"Decapping" factory fuel injectors

This is the cheap way of getting more fuel into your engine that is required when making more power than the factory fuel injectors can support.

"Decapping" fuel injectors is pretty much what it sounds like. You are removing the pintle cap to increase flow through the injector. The factory uses pintle caps to restrict the flow of injectors and to help flow match injectors. By removing the pintle caps you are unrestricting the flow through the injector. Because of this modification their may be flow variance between injectors. This is due to the fact that before the stock pintle cap was the fuel flow equalizer through the fuel injector from the factory and now after decapping the fuel injector, the only thing that is now making the injectors flow the same is the factory machining tolerances within the injector. Because of this, it is HIGHLY RECOMMENDED that you send your fuel injectors out for flow testing, and also that you keep a eye on your spark plugs to see how the AFR's are looking cylinder to cylinder. If you have a spark plug that looks like its noticeably richer or leaner than other cylinders, I recommend modifying another factory stock fuel injector of the same flow rate and part number, having it flow tested, swapping the problem injector out and testing again.

then sending them out to eric, info below

Ok onto how to do this modification. Heres a video for the visual learning people out there:

sloppy mechanics how to video

Dale Follett's video

Now for what cant be seen in the video. In this photo you can see the dark ring inside the black fuel injector O-ring retainer. This is the friction weld that holds the pintle cap onto the injector. This is what needs to be ground off.

So heres a visual reference of the pintle cap half off the injector

And then heres the pintle cap completely off the fuel injector

The part you see in the middle of the completely decapped fuel injector is the pintle. DO NOT TOUCH THIS WITH A GRINDER, YOU WILL RUIN THE INJECTOR! You just want to grind off the friction weld that holds the pintle cap on and nothing more.

So that is how you modify your fuel injectors to flow more fuel, now heres the proof this works.

I (Dale Follett) Did this to a set of Delphi 25lb/hr fuel injectors from a junkyard LM7 5.3L. The injector part number is 25320288. I modified 8 of them and then sent one out for flow testing to witchhunter.com so I would have data to use in my megasquirt's tune. Here are the returned test results:

So from these test results, we can see at 43.5psi the fuel injector flowed 583cc/min. Using witchhunter.com 's online calculator I converted that to LB/HR. 583cc/min = 55.4 LB/HR of fuel flow at 43.5psi. Now for us LS engine guys, our factory fuel rail pressure is 58psi, so I used witchhunter.com 's calculator again to convert that flow number to 58psi and came back with the flow number of 64 LB/HR at 58psi of fuel pressure. This means this particular modified fuel injector flows 256% more fuel than it did in factory form. Now this flow number IS NOT FOR ALL FUEL INJECTORS. I HIGHLY recommend sending all of your fuel injectors out for flow testing to see where you stand with your modified fuel injectors. As I stated, I just flow tested one and have been keeping a eye on my spark plugs, with good results.

EDIT 2-26-17, Just send all your fuel injectors out for flow testing so you know where you stand with your injectors. I've been getting a few injectors that are frozen up or fail a leak check from the junkyard, so for peace of mind and so you dont wound a engine, just send all your injectors out for flow testing or build a rig to flow test them from home.

I am currently running these particular modified fuel injectors in my pontiac firebird. The setup currently as of 7-18-16 consists of a BONE STOCK junkyard 4.8L LS, 4L80E transmission with a factory unknown vehicle junkyard 1700rpm stall converter and 2.73 rear axle gears. The vehicle is twin turbocharged using 2 different sized turbochargers from the junkyard. The turbo kit is a little large for this engine and takes a while for it to spool up. So far this setup on 13psi has ran 14.11 at 111mph at Beaver Springs Raceway. I have sense upped the boost pressure to 16.5psi. At 16.5psi of boost pressure, at 6200rpm my fuel injector duty cycle is 66.2%. Heres a graph:

I have a little work to do to the tune, but I am commanding a 10.8 AFR and the injectors so far are easily keeping up with that, which a factory 25lb/hr fuel injector would have NEVER done. This car also has been driven over 700 miles with next to no issues. I did have 1 fuel injector fail at around 650 miles due to dirt getting into the fuel injector. This is due to the fact the firebird has no fuel filter. It was caught by keeping a eye on the spark plugs, and thus is why it is important to keep a eye on your spark plugs while you are getting your setup dialed in with these fuel injectors and whenever you notice the engine not running correctly, mine was sputtering. I swapped it out with another bench ground fuel injector and its been running fine ever sense, and see's boost every time its out.

Now there are others on the Sloppy mechanics facebook page that are decapping the 5.3L denso flex fuel injectors. At this time I am currently waiting on a reply for the part number of said fuel injectors being used in this testing. But Joseph Houze has posted a video that can be found here:

The outer two injectors in this video are the modified 5.3L denso flex fuel injectors, the inner two injectors are deka 80's. They almost flow the same. Its believed the 5.3L denso flex fuel injectors flow 78lb/hr, but none have been sent out for flow testing to verify that number to the best of my knowledge.

And as always the disclaimer.

This modification is DO AT YOUR OWN RISK. I (Dale Follett) will NOT be held responsible or liable for any damage done to your vehicle due to the results of this modification.

Credit: Cory Dunlap for the last 2 injector photos, and Joseph Houze for letting me share his injector flow video.

For any more information on this style of modification, GM part number vs average decapped flow rating or any other questions please visit GM Uncapped Injectors facebook page found here: https://www.facebook.com/groups/285371198529480/

I took some photos of this myself, after decapping a set on my own from dales instructions. also i will be linking a video of me doing the same!

Matt's Decapped Fuel injector flow testing results video.