Ok, so low afr means that bank is rich. Which can be either ignition failure (multiple reasons) or stuck open injector ( when figured with evidence of black/wet plug and P0304). Depending on locations, if coils and plugs are accessible, as a diag tech i have a neat inductive cop tester that just has wand i lay on top of coil,it blinks coil is firing, at least partially. It reads the magnetic field created falling as it fires plug. But for quick and dirty tests i swap lplug to another cylinder and coil to other one. Thus the issues if secondary ie cop or plug should follow defect/failure.
They make same device for injectors that detects click or coil xump on injector but simple mechancis stethoscope can possibly do that. Listen for click.
basic diagnostics and little sweat equity on your part can save bucks and teach you how to fix your car.
Another thing is buying a single car access to Alldata from Autozone.com. this will give you tech level info and procedures for repair, assembly/disassembly.
Some coils may fail electrically hot, few days later cooled down wahlah its "fixed". But only till it hits same failure again. Ignition coils/cables/plugs I have some preferences. Unless you totally modified engine to great degree, most times oem plugs, possibly different heat range work very well. As for me i love sbc/bbc engines and actually love tuning AC Delco plugs, trick to tuning them for NOS is watching for "bubbling" on ground strap. Much better than chasing Autolite (CRAP) misfires. NGK/Denso can cross brand lines, Motorcraft /AC Delco I can interchange with little issue. Chryco engines (not Mercedes or Mitsu) will run on Champion but i never run copper anymore and NEVER get them wet. European cars can use Bosch if oem, or ngk/denso ( like european built Tbirds could have Motorcraft branded NGK or Denso mixed in same engine).
But still swapping ign parts between cyl is valid and quick and dirty diag.
As for igition parts, caps, rotors SOME coils/cops just hit local NAPA and buy Echlin or Belden parts. One caviate NISSAN COILS bastards will set coil primary codes. If you can tune them out fine if no misfires but I HATE Nissan coil pickiness.
And Motorcraft has opened up to making parts for all brands under Omnicraft header, and I am curious on thier ability to produce multiple brand lines parts. But i am hopefull as Motorcraft /AC Delco tend to cost more but quality beats other brands .
Most dont know but Echlin used to make all of Accel ignition parts, back when they were top shelf, then over years quality failed, now that prestolite has them back seems parts are getting back up in quality.
