TD5 lacking power

[lo-fi]

Afternoon! 

I don't mess with modern LR stuff much, and steer clear of the devil's fuel at all costs, but.... in the course of helping a friend with a poorly TD5 D2 at the weekend, I made some interesting discoveries (pun intended) and thought I'd pass on the experience. 

Symptoms were a lack of power over ~3000 rpm in higher gears. Up to 3K in fourth pulled fine, then it would seem to stumble, back off and rev no more as if you'd hit the limiter. He had done some research and come to the conclusion it was the turbo control valve, which we swapped over to find it made no impact on the problem. My next port of call was to check if the turbo wastegate was jammed. I have a little vacuum/pressure tester that we hooked up to the wastegate actuator, pumped up to 2 bar and resulted in a total lack of movement. The pressure held, which means the diaphragm was intact, but the lever was jammed solid. A few little tappy-tap-taps and working some Plusgas and milk of magnesia into the WG bearing soon freed it up and it all started working correctly, pulling cleanly right through the rev range. It would have been easy to assume a fueling problem - blocked filter, broken sensor or suchlike - but I'm glad I didn't. 

I think what's going on is that under 3k, there's little need to open the wastegate, it makes boost, fuels appropriately and all is well. Above that, boost keeps building as the WG is jammed shut, so at some point the ECU - being unable to keep the boost down - pulls fuel resulting in the judder and lack of power. In lower gears, the overboost doesn't manifest for long enough to cause a problem, so nobody is the wiser. A bit counter intuitive, but makes sense when you realise it makes sense to protect the engine and turbo. A broken actuator diaphragm could probably manifest the same fault, I suspect. Entirely my take, of course, but maybe it'll help someone out.

Milk of magnesia, in case you're wondering about it being an odd choice of lube, makes an excellent high temp anti seize compound, particularly on stainless. 

I left my mate with instructions to drive it like he stole it occasionally to keep the wastegate moving. 

HTH! 

Ian 

[Tanuki]

My 90TD5 does this every so often if I've only been pottering-around.

With the wastegate seized closed, if you give it some welly the boost-pressure goes way-high at higher revs/wider throttle-openings: this excess boost is fed [by the MAP sensor] to the ECU which will only allow it for a certain time before it switches to 'limp-home' fuelling in order to protect the engine.

If this happened during a journey I found I could temporarily clear it by coasting, switching the engine off and restarting it. Which sometimes caused confusion to the people I'd just overtaken.

Giving the wastegate actuating-arm a 'twatting' using a socket-set extension dribe and a small hammer frees the actuating arm off. I prefer not to use lubrication - well certainly nothing oily - on the point where the arm goes into the turbo-housing, as the heat will quickly reduce any oily stuff to a carbonised sticky mess.