Replacing NA8 Miata Fuel Injectors

"mXxxxXm24 /O/ /O/" (mxxxxxm24)
06/17/2019 at 19:15 • Filed to: Arisu, Miata, Miatafications, Rough Idle, NA8

Arisu: when she was clean a few weeks ago.

I have been tuning up my 130,000 mile, original NA8 engine one step at a time. Recently I’ve replaced the air filter with a drop in high flow green filter, oil/oil filter change, plugs and replaced the plug wires and coil pack with individual coils. Today I replaced the original injectors with some cleaned and flow tested oem injectors with new rubber gaskets.

I had been dealing with an intermittent rough idle and rough running engine. I had done a number of things over the years in trying to trouble shoot, but it was still there nagging me like a nagger would. It was recently suggested to me that it could be leaky or dirty injectors. I have never messed with injectors before, but was told it was simple. Remove 3 bolts and pop out 4 injectors and done.

Engine bay before any removal.

After looking around there wasn’t much in the way of specific information with what needed to be removed in order to access the fuel rail/injectors on the NA8 engine. Some people choose to completely remove the fuel rail from the fuel lines. I did not, but it made for a tighter wrenching space. As I saw it, I only needed to remove a few things before I could start removing the fuel rail: one clip, one cable tie, one pcv hose, and in hindsight 4 clips on the injectors.

The clip you’ll want to remove.

Before working on the fuel system though: remove the fuel pump relay in your fuse box, crank your ignition for 5 seconds, and remove your gas cap. Also remove the negative battery cable. Now after you have removed the aforementioned things (clip, cable tie, pcv hose, 4 injector clips) in the way of the fuel rail, you can take a 12mm socket and undo the 3 bolts that hold the fuel rail in. DO NOT take the bolts all the way out yet. Be very careful to do one at a time keeping a hold on each spacer between the fuel rail and the engine block. They will fall right out if you remove the bolts all the way. Next remove the injectors by wiggling them out as best you can. Then use a q-tip to clean the injector seats on the engine.

You can see the injector seats are reasonably clean here.

After that you can carefully put in your new injectors. I will note here that I reused the original injector seat spacer gasket (yes, I just made this name up). The ones that came with my kit were supposed to be oem, but did not look the same or fit snuggly onto the injector. It would have been almost impossible to install the new ones without them falling off into the engine bay. So I cleaned the originals up and put them on the injectors and then one by one seated them on the engine.

New injectors in and loosely seated. Needs to be seated and bolted back in.

Next put the fuel rail carefully onto each injector. Firmly pressing each one in place. You might want to use vaseline to reduce the risk of damaging the o rings. It takes some persuasion, but you’ll be able to tell when they are on. At this time make sure they are seated on the engine and the fuel rail and carefully put the spacers back in one at a time securing each one with a loosely attached bolt as you go. After that just put everything back together in reverse order and you can start her up!

A job well done. No leaks!

You might have noticed I was very emphatic about not dropping things in your engine bay. Well... that’s because I may have dropped a 12mm socket into the engine bay. And it may or may not still be there. I could not find it for the life of me. I am worried about what will happen as a result. Oppo? Will it be ok?

DISCUSSION (18)

CaptDale - is secretly British > mXxxxXm24 /O/ /O/
06/17/2019 at 19:27

Very pretty car

mXxxxXm24 /O/ /O/ > CaptDale - is secretly British
06/17/2019 at 19:32

Thanks dude! She’s far from perfect and could use lots of restoration work, but she cleans up pretty nicely!

CaptDale - is secretly British > mXxxxXm24 /O/ /O/
06/17/2019 at 19:35

You’re welcome. Not all cars are perfect but looks like you take car of her.

mXxxxXm24 /O/ /O/ > CaptDale - is secretly British
06/17/2019 at 19:40

I try! She’s my only car and want to keep her for ever if I can :)

CaptDale - is secretly British > mXxxxXm24 /O/ /O/
06/17/2019 at 19:42

I definatley understand that feeling.

Wrong Wheel Drive (41%) > mXxxxXm24 /O/ /O/
06/17/2019 at 19:59

Hmm, wondering if this is the same on my NB2? If nothing else is in the way from the VVT it should be the same at least. I’m thinking a faulty injector is causing my CEL. New coils made my car run much better consistently, but its still flashing the light occasionally on a cold start and idles a little rough until it warms up. Not enough of a worry to really bother me now that it runs much better on the new coils. But injectors were the next thing to try before assuming a burnt valve or something else dumb.

Where did you buy your injectors from?

mXxxxXm24 /O/ /O/ > Wrong Wheel Drive (41%)
06/17/2019 at 20:11

I am unsure, but prob similar enough. Treasure Coast Miata sells them. They are flow tested. Mine had results of 260cc 261cc 260cc and 253cc with good spray patterns. The variance bothered me at first but I got over it lol. Was told it wouldn’t make a difference.

mXxxxXm24 /O/ /O/ > Wrong Wheel Drive (41%)
06/17/2019 at 20:12

You could always have yours serviced since you have a second car. Probably cheaper

gettingoldercarguy > mXxxxXm24 /O/ /O/
06/17/2019 at 21:20

Are your valves hydraulic lash or mechanical?

TheRealBicycleBuck > mXxxxXm24 /O/ /O/
06/17/2019 at 21:32

If it were a 10mm, it would be gone forever. A 12mm should show up sometime soon.

mXxxxXm24 /O/ /O/ > gettingoldercarguy
06/17/2019 at 21:55

I believe hydraulic, but I’m not sure. Please explain the difference if you could :)

mXxxxXm24 /O/ /O/ > TheRealBicycleBuck
06/17/2019 at 21:57

Lol I was thinking that the whole time. I’m the only guy who loses the 12mm dammit.

Wrong Wheel Drive (41%) > mXxxxXm24 /O/ /O/
06/17/2019 at 23:27

Good idea, I like treasure coast Miata. And yeah I guess I could but I hate paying someone to work on my car. I am having a shop fix my broken sway bar bolts but it's because it had to go in for an alignment anyways and it was only $40 for what would have been a pain drilling and tapping and crap. I think the cel issue is intermittent enough to ignore for now. We shall see after two track days in the next two weeks if it becomes a problem lol.

mXxxxXm24 /O/ /O/ > Wrong Wheel Drive (41%)
06/18/2019 at 00:12

I ignored (somewhat) mine for years lol. It’s not like they’d be working on your car. You take the injectors out and give them to an injector cleaning shop. Then as long as they are salvageable they return to you refreshed. I am unsure of cost, but I would have done it if I had a second car and the price was right. I guess you could try to service them yourself. Buy a miatamecha oring kit from eBay and figure out how to clean them properly.

Wrong Wheel Drive (41%) > mXxxxXm24 /O/ /O/
06/18/2019 at 00:51

Ahh that's a great idea if it's not too expensive. I do have the injectors from the old car that are doing nothing anyways. So I wouldn't even have to have the car off the road. Hooray parts car!

gettingoldercarguy > mXxxxXm24 /O/ /O/
06/18/2019 at 05:26

Mechanical is the wrong term, I’m tired all the time with new borns. I almost put French press in my kids sippy cup this morning. For dinner, I almost used a culinary torch to melt bread on top of cheese with a meat patty to the side.

I digress, I meant solid lifter vs hydraulic. I think you have hydraulic which is much lower maintained, doesn’t have maintenance intervals like solid and keeps everything running smoothly.

mXxxxXm24 /O/ /O/ > Wrong Wheel Drive (41%)
06/18/2019 at 09:31

Oh yeah I forgot about your other Miata in this scenario! Even better lol

mXxxxXm24 /O/ /O/ > gettingoldercarguy
06/18/2019 at 09:36

Haha no worries. Yeah they are hydraulic. They tend to tick in miatas. Oil level, age, and viscosity are directly related with the ticking.