economy tip, or just daft?

[yostumpy]

Whilst trying to eek out more mpg from the 110 (2.5 300tdi turbo deisel(best so far is 35.4mpg)) I was wondering about the turbo and the xtra fuelling. Suppose, (just humour me) one was to fit a solonoid valve type thing to the vacum pipe ? that goes from the turbo to the FIP,(the one that increses fuelling on boost) so that once up and running at speed , one could flick the switch and switch off the vacum line, so that you still had boost, but no additional fuelling. Then when needed it could be switched on again. Similar sort of thing to the cylinder deactivation on some new vWs ie if you dont need the power, switch it off. Now would this work, I mean the turbo boost on without the xtra fuel, would it give ANY xtra power, over 'no turbo' and would it cause it to run lean. Any reason not to. ok , you can laugh now.

[ksa8907]

the reason turbo chargers work is by using the expansion of the hot exhaust gas to power the compression on the intake charge. if you reduce the amount of fuel/heat going into the engine you will limit the amount of expansion able to turn the turbocharger.

beyond that, you will be running lean, how lean i don't know but that also cools the combustion.

its a nice "outside the box" idea, but im quite confident it won't do anything beneficial.

[UFO]

Diesels always run lean, so that should not be a concern. And you may slightly increase the combustion/thermal efficiency of the engine with extra boost, however I suspect you will not notice any mileage change as it's slight if any.

[wdb]

All the turbocharger does is increase the amount of air entering the combustion chamber. Either the computer, by keeping the injector open longer, or some other mechanism, adds fuel to match the extra air. Stopping the additional fuel altogether, with no other compensating changes, could cause you to run dangerously lean.

[Frank Lee]

^ It's a DIESEL. Won't run "lean". Doesn't get any "additional fuelling".

[pete c]

Wouldn't this have the same effect of simply backing off the throttle?

[ChazInMT]

The amount of power generated by a diesel is due to the amount of fuel burned. As long as enough air is present to burn the fuel charge, that's the power you will get. The turbo packs in more air to burn more fuel and get more power, so it's a feature that works during high power demand.

To run the turbo with out being in a high output mode would mean you are doing a lot of extra work to compress the air for the same power output. This adds up to a loss of efficiency. Plus if you screw with the controls and not know exactly how the engine management will react, you risk grave damage to your car.

[wdb]

Originally Posted by Frank Lee

^ It's a DIESEL. Won't run "lean".

Diesels certainly can run lean, but it does appear to be true (after some fevered googling ) that no harm will come from it except under very extreme circumstances.

Doesn't get any "additional fuelling".

Then what are we talking about here?

[320touring]

My old AAZ lump has Boost pin on the mechanical fuelpump. A vacuum line off the turbo sucks this pin up to increase fuelling whilst on boost.

certainly, its my (very limited) understanding that boost and fuelling should always decrease/increase together

[yostumpy]

Yes I want to interupt the boost hose to the FIP, so that it can be 'partially ' restricted, in a similar way to the VW 'umwelt' eco engine IIRC. but then be opened up to give me max power when needed.