OBS Resurrection Injectors (Part 8)

OBS Resurrection Injectors (Part 8)

table of contents

The OBS Restoration project just keeps moving right along now into the eighth step of the build on our F350 Ford truck. At this point, it’s time to silence some naysayers about the potential of that old 7.3L Power Stroke and make a respectable horsepower number. The old school HEUI injection system is getting an upgrade with modified Hybrid injectors from Full Force Diesel of Murfreesboro, TN in hopes of slamming 400+ horsepower down at the tires.


With no real signs of failing injectors, like a poor idle or haze at idle, with 230,000 miles the factory injectors have definitely paid their dues. Full Force Diesel has been specializing in the 7.3L platform for over a decade and has fine tuned their options for upgraded performance injectors for the HEUI (Hydraulic Electronic Unit Injector) system. The factory injectors in the 94-97 7.3L was a single shot 90cc AA-code, which means it has one injection event per combustion cycle and can move a total of 90cc of fuel in that time. In an OBS truck, you are limited to around a 70-80hp max increase with stock injectors before they just can’t get anymore fuel into the cylinder.


Increasing the cc’s of fuel delivery and changing the nozzle sizes to achieve more power and performance to meet your specific power and drivability goals leaves lots of options on the table. Full Force can increase the flow rate up to 450 cc's, but that’s way more than you’d ever need in a daily driving and towing application.  On the nozzle side of things, the larger the nozzle allows all that fuel to empty faster, making for more precise timing of the injection event. For a tow rig wanting more power you’ll need more CC’s and maybe a mild nozzle upgrade.


For this build, since we already had the intercooler and upgraded turbocharger and a 400+ HP goal, Stage 3 205/30 Hybrids were chosen. The hybrid injector design uses considerably less high pressure oil than a big A-code injector, meaning the engine can maintain higher injector control pressures on a stock high pressure oil pump. By utilizing the smaller 30% nozzle with the higher flow rate, the right tuning means more fuel volume at the nozzle for better atomization. Improved atomization means more power with cooler EGT's and less smoke. Both ideal outcomes when towing. The 205/30 injector is going to max out around 425-450hp, which is going to be more than enough for this basically stock engine.



01 –Perfecting their signature fuel injectors to produce some of the cleanest running and most efficient modified injectors, Full Force Diesels Stage 3 205/30 Hybrid is a great option for this build.

02 – While an injector swap may sound like a daunting and overwhelming task, if you’ve ever done a glow plug job on your end, injectors don’t add to many extra steps and can still be accomplished in a few hours’ time with the right tools and knowledge.

03 – With the valve covers removed from the engine, you’ll get your first real look at the HEUI injectors that power the 7.3L engine. Pulling the injectors requires just disconnecting the electrical connector and the removal of the lower hold down bolt. The injector hold down can then be slid upwards to clear the top hold down bolt and a small pry bar to pop it up and out of the injector cup bore.

04 - With the injectors removed from their bores, you’ll see and hear engine oil from the oil rails draining down into the cylinders, which will need to be evacuated and cleared upon reassembly. You’ll also notice the glow plugs which will need to be removed at this point as well.

05 – The entire driver side bank of injectors is out and on the bench. While the truck was still running fine, at 230,000 miles they are definitely tired and should be showing signs of wear inside which can affect performance and efficiency. It is also common at higher mileage that the O-rings can leak causing poor running conditions and hard starting as the high pressure oil system can’t build pressure like it should.

06 – Our new Full Force 205cc Hybrid injectors come ready to install with new O-rings and the copper washer to seal it in the injector cup. Since we’re upping the volume of fuel the injector can move from that stock 90cc to 205cc, we also opted to upgrade to a 30% over nozzle, which can help that fuel exit quicker.

07 – The passenger side will take a little more time due to some of the space constraints in the engine bay, but you follow the same process. This is also a great time to check your valve cover gasket/harness as they are prone to fail at the connectors, so the injectors and glow plugs may not receive the power and signals they should.

08 – When the new injectors are reinstalled into their cups, the injector hold down bolt will need to be reinstalled and it is important to torque these to the proper spec. If that bolt were to come loose, the combustion pressure could push the injector back up out of the cylinder head and lead to some major issues.

09 – With the injectors torqued down and the glow plugs removed, we used a small vacuum pump to suck as much oil up and out of the cylinders as possible. Then, the valve covers can be slid over and held in place with just a couple bolts so the engine can be barred over by hand off the damper bolt. Cycling the engine over a few times will push any left over out through the glow plug holes.

10 – With the oil evacuated from the cylinders the glow plugs can be installed, valve cover harnesses connected to the plugs and injectors, and the valve covers torqued down. At that point, it is a good idea to fill your high pressure oil reservoir through the small port directly on top of it. This will help refill the oil rails quicker while cranking, hopefully leading to an easier first start-up.