This is the same X trail I posted about a while ago, 2.2 Dci.
A lot of work later (new chains,valves/head work,new turbo) and it now
*runs perfectly* but is difficult to start when cold. Hard to start when cold seems to be a common complaint with these...Once it has fired up, it behaves impeccably, fast idles as it should whilst warming up and no trace of missing or unevenness.
This car has had a new battery, glow plugs and main ground strap and have also tried the starter motor from a known good vehicle. Injectors have been tested by a diesel specialist for leakage, fuel delivery and response times. Alternator also tests ok. Obviously it has had the fuel filter changed and the pump seems to deliver the required rail pressure. (Target and actual FRP agree in diagnostics graphing)
If you do the usual trick of waiting for the glow light to go out and then repeat and wait 20 secs (by design the plugs are powered for 20 secs after light goes out) it will start after about 4 -5 seconds of cranking. (This engine also lights the glow plugs during cranking, which it is doing.) If you don't do this and try to start it as soon as the light goes out, it will crank for 30 secs or more before starting. Despite the glows lighting during cranking. Sometimes at this point it will throw spurious codes, usually crankshaft sensor - although it still shows the rpm and the waveform is still correct,(measured at ECM terminals using a 'scope) or EGR valve (replaced with known good) and occasionally various moaning about loss of CAN communications to various modules. I'm guessing this is because the ECM is upset about the voltage drooping from extended cranking.
The battery voltage is 12.6, dropping to 11.5 with the glows on and down to 9v when cranking. Now, while this sounds a little low to me, an otherwise identical model exhibits the same behaviour - except that one starts within a second, hot or cold and without needing the 'double glow trick'.
Have tried as many diagnostics comparisons to the other vehicle as I can think of, cranking rpm, fuel rail pressure, target pressure, temp sensors, crank and cam sensors, injector waveforms, air mass readings and there are no obvious differences. For the purposes of clarification the compressions are 320PSi, *but* so is the comparison vehicle...
Out of ideas now :(