P0300 P0174 P0171

[Rick#7]

Hey guys, my nephew just bought his 1st Mustang, a 2015 GT with MT82 trans and 46k miles. The car has a JLT intake, but no knowledge of any other mods. The test drive was fine, as was the drive home, but 5 minutes later the cel came on. A borrowed code reader returned these 3 codes, although the car still drives fine. A search of the forum gave us some thing to look for, but I wanted to ask if anyone has had this same combination of codes and could share what the ultimate outcome was to correct it?

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[Cobra Jet]

So from prior posts, most say if a used S550 has the “JLT” intake, it most likely has a tune as well. If the seller did not supply you with an external dongle for loading/modifying tunes, or you were not made aware of this - search out “JLT” on here and you’ll hit on a ton of threads….

The P0300 is a generic misfire code - very hard to tie back to specific issue, but it could be a number of things tripping it such as vac leak, throttle body, VCT’s, IMRC’s, crank position sensor, MAF, O2’s etc…. If it were a P3031-P0308, that would be a specific cylinder to check.

This thread may give you some enlightenment to Ford's misfire strategies:
https://www.mustang6g.com/forums/threads/good-tech-article-on-ford’s-misfire-strategy.108076/

Also here is a pdf snip from the Ford Shop manual. which is "Coyote" specific. I'm including it because it gives a bigger picture of how to diagnose misfire events from the generic to the actual cylinder event codes:.
https://www.mustang6g.com/forums/attachments/hd-misfire-detection-pdf.538665/

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P0171 = lean bank 1
P0174 = lean bank 2

Check this thread response and see if it helps with your P0171/P0174:
https://www.mustang6g.com/forums/threads/i-need-help-regarding-my-cai.86823/page-2#post-1941218