Article: Somon Wood Photos:Simon Wood

I have been suffering from an apparent lack of boost, the green turbo light not coming on and the engine feeling down on power.

As a result of performing the diagnosis as detailed below I concluded that the high-pressure switch was not working. Basically, if I put the 71kpa (about 10psi, to convert kpa to psi divide by 6.9) to the high pressure switch the light didn’t come on, if I put it the other side of the switch it came on and there was a audible change to the engine note

for a Diagram to troubeshoot your Turbo system

From what I can work out there are three switches associated with the turbo. A low-pressure switch, a high-pressure switch and a turbo control switch.

When boost is present in the inlet manifold it should apply pressure to the high pressure switch which will then activate the turbo control switch and also apply pressure to the diaphragm on injector pump, which in turn alters the injector timing, in much the same way vacuum advance works of a petrol engine.


This Image shows the various hoses connected as per specifications and has the various switches labelled.

This image shows what I did to bypass the high-pressure switch. This resulted in the green turbo light working again, with it coming on at around 1800rpm, depending on throttle position. I can hear the turbo spoiling up far more than it did prior to the modification. And most importantly the engine is developing heaps more power. As an example; a couple of hills around my place saw me dropping about 40kmh from bottom to top and usually changing from back to either 4th or 3rd

After this modification I was able to get up the hills in top gear and only dropping 10kmh from bottom to top. The engine appears to be running marginally cooler too, but about a needle width on the gauge. Not much I agree but I was a little concerned that it may run warmer. I think I can put the cooler running down to the injector timing, like I said above much like vacuum advance on a petrol engine. If your ignition timing is out it can cause the engine to run hot.

I have made a few assumptions in coming to my conclusions but so far so good. It has certainly made the Surf even more fun to drive.

I am however going to try and source a new high pressure switch and see how that goes.

If any one wants any further info or wants to discuss any of this please feel free to contact me via email, mon69@tpg.com.au.