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Holley's line of muscle car EFI fuel modules make the process of converting your older vehicle to run on fuel injection simple by incorporating everything you will need, from the Hydramat to the 255 LPH fuel pump and more, onto a stock-style sending unit that fits into the OEM fuel tank like it came from the factory that way. Holley covers a wide range of applications, from Tri-5 Chevrolets through GM G-body cars. Corvettes, Mustangs, GM Squarebody trucks, Jeep CJs, and more have a module that will fit right into the fuel tank. But what if you have an application that doesn't have an option available currently? You can use a Holley Sniper In-Tank Retrofit Fuel Module, which installs simply by drilling and modifying the fuel tank.
Opposed to modifying the factory tank? What then? With 1970s, 1980s and 1990s cars gaining in popularity and the cost of older, more popular models going higher and higher, cars that used to be largely ignored are now being looked at as affordable options. And for a younger market, seeing these older cars for the first time might be the spark of inspiration that they need to pick up a wrench and build something of their own instead of waiting for the day they can bid at an auction for some old metal.
In our case, we have a 1976 Dodge Charger that is being prepared for a conversion to fuel injection down the road and the owner's first goal was to get the fuel system prepared to handle an EFI. While Holley does make an EFI Fuel Tank Module for a 1968-1970 Charger, we knew that the major redesign that the Chrysler B-Body platform underwent in 1971 and the 1975 re-skinning meant that we couldn't bet on that module working. To be safe, we dropped the fuel tank out of the car and test-fit both the 12-384 module for the 1968-1970 Charger and the 12-389 module for 1963-76 Chrysler A-Body (Dart, Duster, etc.) to see if either unit could work in our Charger's tank. The A-body module was immediately ruled out, since the sender is mounted to the top of the fuel tank instead of the side, like a B-Body. The 1968-70 Charger module was close, but we were correct in our assumption that there would be a major design change that would cause a problem, as you can see below:
On the left is a fuel tank and the EFI fuel module for a 1969 Charger, and on the right is the tank and stock fuel module for a 1976 Charger, both showing the passenger side of the tank where the sending unit goes. The 12-384 EFI Fuel Pump Module's pick-up tube and float arm are both angled to the right (forward) from the port. In the 1969 Charger's tank, that's no problem since the sending unit is mounted rearward, leaving plenty of room for the float. But in the 1976 Charger's case, the sending unit is more-or-less straight, float and all. This caused the older design to impact the tank wall and would not allow the unit to fit completely into the tank.
The one thing that we did notice is that the 1968-70 sending unit style and the 1976 sending unit style were close enough in design that if we used the 1976 pickup tube design and float, and combined it with the fuel pump from the EFI Fuel Pump Module, that we would wind up a drop-in-ready sending unit that could handle fuel injection. So...we did just that, with one caveat: we would not be able to incorporate the fuel pressure regulator onto the 1976 sending unit. Not that big of a deal, really...we'd run an external pressure regulator and plumb a return line back into the tank. Follow along to see how we prepared the fuel tank of this 1970s sled for a modern-day fuel system!
That's not pretty, but that's what the fuel tank of a 1976 Dodge Charger looks like after over forty years of use. Honestly, this could've been a lot worse. After draining all of the fuel out and allowing the tank to vent out the remainder of the fumes, we tossed it on the bench and got to work.
Prior to getting started with any customization, we gave the tank a look-over to see if anything needed to be addressed and instantly, the grommet for the fill tube was noted for replacement. It's no shock that after forty-something years, that the outside looked as bad as it did. What did surprise us, however, was how good the inside of the grommet was. The rubber had broken down because at some point in this car's past, the tube had been removed and someone had used red grease, like you'd use for wheel bearings, to help put everything back together. Do not do this! Grease will dry out the rubber over time. Use a good O-ring lubricant instead.
After some much-needed cleaning of the area we were going to be working in, we made the decision as to where we wanted the return line port to be. We wanted to be able to have access to the return line via the sending unit port if needed, so careful measurements were made before the drill was put to use.
With the location marked, we drilled a pilot divot before using a step-bit to open up the hole in the tank for the return port. We then de-burred both edges of the new opening to make sure there was a smooth sealing surface for our Stat-O-Seal gasket washers, and used a vacuum to clean up the shavings both inside and out of the tank.
Here is the total structure for the return port: An Earl's straight -6AN bulkhead with -6AN Stat-O-Seals on each side of the tank and a -6AN nut, which connects to an Earl's -6AN to 5/16ths barbed fitting that has a length of nylon submersible tubing (Dorman p/n 800-074) attached to the end. The tubing needs to terminate low in the fuel level of the tank to keep the fuel from agitating (bubbling). The end of the tube also needs to be pointed away from the pick-up point of the fuel pump to alleviate any feeding issues. Our return port tube runs parallel to the pick-up, so we are okay, and sits a little less than a half-inch from the bottom of the tank. And yes, it's a bit of work to get everything buttoned up!
With the return port buttoned up, our attention turned to the sending unit. We would have to run the positive and negative wire through the top plate of the sending unit, something Chrysler didn't plan for. Instead of using our original sending unit, we bought an aftermarket unit that we wouldn't feel bad about drilling. We just had to make sure that we didn't bother the sending unit's signal wire or stud, and in the case of our aftermarket unit, the grounding spade (the stock Chrysler unit used a grounding strap that connected the external hard fuel line of the sending unit to the hard fuel line of the car). We carefully drilled out our holes, then went back with a larger drill bit to de-burr the edges of the holes front and back. We had to get creative with how we were going to secure the wires in a leak-proof manner, since the sending unit plate is smaller than you would expect. Ultimately, we went with wire bulkhead adapters from a Holley Sniper EFI 225 LPH fuel pump assembly. These bulkhead adapters use a rubber-like insulator that gets smashed down as the nuts are tightened up, sealing around the wire.
The next step was to fit the Hydramat onto the sending unit. After careful measurements to make sure our Hydramat would be in a good position and out of the way in the tank, we determined that we would cut the sending unit's submerged hardline at the first 90-degree bend in the tube. After de-burring and smoothing the cut end, we slipped the pump onto the hard line, clocked the pump and Hydramat to where we wanted it to sit (note the mark on top) and tightened down the 5/16ths stainless hose clamps.
With locking compound on the threads, we tightened the nuts on the bulkhead adapters down on the wires coming through the sending unit. The compound needs at least 24 hours to dry before any fuel is introduced into the system.
The next, crucial step was to take all of the pump assembly and get it into the fuel tank without harming anything, least of all the Hydramat. It's recommended that you put masking tape around the edges of the port to keep any rough edges from tearing the Hydramat as you install the pump.
On the outside, the only giveaways that something has been modified are the two wires from the sending unit and the return port...and maybe the shiny new sending unit. Once this fuel tank is re-installed into the Charger, none of this will be seen unless someone goes out of their way to look for it.
What nobody will get to see in person is the layout of that new sending unit as it's mounted in the tank. The fuel level float clears all of the new components, the Hydramat will always be in the fuel, and the return port tube is off to the side of the Hydramat and low in the fuel level.
While this project required a few hours of assembly and a few days' worth of time to prepare for properly, we're very pleased with the outcome. Just be sure that if you are going to take on a custom job like this, that you do your homework prior to making the first cut or before you drill the first hole. If you have any questions or want to run your idea by one of our technical support staff first, you can reach out to Holley's team of experts at 1-866-464-6553 or email a technician using the Technical Request form, found under the Support tab at www.holley.com.
