Gillette, WY24 posts · joined Nov 20251985 Chevrolet K10, 350, TH400
i keep bringing this up in other threads so here is the whole writeup in one place. i put a self-learning throttle-body EFI unit on the 350 in my 85 K10 last spring, the kind that looks like a four barrel and bolts to a standard intake, and i did it instead of an LS swap because i wanted to keep my own engine. we sit at about 4,500 feet here in Gillette and my Quadrajet needed a different setup for January than for July, and i was tired of it.
what it actually took, because this is the part the box does not show you. the throttle body itself is the easy hour. the work is the fuel system. a carb runs on 5 or 6 psi, EFI wants around 58 psi and it wants a return line back to the tank, so you are running a high-pressure pump, new feed and return line the length of the truck, and a regulator. i added an in-tank style high-pressure pump and ran 3/8 hard line front to back. that was the weekend, not the throttle body.
you also weld an oxygen sensor bung into the exhaust ahead of any leak so the thing can read what it is doing and tune itself. and you decide whether to let it control timing off a signal or lock the distributor out and leave timing alone, which is its own rabbit hole.
my question for the board, since a few of you are circling this: for a plain driver, is the cold-start and altitude payoff worth the fuel-system labor, or am i a guy who spent a weekend and 1,200 dollars to fix a problem a carb rebuild and the right jets would have mostly solved.
drum_to_disc_swapWeekend wrench#2
Kingsport, TN29 posts · joined Nov 20251976 Chevrolet C10, 350, TH350
the altitude part is where this earns its keep and people at sea level do not get it. a carb meters fuel by the air it can pull, and the correct jetting at 4,500 feet is not the correct jetting when you drop to Denver or climb a pass, so you are always a little rich or a little lean somewhere. EFI with an oxygen sensor just trims for it on the fly. for a truck that lives at one altitude a good carb is fine, for a truck that changes elevation a lot the EFI is genuinely better, not just newer.
down here where i am near sea level and it never gets truly cold, my Quadrajet rebuilt with the right kit starts fine and i would not spend the 1,200. so the honest answer to your own question is it depends entirely on where the truck lives, and Gillette is exactly the place it makes sense.
squarebody_frame_offRestorer#3
Amarillo, TX44 posts · joined Nov 20251984 Chevrolet C10, 350, 700R4, frame-off
happy thanksgiving, i am hiding from relatives in the shop. one caution on the self-learning units that i learned the expensive way on my build. the return line is not optional and it is not the place to cut a corner. i tried to get away with a returnless regulator setup at the throttle body on the first go and it heat-soaked sitting in Texas traffic and gave me a hot-restart stumble that drove me up a wall for a month. ran a proper return to the tank and it vanished.
also weld the O2 bung in, do not use the clamp-on exhaust bung the kit includes as a shortcut. the clamp ones leak, the sensor reads a lean signal that is not real, and the unit chases its tail trying to richen a mixture that is actually fine. ask me how many evenings i spent on that.
carb_to_efi did it the right way the first time by the sound of it. return line, in-tank pump, welded bung. that is the version that works.
obs_ford_f150Daily driver#4
Tulsa, OK21 posts · joined Nov 20251990 Ford F-150 XLT Lariat, 5.8 351W, E4OD
the ford version of this thread is almost funny, because my 90 F-150 already left the factory with EFI on the 351W in 1990, so the ford crowd went the other way and some guys carb-swap the early fuel injected trucks when the old speed-density computer acts up. grass is always greener.
but reading yours makes me want to leave my factory EFI alone and just maintain it, because you are describing a lot of work to get to where my truck started. for you chevy guys with a carb, if the truck lives somewhere cold and high, the throttle-body kit sounds like the move. the return line labor is real either way.
carb_to_efiOPWeekend wrench#5
Gillette, WY24 posts · joined Nov 20251985 Chevrolet K10, 350, TH400
reporting back now that it has seen a real cold snap. we hit nine below one morning last week and the K10 fired on the second crank, no pumping the pedal, no fast idle to babysit, no praying. that is the whole reason i did it and it delivered exactly that. it idles down on its own as it warms and i do not touch anything. a year ago at nine below i would have been out there with a hair dryer on the Quadrajet and a prayer.
on the is-it-worth-it question, my honest answer after a full winter: for me, yes, because of where i live, and no if i lived where drum_to_disc_swap does. the unit tuned itself in about 30 miles of driving and the handheld lets me watch what it is doing. i ran the Holley setup and their homepage has the install docs and the base maps if anybody wants to read the real instructions before they buy, it is at holley.com. i am not selling anything, i just read those three times before i cut a fuel line and it saved me.
the one thing i would tell my past self: budget two weekends, not one, and do the fuel system first and carefully. the throttle body is the reward at the end, not the job.
rust_repair_panelsRestorer#6
Dothan, AL38 posts · joined Nov 20251983 GMC C1500, 305, TH350
one rust-guy footnote since you ran new hard line the length of the truck. when you drop the tank or run new line on an old truck, that is the moment to look hard at the top of the fuel tank and the straps, because they rust from the top where road spray sits and you never see it. while you had it apart was the time. if you did not, pull a flashlight up there next oil change before a strap lets go on the highway.
good writeup. the EFI itself i have no dog in, but anybody running fresh fuel line past 40 year old tank straps should know the straps are usually worse than the line they are replacing.
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