Theory of Operation

To extract more efficiency in a diesel motor, a turbocharger is employed. This device has a turbine that is driven by exhast gas flow which spins a compressor thereby compressing the air fuel mixture. This pressurized mixture makes a bigger explosion in the engine which makes it more powerful and efficient.

The turbo itelf creates in excess of 2 bar (30 psi); to limit this to the 1 bar the car needs, a wastegate vents excess pressure to the atmoshphere. Factory spec is 0.9 to 1.0 bar, (about 15 psi) but they never came that way from the factory, most are in the 0.5 - 0.6 (about 7 psi) bar range. Calibrating this to factory spec makes a phenominal diference in performance.

When the turbo is doing it's thing, the motor will need extra fuel to go with the extra air. A device called an ALDA senses pressure and tells the injection pump to deliver more fuel.

Besides the wastegate, your engine is protected from the turbo going nuts by an overboost sensor that cuts off extra fuel if the boost exceeds 1.1 bar (about 16 psi). Without extra fuel the turbo gives you no extra power. Without the protection the wastegate and overboost sensor gives you, you'd melt your engine from the inside out.

If all these things are clean and to factory spec, your car is giving you optimal performance. You might not recogize the way your car accelerates - it's quite dramatic.

What To Do

First, make sure the valves are adjusted, the injection pump timing is accurate and the chain and tensioner are ok. You don't want to go increasing the power of your engine if the fundamentals aren't right.

Boost Sense

First, attend to the overboost switch and boost sense lines. They need to be good and clean. You can find that article here.

Wastegate

Next, adjust the turbo wastegate. It's not tough to do, but there are two different turbos: KKK and AirReasearch/Garrett. The latter has a spring that you have to remove to adjust the bolt that controls the wastegate pressure. It's a royal pig to get that spring in and out. The KKK just has a screw you adjust.

Now, there are two schools of thought on this. One has it that the adjustment should be made ever so slightly, checking boost pressure with every turn of the screw that controls the wastegate relief pressure. The other point of view is to jack it all the way over - so far that's means 1.0 bar pressure on every car thats been tried. The overboost protection will prevent your engine from getting too mush boost. It's your call which method you use.

Here's the method.

ALDA

Right, after you've adjusted the wastegate, you need to adjust the ALDA to add more fuel to keep up with the increased boost. You can read that here.

You're done! Try to wipe that silly grin off your face, ok ?

People to hot-rod deisels, look here to get a flavour of it.

Richard Sexton, Jan 2000