jez1342 wrote: from memory they should be around 180 Kohms.
And indeed, you were absolutely bang-on the values here. Many apologies for quoting rubbish off the top of my head. I checked my notes again this afternoon, and the centre two injectors were each 178kohms, very similar to each other. The injector that I most suspect of being the misfire culprit (cyl.1) was 56kohms in my notes. I decided to recheck it this evening, after having run the engine through to normal temperature, and the probed resistance directly at the connector pins on the injector itself was 18kohms to 21kohms (climbing slowly). The other end of the engine (cyl.4) is yet to be rechecked. I'm still not happy with that one either, but getting to the injector unit is more of a pain (under the breather/separator units).
I ran a test on the electrical system for cylinder balance, using the Pico Automotive Diagnostics Beta software, but unfortunately it was struggling a bit with the signal off the battery (no problems on signal strength, but only occasionally reported the cylinder balance trace with "out of bounds" error messaging). I used the same setup on the battery with the normal oscilloscope function (AC coupled, auto ranging) and the signal was a bit noisy, but with a bit of low-pass filtering at 100Hz, quite readable. I have attached the trace that I took, which with filtering at low-pass 20Hz (to remove alternator phase swings) shows a clear pattern of three strong cylinders and one weak cylinder. This gives me some confidence that I only have one injector to deal with.
I ran a thermoscanner check across the back of the exhaust manifold, and there is some correlating evidence of strong cylinders at one end of the engine, but cyl.1 is down a bit on temperature at idle. The trouble here is that the end cylinders on a common manifold are always going to read a bit lower than the centre branches, so the temperature drop might not be the whole story. Hence a last Pico trace tomorrow (whilst the injector on cyl.1 soaks in Tunap 103) with a signal off the cyl.1 injector harness, to "time" the misfire information on the attached trace.