1986 2.5L to 3.4L: Amateur Hour

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I've posted about this truck in other threads, but my last update was about 18 months ago. Another user had then suggested I start a project thread to document the build.

Background
We bought an electric commuter car in April 2022, so I figured I didn’t need my newer Subaru for house projects or hauling the paddleboard on weekends. In August 2022, I bought a 1986 Jeep Comanche with a 2.5L engine and a 4-speed manual transmission. The previous owner made a few modifications, like an electric fan with some questionable wiring, replaced parts of the interior with components from a Chevy Silverado, and an odd sliding motorcycle rack bolted to the bed. I had never done any work on a vehicle before, aside from topping off wiper fluid. I paid a mechanic to work on the differential and fix the missing passenger seatbelt bolt. I wasn’t planning on turning this truck into a showpiece or a rock-crawling off-roader, but I did notice 2.5L engine struggled to keep up on the highway, maxing out at about 65 mph during my commute.



Not long after I bought the truck, I started noticing the idle getting rough. About two months after buying, the engine quit working altogether. A neighbor found that the fuel coming out of the injector was not flammable. Given that the rainy season had just started, I figured rainwater invaded the fuel tank, either from rust or wild drilling when the previous owner install the motorcycle rack. My neighbor said I should consider replacing the injector with a carburetor, but he also mentioned that he had a 3.4L engine from a 1994 Camaro sitting in his garage. I knew from this website that some owners swap 2.8L engines for the 3.4L from a 1993-1995 Camaro. He said I could have the engine for free.

That was two long years ago.

I understand that this build would be more difficult because I couldn't just pull compatible parts as is the case with a 2.8L. I cleaned the 3.4L, removed the 2.5L and accessories (without knowing what most of it was exactly), had a welder modify the oil pan to make sure it would clear the differential, replaced the clutch, machined the flywheel, I even had the welder fabricate custom engine mounts (I got tired of searching for them after a salvage yard crushed a car I spent a precious Saturday pulling the rusted accessories off). I bought a new upper intake manifold, exhaust manifolds, an ECU from ebay (hopefully coded properly with the VIN I gave them), had a salvage yard pull an engine harness from an automatic 3.4L Firebird, new accessories, accessory brackets from ebay.




 

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By December 2023, I had the 3.4L installed and was bolting in the exhaust manifolds.
 

I broke a bolt in the cylinder head and I took the head off to have it professionally drilled out. I was horrified to find the cylinders were full of rust beyond what could be ignored of fixed with steel wool.
 

 

The machine shop also tested the head: warped. I bought remanufactured heads from OReilly's for roughly $400 and paid $2k for the machinist to bore the cylinders, deck the mating surface, supply new pistons and bearings, and polish the crankshaft. I got the engine back around early spring and rebuilt the engine. At this point feel like I've replaced nearly everything on it. Countless trips to Ace to find the right bolts. The total cost has far exceeded what I would have spent on a crate engine, but then I wouldn't have learned how to install Helicoils in a newly machined engine block near the cylinder head mating surface.


(Unsure what happened with area after spending all that money machining the mating surface)

Now I'm on to wiring, which everyone has told me will be the most difficult part. I've pulled the old ECU (near driver's right knee if anyone is doing this) and attached harness. I've figured out all but one or two connectors on the new harness. My understanding is I need to delete

1. the A/C (I deleted and replaced with a dummy pulley)
2. transmission (this is a manual)
3. level sensors and coolant temp sender (will be wired to the dash)
4. C100 &C210-230 connections to non-engine Camaro harnesses.

(I cracked the aluminum valve covers I so carefully painted red; they may not have been 100% compatible or I just over torqued)
 

I will also need to figure out a new relay/fuse system. And figure out the antitheft bypass. And install the fuel pump, line, and power. And finish the coolant system. And power steering. And vacuum tubes. And drop the tank to figure out how this all started.

I've found CC users to be genuinely helpful in my other posts and in the guides I've reviewed. I document my struggles and progress should this be of any use to someone or if anyone has suggestions moving forward. Cheers.