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Ls swap trouble

have a 1986 Chevy c10, me and my dad have been restoring it for almost 4 years, and had the occasional Chevy oil leak, so one night I drove it like a dumbass and blew the engine, we eventually swapped it with a 6.0 vortex out of a 2001 Chevy 1500HD and kept the TH350 turbo trans, we stripped down the wiring harness down to 5 fuses and 2 relays, engine runs sound at idle, has no problem starting up, has a maf, no catalytic converters, o2 sensors that go before the catalytic converters that I don’t have, and new fuel pump supplying 60psi of fuel to the engine, and new spark plugs and wires, my issue is when I want to floor it, the engine drops, sputters and backfires like hell, but when I baby the gas pedal it’ll go smoothly. My issue is it takes a solid 5 min for me to get above 35 mph, and I’ve almost got into multiple wrecks in a truck with no airbags. Anything will help please, my dad and I are stumped.
not to mention that we also deleted the EGR, VAT, Rear O2 ect (nessicary things) off the ecm.

A fuel injected engine requires O2 sensors in order for the computer to provide the proper fuel mixture.


My first thought too. But I wasn’t sure if he was referencing not having the 02 sensors, or the cats, or both?

I think you and your dad had a good time getting that truck running but making it a reliable daily driver might be an unreachable dream. You might have better luck starting over with a carburated 2.8L

I’d be in over my head trying to guess what the issue is. I don’t know if you’ve got enough wiring, sensors, etc to run the engine via the pcm. Assuming this thing’s always run this way since the swap, something got deleted that the computer needs in order to operate the engine.

I’d think the computer would need some input from a speed sensor on the trans, so not sure how the electronically controlled engine is operating with a hydraulically controlled turbo 350 trans. I’m sure there’s a way around that, but again, over my head.

I’d suggest hooking a scanner up to the engine via the obd port (if it’s still there). Might get some clues on what’s going on that way.

If the engine and trans are together and in the truck, the easiest thing to do would be to swap intakes and run a carburetor, assuming he doesn’t figure out the issue(s) with the pcm / sensors / wiring.

You went to 6L engine and have 60psi but are these the original diameter fuel lines? Also, is this original tank with external high pressure pump or did you retrofit fuel tank and internal pump? Describe how fuel supply is configured…

I don’t have any catalytic converters at all, on a normal 2001 truck it would have 4 o2 sensors, 2 before the catalytic converters on the headers and 2 after the catalytic converters,
Since I don’t have any cats I put just 2 on. The ones that would be on the headers

The reason I swapped from a carberator to an ls is 1. I blew up the 350 with the carb. It backfired every morning even after we rebuilt it and swapped it with a Quadra jet.
2. The 6.0 was in easy reach for a good price and it was something that my father and I where planning on doing later on down the road. Noting that I’m still in high school and running a minimum wage job.
3. It’s handling better than it ever was with the carb. I haven’t had any trouble with it other than the fact that I can’t floor it

We tapped into the tank and ran a line to a pump that supplies 60psi of pressure and ran that up to the engine. We are not running old lines considering they’d bust from the pressure. We even ran new return lines for the back flow.

My plans are to keep the vortec that I put in it, it took my dad and I 2 months to do, carburetors are fun to have and helpful to work on, but my dad and I are dead set on this vortec swap, it runs better than it ever has, the only issue would be when I wanna floor it. I’m having no other issues with it

What does the computer tell you? It is surely throwing codes…read them and follow the breadcrumbs. There should really be nothing mysterious here as you are surely using the engine harness and computer that is supposed to run the new engine. Definitely do NOT go to carburetors…that would be a terrible step backward. If you have fly by wire throttle then you should run through the relearn procedure just for fun. If you did the swap correctly this engine shouldn’t even know its in another vehicle. Pull the codes, you definitely have some.

All gasoline engine options on 1986 C-10s were carbureted. I seemed to have “mispoke” myself when I recommended the 2.8 which obviously wasn’t available on that truck but I can only imagine the Rube Goldberg engineering to get the EFI 360 engine installed and operating. And I can’t imagine the OP ever reaching a satisfactory result moving forward from the current situation while installing a pre-feedback carburetor and mechanically controlled distributor on the original engine would have been a likely workable solution to what I’m sure was a failed feedback system.

OK, that’s better than keeping the old lines. However, it’s not just about pressure. That creates the appropriate spray pattern from the injectors. What I’m focusing on is fuel VOLUME. Your engine is falling on it’s face under load. It has a questionable fuel source that’s not the same design used on this 6L engine. You should do a fuel volume test to ensure it has sufficient fuel supply. You can jumper the fuel pump and direct the line from the rail into a jug to measure volume per minute.

Curious, how did you tap into the existing tank? If you just connected your new lines to the old tank’s outlet, there may be insufficient diameter on the lines going in. Any restriction in the line is worth considering but especially on the inlet to the pump. They are good pushers but not so good pulling, plus the diameter may be too much restriction for the flow requirements of the new engine.

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