Which is correct: "troubleshooted" or "troubleshot"?

The etymology of troubleshoot - the words trouble+shoot - mean that it follows the same rules as shoot itself. The past-particple of which is shot, not shooted.

"I troubleshot it" is correct, even if it sounds odd. That's English for you!

To troubleshoot is the verb in the to-infinitive form. From Merriam-Webster:

Present: I troubleshoot it.

Simple Past: I troubleshot it.

Present perfect: I have troubleshot it.

Troubleshot sounds wrong perhaps because it's a backformation from noun troubleshooting. In which case, the correct procedure would be to regularize it as 'Troubleshooted' but that's even worse.

(This is why you have "flied out" in Baseball and "mother-in-laws" for multiple MILs.)

My advice? Go with "fixed".

I have done lots of troubleshooting and it never occurred to me to say either "troubleshot" or "troubleshooted", of course I never thought about it either.

But I did talk about it and guess what I said... "I have been troubleshooting".

So it may lose some points for being not simply a preterite tense but it wins more points for being perfectly natural.

(It doesn't work for the other modern defective verb, input though)

Why do you assume that troubleshoot takes an object? If you treat it as intransitive, the problem doesn't arise: I troubleshoot for a living, and I was troubleshooting last week, but ?"I troubleshot." (with full stop) would hardly ever be used. Daydream is similar: I often daydream, and I was daydreaming half an hour ago, but you never have to decide whether the perfect tense is ?daydreamt or ?daydreamed (unless in a phrase like "I daydreamed you were in love with me", which I think is extending the word too far).

Google Ngrams shows that the commoner form in print is "troubleshot".

But regardlesws of past usage, which pattern should "troubleshoot" follow? "Troubleshoot" is a verb of the form <A><B> where <B> is a verb. There are two possibilities:

1. <A><B> is derived from the verb <B> by compounding. In this case, <A><B> inflects like <B>.

2. <A><B> is derived from another word <A><B> by zero derivation. In this case, <A><B> inflects regularly.

Example of case 1: "understand". It's a compound using the verb "stand". Hence "understood". No matter that it doesn't literally mean a sort of standing.

Examples of case 2: "highlight", "shoot" w.r.t. plants shooting

There is no prior word "troubleshoot" from which the verb was derived; rather, the verb is a compound of the verb "shoot". Hence "troubleshot".

Here are four discussions of the question from U.S. usage authorities (or commentators) who have substantial followings.

First, from Barbara Wallraff, Your Own Words (2004) [combined snippets]:

"A TV commentator recently referred to a new software package as having been troubleshooted. Does a suitable past-tense verb exist for something that has undergone a troubleshooting process?"

Here, too, we have a back-formation: troubleshooter was the original word. (Though NOAD [New Oxford American Dictionary] calls troubleshooter a derivative of the verb, not even its big sister the Oxford English Dictionary agrees.) So the form troubleshooted is less crazy than it may sound. NOAD fails to specify that the past tense of the verb is irregular, as it does with overshoot (overshot), and its front matter doesn't tell you to refer to the root verb (shoot)—— so it seems implicitly to be calling for troubleshooted. The RHUD [Random House Unabridged Dictionary] actually gives troubleshooted as a variant, together with troubleshot. WNW [Webster's New World College Dictionary] doesn't give the verb at all, past, present, or future—only troubleshooter and troubleshooting. However, the other dictionaries either explicitly or implicitly (as in, W3's [Webster's Third International's(?)] front matter does tell you to look under the root verb) are in favor of troubleshot.

Second, from Bryan Garner, Garner's Modern American Usage, third edition (2009):

troubleshoot > troubleshot > troubleshot. So inflected. The erroneous past-tense and past-participial form troubleshooted sometimes appears—e.g.:

• “Throughout the evening she troubleshooted {read troubleshot}, greeted guests, mourned the winning low bid on a set of top-notch golf clubs placed by mistake on the silent-auction table, and worried about how the crowd was responding to the new location." Nancy Bartley, "Far East Gala II," Seattle Times, 16 Sept. 1991, at C2.

...

Language-Change Index[:] troubleshooted for troubleshot: Stage 1

Garner's Language-Change Index attempts to provide a scale for measuring the extent of tolerance or acceptance of a particular "linguistic innovation" is; the scale ranges from 1 ("rejected") to 5 ("fully accepted"), with the implicit understanding that a stage 1 expression can accede to stage 5 in the fullness of time. Garner's placement of troubleshooted at stage 1 means that it has only begun its journey toward full acceptance and still mist pass through the intermediate stages of "widely shunned," "widespread but ...," and "ubiquitous but...." In the fourth edition of Garner's Modern American Usage (2016), troubleshooted remains at stage 1 (in Garner's estimation). Garner puts the current frequency ratio of troubleshot to troubleshooted at 10 to 1.

Third, from Steven Pinker, Words and Rules: The Ingredients Of Language (2015):

When a noun gets verbed, people use the regular past tense, even when the verb sounds irregular [cross-references omitted]: We ten-runned 'em (ended the game with a ten-run lead). • the haircutted amount (from haircut, a discount posted against a loan) • She really blinged it up (decked herself with bling, i.e., jewelry). • It's not so loud that you're going to be overbeared by it (from overbearing). • I have not troubleshooted yet (from troubleshooting).

And fourth, from Helen Cunningham & Brenda Greene, The Business Style Handbook (2012) [quoted language not visible in snippet window]:

troubleshoot One word. The technology team began to troubleshoot the problem as soon as the CIO became aware of the issue. Although troubleshot is technically correct for the past tense (rather than troubleshooted), troubleshot sounds odd and is best avoided.

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Conclusions

The authorities seem to be all over the map on this question. Wallraff says that the source noun for the back-formed verb is troubleshooter while Pinker says that it is troubleshooting. As for the proper form of the past tense, Pinker says that it is troubleshooted, Garner says that it is troubleshot, Wallraff says that authority can be found (with some difficulty) for both forms, and Cunningham & Greene simply advises writers not to use the past tense of troubleshoot at all.

In the world of published writing, Garner's argument about the predominance of troubleshot over troubleshooted seems to be on pretty firm ground. Here is an Ngram chart for troubleshot (blue line) versus troubleshooted (red line) for the period 1930–2005:

(In case the chart continues to be unviewable for some reason, you can find Ngram's graph version of the chart here.)

The ratio doesn't appear to be 10 to 1, but it is at least 3.5 to 1, and the pool of source material includes language-and-usage texts in which both forms are mentioned in the context of which one is preferable—a situation that to some extent artificially reduces the ratio by which the more common form of the expression dominates usage in the wild. The chart also indicates that troubleshot (earliest confirmed Google Books citation: 1942) is substantially older than troubleshooted (earliest confirmed Google Books citation: 1974).

I don't see any practical reason to use a different ending for the past tense of troubleshoot than I would use for the past tense of overshoot, which is clearly -shot. However, writers have differed with regard to the past tense of troubleshoot, and respected advocates for both options have come forward with more or less reasonable arguments for their preferred positions.