possibly – nein, das Englische ist von Natur aus kompakter. Da wird m.E., u.U. nicht soviel abk.
M.f.G.
wundertype.de

I'm afraid there is no abbreviation for this in English.

P.S. I'm no mechanic, but "verstellter Zündzeitpunkt" is not "disguised (= getarnt/verkleidet/maskiert) ignition timing"

Ups, ja, das wäre z.B. vorzugsw. incorrect ignition timing

slipped ignition timing

Or: advanced/retarded ignition timing (if done on purpose)

oder misaligned ignition timing, aber das war nicht die eigentliche Frage.

Ergo habe ich bis jetzt nur die Aussage von #2, dass es keine Abkürzung gibt.

possibly – nein, das Englische ist von Natur aus kompakter. Da wird m.E., u.U. nicht soviel abk.

Three cheers for that comment!!!
Plus, a friendly reminder: Just because there's an abbreviation in the source text does not mean that an abbreviation is required in the target. (Although software translations are terrible in that regard. Full of abbreviations in the German, a limitation on the number of characters based on that text, and there are no sensible English abbreviations...)

Agree with the "no-abbreviation" comments.
how about "Errors on centrifugal advance - possibly pre-ignition...". ? abb. "poss."?
And sometimes at least u.U. could be "e.g."?

"u.U." translates to "under the circumstances", and definitely not "e.g.", but in this case its use is acceptable, as is "for example".

"u.U." is not "under the circumstances", but something like "under some circumstances". It can be translated as "possibly" or "sometimes". If an abbreviation is required for some reason, I agree with mikefm and Jim J. that "e.g." comes close to expressing the meaning here.

..."e.g.", but in this case its use is acceptable, as is "for example".

As others have mentioned as well, abbreviations simply are not used as often in decent English writing. While it may be possible to translate "u.U." as "e.g.," "e.g." is correctly not used as often as "u.U." and "z.B." are in German.

Note Martin-cal's comment: If an abbreviation is required for some reason,

Just because the German text has an abbreviation does not mean that one is required or even good in English. (Someone once posited that one of the reasons for this is that "e.g." comes from a Latin phrase [and thus you're throwing in a foreign language for no particular reason], while similar German abbreviations simply represent German words. I'm not sure I find that entirely convincing, but it does provide food for thought.)

e.g. (exempli gratia) als Übersetzung ist hier völlig ungebracht. Es setzt voraus, dass genannte Frühzündung als eine von mehren möglichen Auswirkungen auf jeden Fall eintritt. Dies ist aber faktisch falsch. Die Frühzündung tritt u.U. ein, d.h. sie kann unter gewissen Voraussetzngen eintreten, muss aber nicht. Deswegen favorisiere ich hier possibly.

Ich benutze da zuweilen einfach maybe. Bisher hat keiner gemeckert.

I have never heard of any abbreviation for circumstances permitting either.