I have a 2004 Honda Accord EX Sedan with a 2.4L I-4 with California emissions and 250k miles on it. I desperately need to replace my fuel injectors but the price is steep!

Can someone explain to me what the difference in the fuel injectors is, between the version for standarf/federal emissions, and California emissions vehicles? At this moment, I've been looking for info on them but can't find much... and honestly, they appear to be the same injector, just priced differently.

I know the difference between emissions types, but I want to know the difference between the injectors for those types of emissions. Honda gave me two different part numbers for them, but declined to detail what the difference was - other than $100 per injector.

Can someone shed some light? Thanks!!

Edit: As far as I can tell, the numbers stamped on the injectors are as follows: RH28 AAZT Z 90 degrees from that, on the side of the injector, is just "T" which I'm assuming means it's a model T injector - the part numbers from Honda are 16450RADL61 for the CA emissions injector, and 16450RAAA01 for the Federal emissions injector.

Honda and Rock Auto both list a separate injector for the SULEV CA emissions engine, Autozone and everyone else has only one, the model T.

Update: I've replaced the injectors with a standard "T" model, so far no issues that I can tell, and my car has lost 80% of its misfires... I still have an exhaust leak to fix and after that I should be able to tell if the emissions are good or not. Thanks all for the help!

  • Welcome to Stack Exchange. Can you provide the make/model and year of the vehicle? Commented Mar 3, 2016 at 17:40
  • first line of the post... Commented Mar 3, 2016 at 17:45
  • 1
    That's excellent. Apologies. I'll get me glasses out. Commented Mar 3, 2016 at 17:52
  • I am completely not sure of the answer, but I can't resist myself from making a guess. I think the regular or standard/federal emission fuel injectors would be sending in a little more fuel than the California emission fuel injectors. I have lived in California for about four months and know the traffic levels and the population that lives in and around the bay areas. By keeping the emission levels to a minimum level where ever possible, California parking lots have reserved spots for compact cars, hybrid, electric so that they can reduce the pollution.
    – kasey
    Commented Mar 3, 2016 at 18:21
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    @kasey. Not saying you're wrong, but I would have thought the fuel map in the ECU could be adjusted to put less/more fuel in if that was all it needed.
    – HandyHowie
    Commented Mar 3, 2016 at 22:28

2 Answers 2


The most reliable way to tell if two injectors are interchangeable is to determine how much fuel they can flow in a given amount of time. The close the two flow rates are, the more compatible they will be.

In an ideal world you could bench-test them with a setup similar to Jafro's.

The difference in fuel trims before and after injector replacement is another way to tell if the two models were different or identical - there would be no change in fuel trims if the two models were for functionally-identical injectors.


For the 95 Celica 5FSE, there is an extra O ring (a second ring on the head side of CA injector, more like a squarish cross section grommet) on an otherwise identical LOOKING injector. Square section rings usually used to improve sealing over plain round section types.

Doubt there is a fuel flow difference, the CA emissions (I believe) of the era added some air supply to lower combustion temps & increase O2 to alter NOx ? I'd have to look that up

Compare pics of the parts 48state 23209-74100
CA 23209-74140.

My first guess is it has something to do with a problem arising from the air injector hose (leading from idle air control into head ) or to just control the air flow path in the head

Ive seen ring kits with the extra rings, instructing " install if present on old part "

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