Removing Injector Diffusers - Tips
 

I pulled my injectors while chasing down a fuel leak, and decided to remove the diffusers to replace the seals and o-rings. I was super nervous to do this after reading multiple stories of injector diffusers breaking during removal, so I thought I would share what worked for me. The best advice I can give is to take your time and be very gentle.

Secondary Diffusers

These were much easier than the primaries. I used a small pick to remove the silicone(?) injector grommet that fits on top of the diffuser (P/N NF01-13-257A), and at that point the diffusers were essentially loose and I was able to remove them easily with needle nose pliers. Even if they weren’t loose, I would imagine grabbing the top diffuser flange with pliers and gently working them out wouldn’t have been a problem. Some silicone spray would probably be helpful if they are really stuck in there.

The lower diffuser o-ring P/N is 9954-10-1252, and if you need to replace the secondary diffusers themselves the P/N is N3A1-13-C60.

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Primary Diffusers

I definitely struggled with these at first. I initially thought they had a separate injector grommet on top and I was attempting to remove these first just like the secondaries, but it turns out the grommet/seal is part of the diffuser.

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After spraying a little silicon lubricant down the holes, I discovered that a paint can opener was the perfect tool to “hook” the underside of the upper portion of the diffuser. I very gently pried on one side of the diffuser, then the other, and after a couple of minutes they came loose and I was able to pull them out.

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One thing that was not obvious to me at first was that the injector hole in the engine block extends down farther than the upper portion of the diffuser. In other words, if you stick your hook too far down the hole you will be prying on the block and not the diffuser.

If you need to replace the primary diffusers, the P/N is N3A2-13-C61. These do not have a lower o-ring like the secondaries, and the seal on top that is part of the diffuser is what contacts the fuel rail. You will need two Fuel Injector Grommets (P/N N3A1-13-257), but these fit on the fuel rail itself (this photo is not mine):

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This is probably nothing new to many of you, but if you're like me and have never pulled your injectors or diffusers before I hope this is helpful.

In general, I leave them alone unless I'm rebuilding an engine. Over time I've found that they are fine if you leave them be. As soon as you touch them they can break.

The grommets that seal the bottom of the fuel rails to the engine can be replaced fairly easily without messing with the diffusers.

This is a SUPER easy job with the engine apart. Just push on them from below with your finger and they pop out or break.

Really there would need to be a specific reason to do this in the car. Don't just do it because you're in there, even with this technique it's very possible that they will just crumble on you and you're trying to fish out broken plastic from inside the engine. The only way I've seen to do that is a powerful shop vac with a sheer stocking or something over the end so you can see when you get the part out. If an engine eats that hard plastic that can do some major damage.

Dale

Spray them with wd40 or some other lubricant and use a strong pick to pull them straight up. The reason they get stuck is the orings get hard. If they break get a strong shop vac and suck out whatever fell in. Make sure you empty it first so you can easily see if you got everything. I have yet to come across a situation where a piece broken off and I wasn't able to vacuum it out.

Just as Chris stated.
My engine was rebuilt back in 1999. In Jan. 2021 I replace my complete fuel system.
The stock primary diffusers came out without any problems. A little WD40 and a hooked coat hanger end worked so easily.

If they break, get a couple different size hoses (one smaller than the other) and a lot of ducktape. Stage them in a step down configuration and stick them down the intake runner to suck up the pieces.​​​​​​​​​​​​​​If they didn't crumble and are in pieces you can put them together like a puzzle to make sure you removed all of them.​​​​​​​

I can see reason to pull the secondaries out since they have an o-ring. But why remove the primaries if you’re not replacing an o-ring on them? Seems like unnecessary risk. This is a very good right up though. Thank you.

I typically do the opposite. I leave the secondaries in there and just replace the o-ring/grommet that sits on top. The rubber seal is part of the Primary diffusers so I always replace those because the rubber is always hard and flattened out so it will pose as a possible leak point. You can see in the pictures above where the rubber is broken off one of the primaries because it was so brittle.

So you replace the entire primary? I’ll try to take a look at them before I remove them but I’d rather not remove them if there’s the chance of having to extract broken bits. That is a good point though.

I have yet to break one but that's not to say it won't happen. Just be super careful with them. I drop a little bit of WD-40 on them first, (don't spray a ton) then try twisting slightly after it works its way in. Once they twist they usually come out fairly easily. I explain my reasoning here at the 22:40 minute in this video. I show the secondaries being left in the lower intake too and just replacing the top grommets/seals.