How-To: Replace Fuel Injectors

midwestdenaliguy · August 5, 2020

I ran into a rough start/misfire issue last year and ended up replacing my fuel injectors. I started a thread when I was troubleshooting it because I could not find any complete instructions, write-ups, how-to's, etc. on how to replace the injectors in our DI engines. In the thread I mentioned that I would post a how-to in this forum, appreciate everyone who chimed in to help. I try to give back because I have saved countless time and money learning from a lot of you. This took longer to post than I wanted thanks to having my firstborn (poor guy gets blamed for a lot of stuff - mainly farts), but finally got around to it! Below is a step by step guide on how to replace the fuel injectors on a 6.2L (L86) direct injection engine for the K2XX platform. If you have a different engine/platform you'll want to do your own research to ensure the replacement is done properly.

DISCLAIMER: I consider myself handy and have the right tools to do a lot of jobs on my vehicles - but I am not a certified technician. I spend a LOT of time researching and asking questions before I do any repairs. This is the result of online research, talking to people in this forum, and talking to technicians that I personally know. I also grew up fixing cars with my family - who are engineers with GM. If you do not have confidence in replacing fuel lines and/or opening up the intake portion of your engine then you should let a professional do this work.

You will need the following tools:

- Torque wrench for both ft/lb and in/lb specs.

- Socket set with extensions and a swivel adapter if you have one. There are some tight spots that you have to get to for bolts and a swivel adapter made it much easier.

- Trim removal kit, not critical but makes it much easier. This really helped with a set of push on clips for a wiring harness that's behind the intake manifold.

- MAF and throttle body cleaner if you want to clean your intake while it's apart, not critical though.

- Blue loctite for high pressure fuel pipe fittings.

- C-shaped fuel line removal tool, not required but greatly helps in quick removal of low pressure fuel pipe (can borrow a kit from an auto parts store).

You will need the following parts (again this is for the 6.2L L86 engine - yours could be different if you have a different engine/platform). GM says you must replace the fuel pipes after removing them, they may leak fuel if reinstalling old fuel pipes:

- Fuel injectors part # 12668393

- Intermediate #1 Fuel Pipe (crossrail pipe that connects both fuel rails) part # 12677002

- Intermediate #2 Fuel Pipe (from high pressure fuel pump to crossrail fuel pipe) part # 12677004

- Fuel feed pipe w/check valve (connects low pressure fuel line to high pressure fuel pump) part # 12618338

- Intake Manifold Gaskets (8) part # 12626354 (It's highly recommended to replace these, even if they look good. At ~$2 each it's cheap insurance.)

Steps to replace fuel injectors (pics/diagrams attached to provide visual aid). Carefully remove everything in these steps as they are tied to the intake of your engine - don't rush it. Clean off top of engine before starting removal as debris can seriously damage your engine if it falls into the intake:

1. With truck off, pull fuel pump fuse from main fuse box in engine bay (fuse #21).

2. Start the truck and let it run until it stalls out (can happen within a few seconds or take as much as 30 seconds). This ensures fuel is run out of the fuel lines and the fuel pumps/lines have no pressure. If you do not do this step the high pressure lines you will be removing can spray fuel everywhere and cause damage/injury.

3. After truck stalls out, shut it off and unhook the battery so the truck has no power.

4. Remove resonator box/intake tube going into throttle body. 2 clamps are loosened - 1 at the throttle bottle and 1 at air box. Disconnect MAF sensor electrical connection on intake tube by air box. Disconnect both driver and passenger clean-side fittings (removed by pressing on the light gray plastic strip and squeezing it together and pulling the fitting off the barb). Resonator box is now free to pull out of engine bay. Lots of videos on Youtube show how to do this is you're still unsure.

5. Disconnect PCV hose fitting next to throttle body (same style fitting as clean-side fittings on resonator box).

6. Remove throttle body (1 electrical connection and 4 bolts).

7. Unclip electrical wiring harnesses that run along both sides of the intake manifold (3 plastic push clips on each side). Trim removal tool can be helpful here, but mine pulled out fairly easily by hand.

8. Remove 5 intake manifold bolts on each side (10 total). They are finicky to get completely out as they have a little catch ring on them to not easily fall out of the intake manifold. If you can't wiggle it completely out, just make sure it's not fastened to the engine block any more and leave them in the manifold - you can still remove the manifold with them loosely in it.

9. This part was a pain - but slightly lift up intake manifold and pull toward you as much as you can. This will give you *some* room, not much, to reach behind the intake manifold and pull out 4 more of the push style clips holding the electrical wiring harness to the back of the intake manifold. It's tight because the manifold is right up against the firewall. I used a trim removal tool to get leverage on the clips and pull them out. It'll be a pain to remove some of them, don't be afraid to give it some muscle. (See pic below showing where clips are located)

10. With the bolts and clips all removed you can now lift the manifold off the top of the engine. Remove the black foam pad under the manifold to expose the fuel lines/rails. Be careful and try not to drop debris in the intake openings. Now is a good time to clean your intake manifold and replace the gaskets.

11. Tape off or put clean rags in your intake openings to prevent anything from falling in while you remove the fuel lines, rails, and injectors.

12. Unplug the electrical connections to the fuel rails (on the ends by the firewall).

13. Remove the 3 fuel lines from the high pressure fuel pump and 2 fuel rails (see pic below for fuel line/rail set up on the 6.2L L86). I found it easier to remove the fuel pipes first while the rails are still installed (gives you more torque if you need it). The 2 high pressure fuel pipes should have loctite on them, but they did break loose fairly easily. There is 1 bolt holding in the crossrail fuel pipe. I borrowed a fuel line removal kit from Autozone for the low pressure fuel line, it clicks into barb fittings. The low pressure fuel line (rests just above the driver side fuel rail and clips into the high pressure fuel pump) has a special fitting on each side of the pipe that is a pain to release without a special tool. The tool itself is a plastic 'c' shaped clip that goes around the fuel line and pushes into the pipe end, releasing it. There are 4 bolts holding in each fuel rail (8 total).

14. Slowly pull out each fuel rail, I had to firmly wiggle them but they came out by hand.

15. Look in each injector port and make sure there's no debris/crap in there. If you see anything try using a vacuum hose to suck it out or use something else to carefully swab out any debris. You want the injector ports clean so the teflon gaskets on the injectors seat properly in the port.

16. Swap your old injectors with the new injectors on the fuel rails. There's a metal clip on each injector holding it against the rail that can be a pain to take off, but you need them so don't damage them. I used a flathead screwdriver to pry them off, they clipped back on easily.

17. Reverse these steps to put it all back together. Make sure you torque all bolts and pipe fittings to spec or else you risk damage and/or leaks. Below is a pic of the torque specs, I highlighted the ones you need.

18. Start truck up and pray you did everything correctly.

19. If you drink, crack open a cold beer and take pride in your work as well as saving big bucks. If you don't drink, crack open a cold apple juice and take pride in your work as well as saving big bucks.

Edited August 10, 2020 by midwestdenaliguy

15Yukon · August 6, 2020

Did you need to replace the intake manifold gaskets or did you re-use them?

midwestdenaliguy · August 6, 2020

48 minutes ago, 15Yukon said:

Did you need to replace the intake manifold gaskets or did you re-use them?

I ordered the gaskets ahead of time and replaced them just in case they were in bad shape. I wanted to get it all done in one shot and not wait for something to arrive if I had to replace them. They looked good though, ~75-80k miles on engine at the time. Still replaced them since I had the new ones and they aren't that expensive. Cheap insurance I guess.

This is a good call out, I'll add it to the original post.

15Yukon · August 6, 2020

Any idea where I could find part numbers for the 5.3l? Im pretty sure its all the same for the fuel lines and intake mani gaskets but I want to be sure before ordering.

davester · August 6, 2020

I wouldn't reuse an intake manifold gasket unless it looked perfect AND GM explicit has written it is reusable, as even a small leak with a gasket causes engine problems...

newdude · August 6, 2020

1 hour ago, 15Yukon said:

Any idea where I could find part numbers for the 5.3l? Im pretty sure its all the same for the fuel lines and intake mani gaskets but I want to be sure before ordering.

Intake gaskets are the only for sure same part. The fuel feed pipes can change based on engine/trans combo.

What year is your 5.3 whatever you drive?

midwestdenaliguy · August 7, 2020

9 hours ago, 15Yukon said:

Any idea where I could find part numbers for the 5.3l? Im pretty sure its all the same for the fuel lines and intake mani gaskets but I want to be sure before ordering.

I'm a believer in always using your vin number to find the right parts. You can call a dealership parts department and ask for the part numbers you need (some may or may not give them to you depending on how nice they are). You can also search by vin number on multiple OEM GM parts websites, like www.gmpartsdirect.com, and find the part numbers you need. Then do some shopping on multiple sites for the best price.

FYI - OEM injectors are notorious for being on back order. I went through a seller on eBay that has a great reputation and match flows new OEM injectors. Has a great price too. This is the link to what I bought for my L86 (6.2L) engine, you can reach out to the seller with the last 8 digits of your vin and he will confirm which ones you'll need. I've been driving with mine installed for ~35k miles and have had zero issues. https://www.ebay.com/itm/Set-of-8-BRAND-NEW-OEM-Fuel-Injectors-Chevy-GMC-6-2L-2014-17-12668393/201906630442?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

9 hours ago, davester said:

I wouldn't reuse an intake manifold gasket unless it looked perfect AND GM explicit has written it is reusable, as even a small leak with a gasket causes engine problems...

Good advice, I'll reword the original post to strongly encourage it.

Edited August 7, 2020 by midwestdenaliguy

15Yukon · August 7, 2020

18 hours ago, newdude said:

Intake gaskets are the only for sure same part. The fuel feed pipes can change based on engine/trans combo.

What year is your 5.3 whatever you drive?

2015 Yukon, 5.3, cant find any info on those pipes on any of the GM websites

Edited August 7, 2020 by 15Yukon

newdude · August 7, 2020

2 minutes ago, 15Yukon said:

2015 Yukon, 5.3

So your injectors are 12698484, the pipes are 12703596, 12677004 and 12677002.

15Yukon · August 7, 2020

Thanks newdude, injectors are 12268390 from what ive searched, VIN: C

Edited August 7, 2020 by 15Yukon

Eddie 70 · August 10, 2020

Thanks for the detailed write up. Hopefully I never need it but I can search it up if needed.

midwestdenaliguy · August 10, 2020

2 hours ago, Eddie 70 said:

Thanks for the detailed write up. Hopefully I never need it but I can search it up if needed.

No problem. When I started my research I was surprised to see so many people dealing with misfires, rough starts, etc. all due to bad injectors. Warranty repairs were all over the place...some dealerships only replacing the injector(s) where the code was coming from, while others had all 8 replaced. Those out of warranty were quoted an insane amount for the repairs. If people find themselves in the unfortunate situation where this is needing to be done, hopefully this helps decide if they want to repair it themselves.