Substitutable Parts--or right v. wrong?!


I need to get to the shop and do SOMEthing re my lame Legacy,

and would like to have some sense of the community re this parts issue,

before I have to argue/plead my case (about possibly redressing the

installation of a wrong part), and maybe limp away to another shop.

(And I see that the December “R&R #1 injector” cost me $118; part, $170.)

After much Googling & e-mailing suppliers, makers, I have learned that

to the best of apparent knowledge, the fuel injectors that came with

my, and are spec’d for my '91 Legacy non-turbo auto.trans. wagon

look like Standard Motor Part FJ446 (see link below–good images);

and those for a MANUAL or Turbo look like FJ386 (or FJ521).

A Subaru dealer had a sample of the one for automatic, which I saw

(#16611AA090 vs. -120 for manual).

But the shop, in December, installed an SMP FJ521, which SMP claim is

for the Turbo, and which in any case matches in appearance those

for manual trans.–having a blunt & recessed injector tip, and a much

wider fuel filter window (side opening). ?? Subsequent to the December repair,

there were a few instances where I heard a tapping noise from the engine,

varying w/engine speed; never present prior. Could that be related to

the new, wrong-part injector (also O2 & knock sensors) … ?!

NB: The distinction in appearance of the auto vs. man.(&turbo) '91 injectors

is consistent as noted. (RockAuto’s pics are great to compare–see:



FJ446 is exactly like the Sub. part (heck, maybe SMP makes if for Sub).

Thanks much for some insight on this!



Yes, the different part could be the casue of the noise. The spray patterns and densities are very different for the two, the OEM one having been designed for higher mechanical compression at lower RPMs without preignition and the replacement they used having been designed for lower mechanical compression at low RPMs and to provide sufficient fuel properly dispersed for higher “boosted” compression at high RPMs when the turbo kicks in.

In short, the injector designed for the turbocharged engine conditions could be causing preignition. I suspect your non turbocharged engine has higher compression until the turbo kicks in.


Thanks for this insight; it’s the sort of thing I guessed might be the case.

For the record, it’s rather amazing what sorts of conflicting / inconsistent recommendations one can find at the various
parts sites. E.g., one site has a maker distinguishing my model-year “1991” on production dates (pre-May vs. later),
several make no discrimination on transmission or turbo/non-turbo!? And yet if one goes to the actual part-MAKER’s
site, there might be such a distinction. (And the maker itself might have mistaken info–pretty sure e.g., that Standard
Motor Parts got their auto/man rec’s swapped; they’re looking into that.)

Holy Haphazards, Batman!!!


Yes Robin, that blond is…Oh, nevermind.

Usually the absolute best way to get as accurate as possible information is through the dealer using the VIN number. Everything other source is second and third hand.

Not everyone is aware of the potential issues involved with spray pattern, density, and even release point. Any good ASE tech should be, and even some dummies like me are, but the reality is that there are many out there that think any injector that physically fits and will respond to the pulse to open will work fine. And there are many sho don;t care…they put in whatever part they have handy.