Well the readings are differant than I would have expected. Two milli volts is a large millivolt spread in reality. As you say I too suspect the glow plugs are new enough for your test.

Not certain but probable. You may want to swap the number two and three glow plugs to be certain though.

It almost looks like some cylinders 3&4 Are running somewhat hoter instead of cooler. This to me is not the source of the raw fuel supply smell in my opinion.

I will give this some thought as well. Glad to hear you have used the milli volt method before. The only thing now is I expect both the carbon build up and lack of it on some cylinders may be perhaps a lesser amount of base oil getting into some cylinders than others. Or the hotter cylinders are burning it off as it forms. They are running substantially hotter in my opinion. Still this does not hold water well as number four showed a lot of carbon.

On a careful check two milli volts is too high a differeance between cylinders at the same time. I would now be curious to see if someone timed the injection pump by ear as if advanced cylinders three and four are leading that much the engine should have knocked when setting the number one element properly by drip I suspect. This on diesel oil rather than wvo.

Then with those cylinders that retarded if timing was compensated by ear . This could be the unburnt fuel smell.

As you are well aware of the importanace of the glow plugs having simular charactaristics I believe it is worth the effort of swapping say the number two and three plugs to verify what you have found. Then proceed accordingly. Even at one volt at idle is a large amount of differance. Especially when the base values are in the 3-4 mil;li volt range. Actually representing a 25 percent differance.

I know on some engines showing only a fifteen percent differance have had issues. Usually knocking though. That is where only one cylinder had an elevated voltage reading. For other members that have never used the milli volt system used carefully and as intended it can indicate a a lot. Take short cuts and can be worthless.