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Driving home last eveing my Disco felt as if the hand brake had been left on, it felt really tired, a quick glance at the boost pressure guage shoed that the boost wasnt going over 10 psi - normal boost on the hill in question is 14 -15psi. any ideas as to the problem? a jammed open relief valve could be one I guess :blink:

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No, mine is a very basic series 1 1988 version 300TDi, fully manual no electronics at all. I'll pull the manifold off on saturday and see if the relief valve is stuck in any way, the turbo is new having only done 20,000 kilometres since it was replaced. I couldnt feel any leakage from the hoses (Silicon) or the intercooler but I never checked the small hose to the Fuel Injection Pump that doubles as the pressure line to the waste gate pneumatic cylinder, so I'll check that as well. The only other line is the bundy tube to the 2' boost pressure guage on the dashboard - I'll check that as well. I noticed that the boost was hunting at around 10psi as if it was trying to get higher but something was stopping it so my feeling is the relief/waste gate but I'd be grateful for any other ideas.

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Okay, turbo fixed, I replaced the fuel filter, drained the water can under the tank, went for a test drive and there was no improvement so off with the maniflold and see what was going on. My first thought was that the dump valve flap could have been warped or even broken off the shaft, not so, the problem was far more unique.

Some time ago I fitted a EGT thermocouple into the manifold. In welding the fitting into the oval plate the plate warped meaning that I had an exhaust gas leak, the solution was to use a soft copper gasket, high temperature gasket cement and longer bolts to pull it down tight.

On inspection one of the bolts ends that was into the exhaust gas stream had burnt off leaving the small stub to migrate and wedge itself into the exhaust gas volute and thus effectively blocking it resulting in a reduced turbo revolution range thus poor puff - 10 psi instead of 14.7 !

Solution, with a pair of thin nosed pliers extract loosen and remove bolt end, blow clear with compressed air carbon and dust and reassemble and replace all the manifold assembly. Next was to take the Disco for a trial run and yessssss full boost. T

he only thing is I during this exercise I noticed that the bloody P gasket has a leak so the water pump will need to come off, oh well next weekend is a long one (Australia day Monday public Holiday) and I'd rather work on the beast than cut lawns.

Incidentally yesterday we had our HOTTEST day ever in Sydney since records have been taken, 46.8 degrees Centigrade - try working on a car in the open under those conditions :o just holding a spanner was painful

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