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C3 Fuel, Emission Control, and Exhaust Systems

Replacing Carb with Fuel Injection? (1/8)
 5/24/19 3:00pm
BillHanna
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Cana, VA - USA

Vette(s):
1975 Stingray


Joined: 7/3/2016
Posts: 168

I'm thinking of replacing the Holly carb on my '75 Coupe this fall with a Throttle Body Fuel Injection system.  I'm looking for insight as to issues in doing this.

(I have never been able to get the Holly working just right -- it is very cold natured, and even when hot hesitates when jumped on quickly.)

 

I understand that the return line from the existing fuel pump goes to the charcoal canister.  Can this be used as is for the return line on a TBFI system?

 

Anything else I should be aware of before I jump into this change?  Preferences as to which brand to use?



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Re: Replacing Carb with Fuel Injection? (2/8)
 5/24/19 4:08pm
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 565

If I'm not mistaken I believe the lines to the charcoal canister go to the vent on the gas tank and the other one goes to an intake manifold port. The return line on the fuel pump on my 73 goes back to the tank. Maybe they changed that when they went to catalytic converters but I can't imagine pumping gas into the charcoal canister.



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1973 L-82 4 spd

Re: Replacing Carb with Fuel Injection? (3/8)
 5/25/19 1:42am
NorskyLifetime Member
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Twin Lakes, CO - USA

Vette(s):
SOLD - "The Toy" - 1970 Convertible
SOLD - "The Beast" - 1990 ZR-1 (#682)
"BLKBRRD" - 1978 Trans Am, 400ci/225hp, 4 spd, Black w/black interior, Hurst t-tops


Joined: 1/23/2002
Posts: 6842

I'm in the process of transitioning "BLKBRRD" from its original Q-Jet carb to a TB EFI system.  I'm using a self-contained external fuel pump that was originally sold by the brand but is now not available from them as they are now recommending either an in-tank pump or an in-line pump.  The charcoal canister that I pulled off the car as part of the conversion had four lines - 3 attached to the Q-Jet and one vent line to the fuel tank.  Two of the lines attached to the Q-Jet were return/vent lines to the canister and one was a vacuum pull from the canister to the Q-Jet.  From what I've read fuel vapors were brought to the canister via the return/vent lines from the Q-Jet and the vent line from the fuel tank and then pulled from the canister into the Q-Jet via the vacuum pull line for combustion - all part of the emissions systems.

Because I'm using the self-contained external fuel pump no return line to the fuel tank is required - but the vent line from the fuel tank does connect to the pump unit.  Using either an in-tank or in-line fuel pump requires a return line to the tank.

The physical unbolting carb-related parts and bolting TB-related parts was rather straight forward as was most of the electrical connections.  I struggled a little with finding a "keyed" power source but was eventually able to clear that hurdle with the help of forum members.  The biggest issue I'm facing now is getting the EFI's "brain" dialed in.  All the EFI jargon is "greek" to me so I'm stumbling through trying to understand which parameters do what, how they interact/interplay with other parameters and how to get them all to "play nice together".  I did find a forum that addresses topics and issues related to the brand's products and I'm spending a lot of time there reading and learning.  Hopefully I'll be able to get everything dialed in before heading north in July.  If I can't I'll either rebuild the Q-Jet and reinstall it or drive a different vehicle.



|UPDATED|5/24/2019 10:42:14 PM (AZT)|/UPDATED|


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Re: Replacing Carb with Fuel Injection? (4/8)
 5/25/19 6:00pm
ateupjoeLifetime Member
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Cleburne, TX - USA

Vette(s):
1978 Stingray - needs a little TLC, bought for wife's 50th Birthday


Joined: 4/10/2010
Posts: 15

Can’t wait to hear more about this project as I’ve thought about doing the same.



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1978 50th BD gift to my bride

Re: Replacing Carb with Fuel Injection? (5/8)
 5/25/19 11:00pm
johnu
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Scottsdale, AZ - USA

Vette(s):
1981 Corvette Two-Tone Claret color, 4 spd, C7 Vert


Joined: 5/23/2007
Posts: 564

Darryl (Sarge) just got done hooking up a Holly system.  He did a FITech last year.  I'll
ping him to visit here.

https://www.facebook.com/100010265464566/videos/852356275116547/?id=100010265464566



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      Only 27 years together
Re: Replacing Carb with Fuel Injection? (6/8)
 5/27/19 12:58am
Sarge81Lifetime Member
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WEST SENECA, NY - USA

Vette(s):
1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.


Joined: 12/3/2001
Posts: 2379

Hi John, you rang? My things have changed here a bit. 

Bill Hanna,

 I did a FiTech EFI unit on my wife's 1987 Olds 442 with a built Olds 350 engine. I had one of their first generation EFI units and had issues with it. The major one was the ECM died after 300 miles. I was not happy they would not warranty it because it was over a year old. I explained to the guy at FiTech that this car sits in a garage all winter and only gets driven in the summer. So $300 later they fixed and updated the ECM. The car runs better that the last unit, but I have to do some tweaking yet. I'm not completely happy.  I might even ditch the FiTech and put a Holley Sniper on instead.

I just wrapped up a Holley Sniper EFI unit on a friend of mine's 1971 Impala Pro Street car. It has a 454/425hp crate engine from '99 in it. It was like night and day difference from setting up the FiTech unit. The Holley was basically bolt it on, wire it, revamp the fuel delivery system and adjusted the idle screw. The car is no longer a cold blooded beast. It's now a beast. 

I highly recommend a Holley Sniper EFI. They make a spread bore model now. So if you have a Q-jet spread bore style manifold on the car I would recommend getting the spread bore Sniper unit. 

When doing your fuel system, you can use most of the steel factory supply line. You have to figure out a spot to mount the primary fuel filter, fuel pump and secondary fuel filter. They supply ample amount of high pressure neoprene fuel line so you can make your connections from the factory steel supply line to the tank and on the other end, from the steel line to the EFI unit. Then use the supplied neoprene line and run that from the EFI unit back to the tank. Leave the vent line hooked up and tuck away those unused lines at the charcoal canister so they will vent overboard. I have yet to have any issues with gasoline fumes from the unhooked emission hoses. 



|UPDATED|5/26/2019 9:58:32 PM (AZT)|/UPDATED|


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Re: Replacing Carb with Fuel Injection? (7/8)
 5/27/19 10:57am
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 19658

I've done trans work on several vehicles with the Sniper EFI set-ups, and each one of the owners were super happy about how freekin easy they were to set up. I can attest that they DO work very well....instant starts, excellent throttle response, and they look kewl too. One vehicle was an '88 Yeep Wangler with the 6 cyl, and it was freaky how well it ran. 



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Joel Adams
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Re: Replacing Carb with Fuel Injection? (8/8)
 5/31/19 11:35pm
BillHanna
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Cana, VA - USA

Vette(s):
1975 Stingray


Joined: 7/3/2016
Posts: 168

Guess I'll put a Sniper EFI on my wish list for this fall.  Thanks all for your insight!

I just checked my mileage since I rebuilt the engine this winter and I'm getting over 21MPG.  I think this is quite good for a carb car.  What do you think?



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