Thread: Turbo tuning

theres lots you can adjust if you're game enough but

1. generally you're only going to touch the low speed screw, max speed screw and the rack limit (aka fuel) screw

2. sort of... it changes the maximum fuel position or the rack so long as you have enough demand on compared to current engine speed the rack will move to the full fuel position, you dont have to have it pinned for this to happen.

3. Max boost is set by the turbo configuration, the wastegate is factored into this and is used to limit the maximum boost delivered from the compressor. playing with the actuator rod lenght gets you more or less boost upto the limit of the compressor and turbine combo

4. how hard you're working the engine. works reverse to petrol, diesels always run lean untill you fuel them up to get power, overfueling runs them rich and you get more exhaust temp this is what drives the turbo. the EGT gauge lets you know how hard you're working the engine very very roughly, boost is the engine attempting to make HP and EGT is it attempting to make torque.

5. not for the stock ex mil 4bd1t unless you retrofit a truck fuel pump. its intended purpose is to stop you from overfuelling at low RPM and reduce black smoke. it also, when setup and driven correctly, makes the engine more fuel efficient. it is possible to load up a turbo diesel without one in such a way that the pump is dumping all the fuel in, but the turbo is running too slowly so theres not enough boost, without the boost the EGT's go way high but because theres not enough flow rate coming out of the engine to spin the turbine hard enough to drive the compressor fast enough to get the boost up to increase the torque to allow the engine to accellerate to pump more gasses through the engine to start the whole prossess that makes the turbo work efficiently. Sit here for long enough and you'll just melt the pistons/head if you don't cook the engine first.

That really helped my understanding.

As for 5. - Can that state be avoided by not using heavy throttle at low RPM. Can it be fixed by backing off the accelerator?

yep, if you do it at the pedal you dont need the compensator,

Thanks again Dave, It's all making better sense to me now.

Is there any benefit to using an O2 probe to measure when you've run out of oxygen to mix with the fuel you're dumping in?

Even a fly-by-wire throttle to discourage those "without mechanical sympathy"?

Not really, once you get to no more O2 you will only have a 0 value reading for the gauge and no idea how far you've gone into the rich fuel zone.

in descending order of probable cost and effort.

Build up a set of O2 sensors and then make a fly by wire system along with everything you need to electronically control a servo to drive the mechanical system.

Buy and bolt up the IP with the boost compensator

Fit a boost and EGT gauge and drive the gauges.


If you can be so mechanically unsympathetic and you have the money to go and buy a shed class 4bd1 / -T and then bolt up a turbo and then over fuel it so much that you can melt the pistons and then you go and abuse it so much that you actually do manage to kill the 3.9 you should just go buy a new toyota or something else, Youve missed the ethos of owning a mechanical landrover by a mile and just managed to proove it.

I agree that some care and attention to the gauges is the way to go - and would suit me personally.

Some of us might have other family members drive their vehicles from time to time. Still better to "endorse" them