P38 Mpg Diesel?

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lanny90

lanny90

Member
Posts
65
Location
South Notts
Just got myself 1997 p38 auto diesel and checking mpg its doing about 18mpg not driving hard , is this the normal? i thought it may have achieved a bit more, wondering if a problem, new engine fitted with only done 64k
 
Hi, I posted the mail, "is this a SLUG or what", the reply I had was, " That's what gives the low mpg figures, the near constant acceleration of a 2+ ton car, especially in urban areas getting up to 30-40mph all the time",........especially as it seems so underpowered. Im now considering a "powerbox" or the "chip" upgrade, - the guys here have advised me that you get better economy and the added bonus of extra power too, (good thing is, its not too expensive either).

I'll keep the list posted as to results when sorted
 
Hiya,

I've had my 2001 Diesel auto for about a month now. Worked out my mpg brim to brim as message centre reading is way out. I'm getting around 21 / 22 mpg. Managed to squeeze an extra one mpg after changing oil, oil filter, air filter, and running some Redex injector cleaner for a tank full.

Don't forget to check your tyre pressures as well as that can make a difference.

:)
 
Kungfu0210 said:
Hiya,

I've had my 2001 Diesel auto for about a month now. Worked out my mpg brim to brim as message centre reading is way out. I'm getting around 21 / 22 mpg. Managed to squeeze an extra one mpg after changing oil, oil filter, air filter, and running some Redex injector cleaner for a tank full.

Don't forget to check your tyre pressures as well as that can make a difference.

:)
Click to expand...

Tell me how you measure mpg brim to brim. I hear a lot of people saying this. Do you run it from full until it runs out of fuel. Maybe not. So if the message centre is so far out it must mean the sensors that feed it are giving incorrect readings. You must then be running from full to a certain point on the fuel gauge. One of the sensors is the fuel gauge sender unit, if that puts the red light on at varying times depending on what sort of surface your sat on, up hill, down hill, leaning left, leaning right. How can you know how much fuel in actually in the tank when the red light and refuel range >50 comes up. You cannot. There maybe another 100 miles in the tank or less than the 50 quoted. So this brim to brim stuff cannot work unless you fill the tank then run until engine stops. Not a good idea. It can only be a general idea of mpg using any other method given the known vagerancies of the P38 sender unit.
 
Eh ?

Brim to brim is exactly that. No P38 fuel senders involved. Fill your tank to the brim i.e. 1st click at your local garage. Reset your trip counter (mileage). Now drive as normal, go about your business, until it's time to fill up again.

Go back to the same garage, ideally same pump, and fill your tank again until the 1st click. Record the mileage on the trip, record the litres that you've just put in. Then you can do a quick sum and work out your mpg.

Yes there will be variability in the click point of the fuel pump, but at least going to the same pump reduces that slightly. Half a litre inaccuracy in the fill amount is minimal compared to the 80 odd litres that you are calculating this with.
 
wammers said:
Tell me how you measure mpg brim to brim. I hear a lot of people saying this. Do you run it from full until it runs out of fuel. Maybe not. So if the message centre is so far out it must mean the sensors that feed it are giving incorrect readings. You must then be running from full to a certain point on the fuel gauge. One of the sensors is the fuel gauge sender unit, if that puts the red light on at varying times depending on what sort of surface your sat on, up hill, down hill, leaning left, leaning right. How can you know how much fuel in actually in the tank when the red light and refuel range >50 comes up. You cannot. There maybe another 100 miles in the tank or less than the 50 quoted. So this brim to brim stuff cannot work unless you fill the tank then run until engine stops. Not a good idea. It can only be a general idea of mpg using any other method given the known vagerancies of the P38 sender unit.
Click to expand...

Brim to Brim is quite simple, you fill the tank to the brim (not to when the pump clicks off as they vary), you reset the trip recorder to zero, you travel as many miles as you fancy, you refill the tank to the brim, note the amount of fuel put in, note the mileage an the trip recorder, divide the miles by the gallons (having converted them from litres) and you have the miles per gallon. Absolutely no need to run to empty use the red light or anything else:D
I do this on every tankfull, I used to have to log it for business and it became a habit, it has often prived useful as an early warning of problems when the MPG has suddenly dropped off. It has recently shown up leak off pipes weeping on the P38.
 
Datatek said:
Brim to Brim is quite simple, you fill the tank to the brim (not to when the pump clicks off as they vary), you reset the trip recorder to zero, you travel as many miles as you fancy, you refill the tank to the brim, note the amount of fuel put in, note the mileage an the trip recorder, divide the miles by the gallons (having converted them from litres) and you have the miles per gallon. Absolutely no need to run to empty use the red light or anything else:D
I do this on every tankfull, I used to have to log it for business and it became a habit, it has often prived useful as an early warning of problems when the MPG has suddenly dropped off. It has recently shown up leak off pipes weeping on the P38.
Click to expand...

Yes brilliant Data will keep taking the pills. Senility is a wonderful thing.
 
I must agree with Wammers here ... Brim to Brim is a pointless excerise the "First Click" of the pump is only caused by "Back Pressure" or "Frothing" as you fill yer tank.

The ONLY way to check "BRIM TO BRIM" is to fill yer tank SLOWLY until it starts to overflow..... then drive until you fill it again & it overflows


the difference between Filling it "Quick" & filling it "SLOW" can be as much as a Gallon!!!!
 
the hooded claw said:
I must agree with Wammers here ... Brim to Brim is a pointless excerise the "First Click" of the pump is only caused by "Back Pressure" or "Frothing" as you fill yer tank.

The ONLY way to check "BRIM TO BRIM" is to fill yer tank SLOWLY until it starts to overflow..... then drive until you fill it again & it overflows


the difference between Filling it "Quick" & filling it "SLOW" can be as much as a Gallon!!!!
Click to expand...

Of course it does also help if you have a spare £100.00 to fill the tank with.
 
Amazing response chaps, thought it was just mine, under 20mpg the tuning box looks to be doing a good job at increasing fuel by about 25% may consider one but its my weekender at moment {cant afford all week at moment lol}
 
griffo said:
I have only just had my 1st p38 and was gutted when I first had it Iwas only getting 19mpg out of mine until I fitted a power box much better to drive and 24/25mpg and thats about town I havnt tried it on a run yet... try this link Range Rover P38 Diesel PSI Power Tuning Chip 95-99 on eBay (end time 20-Apr-10 20:04:19 BST)
Click to expand...

Do you have shares in the company? PSI powerbox is good tool, but gains it's extra power by injecting MORE fuel. As do ALL the other tuning chips.
MORE power MORE fuel. Injecting MORE fuel is the ONLY way of gaining more power and torque from an otherwise unmodified diesel engine. USE the extra power use MORE fuel. Simples.
 
wammers said:
Do you have shares in the company? PSI powerbox is good tool, but gains it's extra power by injecting MORE fuel. As do ALL the other tuning chips.
MORE power MORE fuel. Injecting MORE fuel is the ONLY way of gaining more power and torque from an otherwise unmodified diesel engine. USE the extra power use MORE fuel. Simples.
Click to expand...
all I can say is what I was getting before and what I am getting now the biggest improvment I have found with mine is the extra torque and the fewer gear changes mine has to make up the many hills on my doorstep it just pulls up most hills now in top gear with very little effort and a light right foot sorry your a none believer warrmers but I am very happy with it and in my books thats all that counts
 
griffo said:
all I can say is what I was getting before and what I am getting now the biggest improvment I have found with mine is the extra torque and the fewer gear changes mine has to make up the many hills on my doorstep it just pulls up most hills now in top gear with very little effort and a light right foot sorry your a none believer warrmers but I am very happy with it and in my books thats all that counts
Click to expand...

Not a none believer. If you are driving as you say at 60 mph up hill in cruise, yes i will take your point, the extra power and torque will allow the road speed to be maintained above torque lock and a speed were the box will change down. BUT you are using MORE fuel doing it. It is a fact of life you CANNOT get that sort of power increase other than by injecting more fuel. Maybe you save a bit not changing down as often and with the engine not having to rev as that happens. But not that much if any at all.
You CANNOT get more power and torque WITHOUT injecting more fuel fact of life i am afraid. But then again i have only been a diesel mechanic for 44 years so what do i know?
 
wammers said:
Not a none believer. If you are driving as you say at 60 mph up hill in cruise, yes i will take your point, the extra power and torque will allow the road speed to be maintained above torque lock and a speed were the box will change down. BUT you are using MORE fuel doing it. It is a fact of life you CANNOT get that sort of power increase other than by injecting more fuel. Maybe you save a bit not changing down as often and with the engine not having to rev as that happens. But not that much if any at all.
You CANNOT get more power and torque WITHOUT injecting more fuel fact of life i am afraid. But then again i have only been a diesel mechanic for 44 years so what do i know?
Click to expand...

Standard : 150 HP 110 kW 330 Nm
PSI : 170 HP 125 kW 375 Nm
The PSI Powerbox increases horsepower, torque and can improve fuel consumption making for a more efficient vehicle.
The power increase is achieved by dynamically re-mapping (in real-time) the can-bus digital data between the fuel pump and ECU to provide extra fuelling to the engine at the most necessary points, in strict accordance to engine speed and load.
The PSI Powerbox micro-management system works in parallel with the original management system to ensure the smoothest delivery of power and torque. Because the Powerbox can increase torque, pulling power and acceleration, :):):)you will save on fuel with the number of miles per gallon achieved.:):):) Added torque also means you can hold higher gears at lower speeds as well as enabling you to change up through the gears faster - meaning you burn less diesel.
As well as these features, its worth bearing in mind how compact your Powerbox will be. Not only that, it can even be fitted using the original manufacturers plugs, usually in twenty minutes or less. In any case, full colour instructions are included with every PSI Powerbox and our support team can help with any installation or technical queries you may have. Once your Powerbox is installed no further adjustments will be required, as each one has four individually programmed fuel maps specifically for your make and model of car. The box is also extremely hard wearing, being shock resistant as well as waterproof but is traceless once removed, so it will not interfere with your car warranty.

and it does what is says on the tin!!!! My dad has been a mechanic for over forty years too and a dam good one at that:) but things change mate technology waits for no man I am affraid
 
griffo said:
Standard : 150 HP 110 kW 330 Nm
PSI : 170 HP 125 kW 375 Nm
The PSI Powerbox increases horsepower, torque and CAN improve fuel consumption making for a more efficient vehicle.
The power increase is achieved by dynamically re-mapping (in real-time) the can-bus digital data between the fuel pump and ECU to provide extra fuelling to the engine at the most necessary points, in strict accordance to engine speed and load.
The PSI Powerbox micro-management system works in parallel with the original management system to ensure the smoothest delivery of power and torque. Because the Powerbox can increase torque, pulling power and acceleration, :):):)you will save on fuel with the number of miles per gallon achieved.:):):) Added torque also means you can hold higher gears at lower speeds as well as enabling you to change up through the gears faster - meaning you burn less diesel.
As well as these features, its worth bearing in mind how compact your Powerbox will be. Not only that, it can even be fitted using the original manufacturers plugs, usually in twenty minutes or less. In any case, full colour instructions are included with every PSI Powerbox and our support team can help with any installation or technical queries you may have. Once your Powerbox is installed no further adjustments will be required, as each one has four individually programmed fuel maps specifically for your make and model of car. The box is also extremely hard wearing, being shock resistant as well as waterproof but is traceless once removed, so it will not interfere with your car warranty.

and it does what is says on the tin!!!! My dad has been a mechanic for over forty years too and a dam good one at that:) but things change mate technology waits for no man I am affraid
Click to expand...


See highlights above. The word CAN has many uses.

Listen carefully i will say this once more. IF YOU USE THE POWER YOU WILL USE MORE FUEL. You will notice that the most efficient speed of a P38 is around 50 mph. You use less fuel at a constant 50 mph than you do around town stopping and starting and at 30 mph. If your P38 is different than this you are the only one that has one like it . Treasure it, it is a one off. I maybe wrong but as far i am aware the BMW unit in the Range Rover produces as standard 136 bhp, not the 150 bhp you quote above. Maybe you have it mixed up with a Omega or 525 Di.
 
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