When i boot it the boost gauge goes full scale and the warning light comes on. It's a bit smokey too but it goes well. I don't know if someone's got at it before and i realise they can take a bit more boost than standard but i don't want to blow it up! And as the boost gauge only goes to its standard maximum i've got no way of telling how high the boost pressure gets. At the moment i'm easing off when it overboosts but i intend to use the car for towing a heavy trailer which will make that tactic a little harder!
Is there a known fault that makes them overboost?
Is there anything i can do about it?
Thanks in advance. Ed
Sounds like the wastegate is stuck.
The boost gauge is a sensor on the down in the front left wing under the screen wash bottle. That usually does not register boost as the hose splits at the ends. The overboost light is a switch on the inlet manifold (battery end) by the fuel filter, that could be overly sensitive. The wastegate is a lever on the turbo assembly, high pressure trips the lever which dumps the boost pressure, this may be stuck or corroded, it gets very hot down there.
In my experience, only 2 TD's and 300,000Mi I know but better than nothing, I've never had the light come on, have one sensitive wastegate coming on early, but never one stuck closed though it can happen. Lots of blown / loose joints and a blown intercooler, but generally quite reliable for a FIAT.
To test the boost pressure you will need to remove the overpressure switch and replace it with a boost gauge. To read this on the road will be difficult / dangerous, so a rolling road would be better.
The TDs can be quite smokey but they do go very well. Both of ours smoke but always pass their emissions. The occassional a can of injector / fuel system cleaner works quite well in keeping the smoke and low end roughness down.
