تنگی لوله سوخت فشار قوی

One of the short rigid pipes from the rail to an injector, restricted internally. It affects one cylinder only, which is what separates it from every other fuel supply fault — a restriction upstream of the rail starves all of them equally.

So the presentation is a single-cylinder misfire or contribution fault that survives an injector swap. Moving the injector to another cylinder moves nothing, because the pipe stayed where it was — and that test, which normally identifies a bad injector, points here when the fault refuses to travel.

Debris from a failed pump is the usual cause, which matters: if one pipe is contaminated the others and the injectors are too, so a pump failure means the whole high pressure side needs cleaning or replacing rather than one pipe. These pipes are single-use — the sealing cone deforms on first fitting, so one that has been removed should not be refitted.