge Sender unit indicating fuel quantity used and the trip 2 Computer for distance covered since last reset dvide on into t'other and you get MPG....

Others have said it counts the number and length of time the injectors 'squirt' for as they are supposedly metered to provide a certain amount of fuel over a certain period of time....

I have asked in a previous post if someone has a definitive answer (with proof) of how it is truly calculated....

But it will always be off by 10-15% anyway....best to use the Brim to Brim method.....fill up, do a bunch of miles, fill up again and note the quantity of fuel used and miles covered will give you the most accurate method.

IMO, Poor MPG can be down to poor ITP or leaky Leak Off Pipes...., Blocked MAP senser, or dirty Air Filter....just my twopenneth...
 
Last edited:
Any form of box will give rise to false MPG figures. The only true way to work it out is brim the tank then run it for a couple of weeks. Brim the tank again and calculate the MPG by dividing the number of miles travelled by the number of gallons used. You have to remember that temperatures have dropped aswell so it will take longer to warm up.
 
I keep a log of all the fuel to work out mpg and since april its averaged 29.62. The only anomaly with this is i dont brim the tank each time so i have to go by the gauge to see what the level is and compare it with what was left since the last burn. For info i use each notch as 11 litres as its a 90 litre tank giving 2 litres unusable fuel. Recent figures show a definiate drop off. I can confirm the on board computer is off about 18 % according to the spreadsheet.

Anyway, anorak aside, ive replaced the air filter so ruled out air on that side of the turbo. Whats the best way to check injectors? Is this best done with diagnostics?
 
Well at least they didnt put me on a fooking spread sheet to two decimal places.
 
Well if only I could see 30mpg I have just done the fip and it was failing and I'm now getting 23mpg instead of 16mpg I might have to invest in a psi if you can achieve 30mpg if I can get 25mpg round town I'll b well happy

The only way to test injectors is to remove and send to a specialist
 
Concur with Matt on injector test....

I, too, keep a spread sheet on Fuel consumption....I fill up every Monday lunch time to the brim, I usually do around the 300 mile mark from fill up to fill up, so the cost of filling up doesn't look to scary at between £72-80 a week instead of £120 every 10 days or so.....I know it is the same amount in the long run, but psychologically it doesn't hurt as much, today I managed 27.04 MPG, last week was 26.59 MPG and the week before was 26.33 MPG...so I am averaging arounf 26 and a bit with a mixture of motorway driving to work and Country Lanes and Down dales weekends and evenings....
 
Saint.V8 said:
Concur with Matt on injector test....

I, too, keep a spread sheet on Fuel consumption....I fill up every Monday lunch time to the brim, I usually do around the 300 mile mark from fill up to fill up, so the cost of filling up doesn't look to scary at between £72-80 a week instead of £120 every 10 days or so.....I know it is the same amount in the long run, but psychologically it doesn't hurt as much, today I managed 27.04 MPG, last week was 26.59 MPG and the week before was 26.33 MPG...so I am averaging arounf 26 and a bit with a mixture of motorway driving to work and Country Lanes and Down dales weekends and evenings....
Click to expand...

Sounds about in line with mine, I dont feel so bad now thanks! Still can't work out why it dropped off - I hope its the computer just not liking the bad weather and dark mornings!
 
aerofabrique said:
Sounds about in line with mine, I dont feel so bad now thanks! Still can't work out why it dropped off - I hope its the computer just not liking the bad weather and dark mornings!
Click to expand...
You have just answered your own question. The more demand you put on the system such as lights, wipers and heaters the more the MPG goes down.
 
Rob Edge said:
You have just answered your own question. The more demand you put on the system such as lights, wipers and heaters the more the MPG goes down.
Click to expand...

Even so the drop off was a couple of weeks ago when iwas using lights and wipers. To be honest i might just bite the bullet get a diaog and probably confirm my worst fears of a failing fip.
 
aerofabrique said:
Hi all wondering if you can shed some light on this - ive read the other threads and theres mention of leaking ILPs and injectors.

It has a PSI and would easily get 30mpg on average according to the trip. Now its dropped just suddenly to 24 and struggles to go above. Yes I know I was lucky to get 30 in the first place but I want it back. Its strikes me something is wrong as it dropped off. I only use Shell diesel and have used 500ml of redex every other tank for the last 10 fill ups which may have something to do with it.

I've replaced the air filter and checked all pipes for delamination. Intercooler is free. Turbo lags when cold and the 'check engine light flickers' but goes off. I've just replaced the IAT sensor on the manifold after snapping the plastic protector on the resistor bit oops. No MAF sensor.

Could someone please tell me

1) How does the MPG calculator work logically? That may be able to help me trace the cause?
2) There seems to be a lot of oil under the oil filter housing and on the diff housing. At least i think its oil, doesnt smell like diesel. trying to rule out leaking FIP.
3) No air in the clear fuel line could it be the fuel filter blocked as I havent changed it but was only changed 2000 miles ago with service guidelines. Does injector cleaner clog filters?
4) no smoke white/black from exhaust so rules out head/turbo problem?

Any ideas be greatly appreciated or if
anyone else has experienced the same prob with a PSI box fitted.

Ash
Click to expand...

Get it on diagnostics and check injector number 4 needle lift sensor. Otherwise a failed in tank pump seems to have an adverse effect on fuel consumption:)
 
Can overfilling the oil have such a noticible and adverse affect on fuel cons? I've noticed the oil is over filled by about 600ml and I'm not sure how sensitive these engines are to this. I've noticed a little leak from the filler cap down the side to the recess of #1 injector.

I think the injectors, in particular #4 have been replaced recently due to no visible fuel leaks in the recesses or from the leak offs. FIP and all connecting pipes seem clean and dry. I think though the sensor maybe knackered because, whichever numbnuts did it, trapped the sensor wire in the intake manifold from #4 between the manifold and block.

There's no rough running or problems starting hot or cold so I dont think its the fuel downstream of the filter problem. There is a rough run on occassions after a motorway run which I think is the old DMF problem but not serious enough to worry me yet!

Checked calipers and brakes but dont believe to be sticky as she tracks straight and true.

Diffs? judder at slow speed full lock left and full lock right?
 
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