This past weekend I replaced the Holley carburetor on my ‘75 Coupe with Holley’s Sniper throttle body electronic fuel injection (TBEFI). The carburetor that came with my Vette was supposed to have just been rebuilt, and it did look very clean, but I was never able to get a big hesitation out of it. I replaced the accelerator pump cams, and put a much larger diaphragm in the accelerator pump to no avail. So I thought TBEFI was the way to go – and it was a good excuse to go a bit modern.

The TBEFI unit

I bought the full Sniper kit which included the external fuel pump, hoses, etc. I also bought the distributor, coil, and spark controller. This would allow the TBEFI to also control the timing. The recommendation was to first get everything running correctly with just the TBEFI, then add the timing functionality – and I always follow recommendations. . .

I had watched videos of mechanics installing TBEFI and they made it sound, not easy, but very doable in a few hours time. Why is it always different for me?

Mounting the fuel pump

The first task was to install the fuel pump. About the only place I found was beside where the catalytic converter shield was. I found that the supply line had a splice near there, so I wouldn't have to cut the line. The tank was almost empty, so I blew into the line at the carburetor to push the fuel back into the tank, and pulled this splice off. Above it was the return line (the supply line was 3/8 but the return line was ¼ inch. Holley recommends 3/8 line for both – I hoped to get away with the ¼ inch return). I could see that the return line was badly rusted at this point, and realized that this was the reason for the splice on the supply line. I thought about cutting the return line to replace the bad section, but there was no room to get even a saw blade in anywhere. I did cut the supply line forward a bit so the flexible line would not have to make a sharp “U” turn and kink.

After buying compression fittings for the fuel line to hose, I mounted the fuel pump and per-filter. All this sounds easy, but it took me over 3 hours of aggravation working under the car without a lift.

Installing the TBEFI

Next I removed the carburetor and installed the TBEFI unit. I couldn’t believe how many wires there were! Many of these were for cooling fans, air conditioner, and electronic distributor that would not be used at this time. The instructions were very clear and I was able to hook everything up correctly. This included mounting a temperature sending unit and drilling the exhaust for the oxygen sensor.

Starting the car.

I started the car and it fired right off but the idle was very uneven and something was making a loud scraping noise. I checked the fuel pressure, which is supposed to be 58.5 psi, but it was running at 80 psi. Probably the reason for the bad idle, but what about the scraping noise? Discouraged I left it for dinner and some TV. Finally I went back to the garage and ran the return line to a gas can, and started the car. It ran fine and no scraping noise!

Remember that ¼ inch return line that I tried to get away with using? I didn’t get away with it. In order to replace it, the gas tank needs to be dropped, which requires moving the mufflers and spare tire carrier. I don’t do mufflers, so I’ll take it to my mechanic and have him run a new return line. In order to get to the mechanic’s shop, I’ll run a return line across the top of the Vette and into the gas filler!

Altogether I have 16 hours into this project. I’d say it was well worth it. The car is extremely responsive now, no hesitation when I jump on the gas and it almost fly's!

Once my mechanic has the return line routed under the car, I’ll add the new distributor and spark-control box.

Congrats Bill!! Thanks for sharing that story with us....I'm sure there are others contemplating going the same route on their cars. 😀

Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Wow, and I thought putting a 65 Rochester FI unit on mine was a lot of work. At least I didn't have to fool with the gas lines.

Congrats on sticking it out. Be sure to let us know when you get the rest of it completed.

1973 L-82 4 spd

Great write up Bill.  Keep'em coming!

Ah, the trials and tribulations of installing an EFI-TB system.  When putting the system on "BLKBRRD" I spent more time doing routing of fuel lines and electrical stuff than the actual unbolting the Q-Jet and bolting on the TB unit.  If I've learned anything during the process I should have gone with an in-tank fuel pump.  I had been advised against using an in-line pump and didn't want to tackle the installation of an in-tank pump so opted for an external fuel canister that houses an electric pump.  The 1st and 2nd designs of that unit were flawed which caused fuel delivery problems (I've heard that a 3rd version of the unit is now on the market).  I found a fix on-line to the unit that I have made (which also included more fuel line plumbing) and so far the whole system is working a little better (still working on my confidence in the system though).

Bottom line - I'm wishing that instead of buying the EFI-TB system I would have put that money towards having the Q-Jet rebuilt by a seasoned carb guy and then had the car professionally dialed in.  Thinking I might have spent less money to-date and have more confidence in the car.

Bill - if you have to drop the tank anyway consider putting in an in-tank pump.  Good luck...!!!

Jim Olson 

"The Toys"...!!!  Save the Wave!

Where I've been in a Corvette...!!!

I thought about an in-tank pump, but It looked a bit complicated to mount one in the tank (with other style tanks you can cut a separate opening for the pump, and that looked fairly easy, and there are EFI tanks available for the earlier C-3's), and I was hoping to be able not to drop the tank.  I'm taking the car to my mechanic this morning, so it's a bit late for getting an in-tank pump (hope I'm not making a mistake. . .)  I do hear the wine from the external pump, but it is not too loud.  Yes, I think if I did it over, I would find a way to use an in-tank pump.

I only drove the car a mile or so so far, but I was very impressed.  I don't think a carb could replicate that.

Great job

please put up some pictures once you get it all done 

Brian - NCM Lifetime Member

73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System