Superchip MPG advice

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whydididoit

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39
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Devon
I've fitted a PSI powerchip to my 1999 DSE, the difference in performance is very good but i now seem to be doing 20mpg and 24mpg on a run whereas before i was getting 25mpg and 31mpg on a run. Is this normal?
Plus the chip has an earth wire which you can connect to a switch to switch on and off, is this a wise idea or would it damage the pump?
I was thinking of switching it off when i'm tootling about to get better mpg but having it on for longer runs.
 
This has been discussed numerous times....

With a Diesel the only way to increase power/performance is to inject more fuel....hence the dip in MPG figures....

A petrol engine can be tweaked to give a bit of an increase and also achieve better MPG, as you can adjust fuel/air ratios etc....but a Diesel is a bit more complicated as the amount of air inducted remains almost constant so the only thing that can change to increase power is more fuel, cooler induction air, or a higher charge pressure from a turbo or similar.

The 'Claims' to increase MPG are based on the need to not boot it quite so much for quite so long to get up to speed, but when not needing that increased acceleration, it is overfuelling constantly to maintain the increase in output...and the only way to do that is to inject more fuel.
 
I have trawled through all the previous posts but couldn't understand why everyone else said it would improve mpg, do you think it would cause any problems to have the powerchip on a switch as i mentioned?
 
It all depends on many different things... How good the original maps are, and exactly what the tuner has done to modify them.

One other thing, that affects it more than anything else... Have you adapted your driving style to make use of the new power? Because that is the single biggest factor affecting fuel consumption - it only puts as much fuel into the engine as you demand via the throttle!!!
 
I have said this many times, but just to be clear i will say it again. The only way to get more power and torque from an otherwise unmodified diesel engine is to inject more fuel. You CANNOT have 30 BHP and increased torque without doing it. If you drive it like a nun you MAY get a slight fuel saving, and on the motorway or on a long run because of the slightly smoother mapping. But IF you use the extra power stop start around town you WILL use more fuel. The perpetual motion machine has not yet been invented. Hope that sorts things out for you.
 
Last edited:
When i had my PSI powerbox i installed a button inside the cabin and used the grey (earth) wire from the box to connect/disconnect it.
Had no problems with the pump.
 
whydididoit said:
I've fitted a PSI powerchip to my 1999 DSE, the difference in performance is very good but i now seem to be doing 20mpg and 24mpg on a run whereas before i was getting 25mpg and 31mpg on a run. Is this normal?
Click to expand...

With the box connected the onboard computer isn't getting the precise fuel data that it needs so your only way of getting accurate mpg figures is to record your mileage from top up to top up and do your own calculations.
 
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