A couple of weeks ago I posted regarding a tapping noise from the signum's engine which I suspected may be caused by a dicky injector.
To recap, there is a loudish tapping noise when the engine is cold, which gradually decreases as the engine warms up. It is worst during accelleration, and least on the overrun.
It is a 1.9cdti 16v of 2004 vintage, with nearly 120k on the clock. The noise has gradually worsened over the past year.
I finally got around to putting it on the opcom and checking the injection quantity deviation. The results were as follows (measured with a partially-warmed engine at idle):
Cyl 1: -0.25 mg/stroke
Cyl 2: 0.24 mg/stroke
Cyl 3: 0.53 mg/stroke
Cyl 4: -0.52 mg/stroke
From reading other posts on these forums, these would appear to be normal. Is that assumption correct? Is it therefore safe to rule out the injectors as the cause of the noise, or can they fail in other ways that cause noise but not show excessive deviation?
My mate was outside the car when I started it at the weekend and noticed that the tapping was very loud for the first couple of seconds after starting. He suggested that something (possibly a small end bearing or valve lifter) was noisy until the oil pressure had built up, and that it was unlikely to be diesel knock, therefore eliminating the injectors.
He suggested that given the inevitable mechanical wear resulting from the mileage, it would be beneficial to use a higher viscosity oil. However, I pointed out that due to the DPF, it must have an oil meeting GM spec LL-A-025 or LL-B-025. All the oils that I can find which meet this spec are 0w30 or 5w30, which seems to rule out that option.
Since I bought it two years ago, I've been using the GM synth dexos2 oil and changing it and the filter every 7-8k miles.
Anyone have any thoughts on these issues?