EFI Install
Hey, here’s a write-up of my Holley Sniper installation. I’ve had a handful of PM questions, and figured I should write it up. When starting, I also had a ton of questions, having never done much of this work before. I scoured the interweb for build threads and specific info - it is sparse and scattered - so here’s another one…
This is a re-cap, since I’m done with the project. There are numerous starting points and numerous ways to architect the system, so this is specific to one truck and one plan. @abandonedbronco has a good write up on the Bronco forum, and @53deere has info on his build thread as well.
Why did I decide to do EFI? I wanted to get more out of the engine than I could manage with the carburetor - working out lean bogs and rich bogs, start-up in different conditions, swapping around jets, metering rods and springs, tweaking float level, etc is good practice and fun if you have the time, but I wanted a good tune that doesn’t require seasonal changes or regular intervention on my daily driver. Was it worth it? Honestly I’m not sure yet. I went through a lot of money, time and effort. Time will tell if I get consistent, long-lasting performance. The truck does accelerate much better now, with no transitions or hiccups.
My starting point is a 460 big block, standard mechanical fuel pump, factory in-cab fuel tank, American Autowire harness kit, and custom dash gauge cluster. The truck has been modified enough that I’m not shackled to any desire to keep it original.

EFI Choice
I chose the Holley basic Sniper based on price, reduced installation requirements, and familiarity with the brand. The higher-end options didn’t have anything I needed to reach my goals of ‘better’, stable and lasting fuel delivery performance on a naturally aspirated old truck. Upon completion, I would be open to explore other brands, and other Holley offerings, partly because the basic Sniper does not drive external fuel pressure and AFR gauges. I bought it at Summit, which was good, as usual. However if I did it again, I would consider buying it at https://www.efisystempro.com/ because they may offer product support that is better than Holley’s.
Fuel Economy
Driving an F250 4x4 with a 460 engine isn’t a starting point for good MPG. NTL, I’d like higher MPG to extend my range out in the wild. I did an MPG test with my carb a year ago and just re-did it with the Sniper installed. Results = Identical highway MPG between carb and Sniper (which happens to be about 10MPG at 3100 RPM at 68 MPH). No change.
No data yet on city MPG, however since it’s more fun accelerating so I’ve likely lost economy to the lead foot.

What they don’t tell you
Fuel delivery / plumbing / electrical: These are the difficult parts of the project. Holley criminally glosses over all the hard stuff that needs to happen when installing EFI. Bolting on the throttle body and setting up the controller is nothing compared to everything else. More details later, however, understand there is plenty of planning, purchasing and work to be done to a stock classic truck. Total budget including tools was something like 2.5X the cost of the EFI package.
My project was on a daily driver, so I modified, assembled and installed everything in parallel with my existing carburetor setup. When I was ready, I swapped it all over in a couple of weekends. Doing it this way added complexity, cost and time vs. having a truck parked in the garage, but that’s what I needed to do. If I had all the parts and tools at the start, and a parked truck, I think that it would have taken me a few weeks to get through it (while working a full time job and trying to remain a good dad and husband). Add some weeks for learning and planning, and ordering tools and parts, and waiting. The way I did my project took about 10 months from start of planning to completed installation.

A note on Gauges
Because EFI requires water temp info, it uses one water jacket port. If you have only one port, then you cannot run the Holley sender and a second sender to drive your temp gauge. I solved this by using the Holley CAN water temp gauge in my dash cluster - the EFI unit relays the info digitally. I already had an aftermarket 2-1/16” water temp gauge on the cluster, so it fit mechanically. It looks reasonably close to my Stewart Warner gauges with the addition of Holley’s silver bezel ring. However, the backlight is too bright.
I read that one temp sender signal should not be split. I’ve read of people drilling and tapping an additional port to solve the problem as well.
The basic Sniper was limiting because it does not drive the Holley AFR gauge and Fuel Pressure gauge - the higher models do. I already had an AFR gauge on the dash and wanted to keep it - ultimately I added a second bung to my exhaust so I could run the EFI O2 sensor and the aftermarket dash AFR O2 sensor. I added a fuel pressure sender to my fuel system and a Stewart Warner gauge to my cluster.
You can mount their mini handheld screen to your dash, and see all the sensors, but that didn’t fit the look of my truck.



Fuel delivery
Plumbing and hoses - General
Many options exist for fuel line and fuel hose ‘systems’ - it took me forever to understand that there were various proprietary and non-proprietary products that overlap, with various trade names from various companies. It was hard to tell where to start. Earl's is a good example
Many of the products are flexible hose systems with different materials and jackets and ways to make terminations. I ended up choosing basic hardline and basic hose with barbs.
I used hose in a couple places to handle the vibration from frame to engine, but otherwise ran hardline. For hose lines, I used simple barbed fittings and EFI rated hose clamps - this was simple, cheap and non-proprietary. Many fuel delivery products have a barb option, or it is easy to add a barb fitting on hardline. For hose material, I used Gates Barricade 27349. It’s important to use high pressure and chemical rated hose for this application.



For hardline, I chose nickel copper (nicopp) ⅜ line for ease of forming. I think it was a good choice that allowed me to do some hand tweaking on the truck. However, the ⅜ nicopp is not easily formed by hand - it’s pretty rigid. I almost kinked my longest and trickiest tube when working to hand adjust it on the truck. Luckily I caught myself just in time and didn’t ruin it. The 5/16 and ¼ stuff is much more hand-formable. I used the 4lifetimeline brand on Amazon. Since then, I’ve seen disparaging comments with suggestions to use thestopshop tubing for better formability. The Amazon stuff was hard to bend perfectly - without getting small ripples and flats, so I would try thestopshop stuff next time.
There is a long list of possible hardline fitting types to use. I chose 37 degree AN-6 connections. 37 degree AN connections opened up a wide variety of fittings, adapters, and direct-fit parts. Speedway, Summit, Jegs, are overflowing with items, and the basic fittings were available at a local industrial hardware store. The single flare is easy to do and the various required parts are relatively inexpensive.
Flaring: I used Ridgid 377 flaring tool. I was warned against anything cheaper.
Line bending: I used Ridgid Model 606 Instrument bender. I researched many online - it’s a wide array of comments and reviews. I tried a cheap one that got good reviews on Summit OTC-6515. I returned it - It could not bend the ⅜ nicopp without flattening out the radius. Even the Ridgid 606 with rollers was not perfect, but it was acceptable.
Tube straightener: I used K-tool KTI-72346. And learned that a good straightener is as important as a good bender.
I planned all tube bends on the truck using a spool of 3/32” diameter aluminum wire from Home depot. I used the straightener on the aluminum wire, and then easily hand formed it on the truck to create a pattern.





Fuel Tank planning and mods, Return Line and Vent.
EFI requires a primary delivery line, a return line and a good vent.
A standard vented gas cap does not flow enough in both directions to allow the recirculating fuel system to work properly. Because the fuel tank is in the cab, planning a vent is more complicated than just sticking a vent on top of the tank - obviously the vent needs to be outside the cab. One solution would be to get an external fuel tank, which could make routing the new lines easier, and possibly allow for an in-tank, high pressure fuel pump - simplifying the fuel pump plan. I considered that, but my shortbed doesn't have a lot of room for a tank in the back, and I didn’t want to navigate the filler location problem, and the tanks that might fit were not significantly larger capacity than the 19 gallon in-cab tanks. Stock tank on a slick is 16 gal I think, but the aftermarket replacements are 19 gal. So I decided to modify an aftermarket cab tank and route the plumbing similar to the factory plumbing. I got some ideas from @53deere build thread. Buying a new tank and having it in the garage to plan and pre-build was essential to keeping my truck on the road during this time. I got mine from auto metal direct
Mods to the tank require adding two additional bung locations - one for return and one for vent. I also added a third for a new delivery straw. I got the bungs from bungking.com stepped bungs
I spent a bunch of time planning and prototyping the bung positions, then prepped the tank with holes for the bungs, sanded off the paint, and took it to a good TIG welder. He did some magic on his side to be sure the internal surfaces remained clean, smooth, and free of pin holes.





















I got the straws from Boyd Welding (fueltankparts.com fuel pick up). It’s a bit tricky to locate the straws so they do not hit internal features of the tank. Of course you want the pick-up to be right near the bottom, while the return has more tolerance. Because the bung was at a slight angle from horizontal, my return straw was running into the tank wall towards the bottom, so I cut it short and added a gasoline-submerged-rated plastic tube to extend the length, while also being flexible so I could turn and tighten it into place. BTW, the Boyd Straw is done in stainless, and while I was dry fitting it, it started galling in the bung - I almost damaged something to get it out. I added nickel anti-sieze when I reinstalled it.
I did not re-use the 5/16 factory components because I wanted ⅜ delivery and I wanted my fittings and hardline to match on all three lines. I could have, and maybe should have, used the 5/16 factory line for the return.
The return line should include a straw that carries returned fuel down to the bottom of the tank, otherwise you’ll hear a constant waterfall in your truck. One option sold is a plumbing splice that goes between the filler cap and the tank - you might be able to squeeze it in that area - however you will hear the gas returning.



The Vent is a bit tricky. Because the vent is open to atmosphere, you need to be sure to not create a siphon or easy spillway. I vented mine down out the bottom of the cab so I needed to add some height to the vent line so gas didn’t slosh up and over and out. My first attempted loop was too short, and it spilled out on a full tank sloshing around corners. I replaced it with a taller loop - and that worked. I could not get the ⅜ line to bend up high enough into the corner of the cab, so I spliced in ¼ nicopp, which I was able to hand tweak and coax up into that corner and create a tall enough loop. No spilling now. Consider adding a roll-over check valve in the system. I did not - If I roll completely over, or on the passenger side, my vent will be above the tank. If I roll on the drivers side, I assume the filler cap got torn off and a vent leak will not matter - But you might think differently. I added a porous plug to the end of the vent so no dirt or spiders clog it.







Fuel pump and return circuit
The EFI requires high, continuous fuel pressure at the throttle body. I chose to use a factory gas tank and standard mechanical fuel pump to feed a high pressure electric fuel pump. The high pressure electric I chose is fitted inside a small ‘surge tank’. (Hyperfuel 40009) So it works like an in-tank unit - it is always submerged - which keeps it quiet and cool. I’ve seen a number of reviews of EFI installations that complain about unacceptable fuel pump noise, and my guess is that most simple inline electric fuel pumps would be annoying if mounted near the cab. Mine is on the transmission cross member beneath the passenger seat and I can hear it kick-in and pump when the key is turned to ignition and the EFI primes the throttle body. After I start the engine, the 460 easily drowns it out. However I can see that in a fairly quiet vehicle, this is an important consideration.
The 40009 has an integrated return line - so whatever residual fuel is pumped, returns to the tank. The EFI has the capability to return residual fuel through the EFI unit itself, rather than finding a surge tank that does it. However, this requires plumbing the return line all the way from the EFI throttle body back to the tank - so you need to plumb both feed and return up to the top of the engine. The 40009 return line allowed me to run only one fuel line up to the Sniper - like a carb set up.





Vacuum
The throttle body has a large 3/8 NPT port at the back for a vacuum connection. I used this for PCV. I have a port directly on the intake manifold that I use for brake booster
It has two small ports at the back - one for manifold vac and another for ported vac. Either can be used for distributor vac advance. I capped both of these.
It has a large, plugged, 3/8 manifold port at the front. I unplugged this, added a barb fitting, and used it for my distributor advance. I like the shorter run to the dist at the front of my engine.




Electrical
Holley makes a big deal about direct battery power to their unit. I was able to do this in a clean manner since my battery has separate side terminals.



Integrating switched power to the EFI and to the fuel pump via a relay will depend on whatever electrical system you start with. I was able to make really good use of the extra, unused circuits on my American Autowire kit and a basic ‘relay kit’ from AAW to create a very clean and robust installation. For instance, the AAW harness comes with a 30 amp ‘Fuel Pump’ circuit and 14 ga wire ready to go.
I totally ditched Holley’s convoluted relay harness and the other harness, studied the ‘schematic’ closely, and built the cleanest installation possible with the fewest wires going into and around the engine compartment. Because my basic installation used very few total conductors, I built completely new cables to remove all the unneeded parts and conductors, rather than modifying their cables.
The connectors Holley uses are:
The 7 pin is a Delphi metri-pack 150 series automotive connector 12059472-B
12059472-B
The 10 pin is a Delphi metri-pack series automotive connector 12065425
12065425
With these two connectors, you need to order the correct pins for your wire gauge size, the correct seals for your wire gauge/insulation size, the hole plugs for unused connector positions and the secondary lock for strain relief.
Even though I built smaller cables, the connectors are large and the bundle of connectors is a bulky eyesore to be hidden down toward the bell housing. Also, there is no specific provision for attaching this bundle to anything. I don’t want the wires to break over time due to the large connectors banging around from engine vibration, so I zip tied the connectors to the fuel hardline coming up from the transmission area. On the next go-around, I would choose smaller connectors that matched the required conductor count, and rebuild both the Sniper side and the harness side to make a nice small package.










AFR sender and cable.
Follow the directions on mounting location for the O2 sensor: Near to the manifold and in a spot where condensation won’t foul it. The connector is pretty beefy and the cable from the EFI is somewhat short - I mounted mine on the firewall as shown, but I would have preferred that the EFI cable was longer and the connector was more hidden down on the frame.
I had a local exhaust shop cut and weld-in the bung. I’m wary of the strap-on mounting device they include in the kit - looks like an exhaust leak waiting to happen.







Final set-up and tuning
Follow the Holley basic instructions. It’s straight forward.
On my installation, I had an unacceptable problem with idle control. Searching online I found that this was a too-common problem. There are a handful of ‘standard’ maneuvers and tweaks to try and get the IAC / curb idle working the way intended. I was on plenty of calls with various Holley Tech Support people. After the few regular things were exhausted, I was searching for a vacuum leak, and spent many hours and dollars doing so. Ultimately, I found the problem was that they delivered a Sniper unit with the throttle plates poorly aligned in the bores. The mystery vacuum leak was these relatively large gaps, and I feel they 1) should have sent a properly built throttle body, and 2) tech support should have been able to help me determine this problem before I bought a smoker, pulled my intake manifold, etc, etc.




I aligned all the plates best I could and it got better. I ultimately bought a new set of plates and replaced the plates on the secondaries. After removal, I found my original secondary plates were not flat by about .007” The new plates were not flat by about .004” I bent them a little to get them flatter. Installed and aligned, I was able to get the IAC and curb idle screw to behave as intended. I Also needed to add an external spring to more positively close the secondaries. I tried to add a wrap to the stock spring, but that put it in an overly tweaked spot. This final process for me was a costly bitch that I’m not too happy about. The replacement plates that Holley tech service sent out shipped 3 weeks after I bought my own from Summit and fixed the problem. Not cool - I have a truck to drive.




I also added a short extension to the throttle lever. My foot pedal was too sensitive and very little input made the truck jump and it was hard to control - particularly off idle. Extending by about 7/16ths made a huge difference. I had to increase spring tension on the throttle return to get good balance. Holley sells an extension arm, but I didn’t like the way it extended down to the spring mount hole, so I made my own that used the two holes at the top of the arm.

I like the tunability, here are some examples:
The engine runs poorly until it gets to about 160 F. I set the graph of AFR to temp and RPM to temp to fine-tune the ‘choke’.
It needs a good shot of fuel to start well, so I adjusted the ‘fuel prime’ volume so it starts good and quick every time from outside the truck.

 

Great write up! Hopefully it starts to pay off and run better.

 

Incredible write-up. Great contribution. I thought about the Sniper for the 390 build that I have not started yet. Ended up getting a rebuilt Autolite 4100. I don't have your skill or patience! Your description will help lots of people.

 

Thanks gents. My truck is running well and is stable. Starts up and goes in all temps so far, and zero to WOT without a hitch. Just looked at the thread here on FTE, and it's a lot longer than it looked when I typed it in docs, but I'm confident it will help some guys that are considering the Sniper.
Here's a pic I could have added: Covered the plumbing mess and tank with a simple piece of carpet that matches the carpet kit that I installed. Adds a lot to the look and comfort of the truck, including knocking down cab noise, for little effort.

 

Awesome, man! Very well explained. Holley should have a link to your write-up.

 

Glad to hear that you got that system straightened out and that it works as intended for you. Personally I'm going to stick with my FrankenHolley 650, but I have had a few customers come in with the sniper and issues with it. I will for sure refer back to your write-up in the future.

 

I certainly wouldn't fault you for sticking with the carb.
Are your customer's snipers failing after time? if so, I'm curious what to look out for. Or are they not getting the installation done well?

 

The few that I have worked on were new installations that they couldn't get to run right. I guess I fixed them well, I haven't seen any of them back yet.