FigurativeGarbage Posted October 22 Share Posted October 22 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. Link to comment Share on other sites More sharing options...
FigurativeGarbage Posted October 22 Author Share Posted October 22 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 the A/C (I deleted and replaced with a dummy pulley) transmission (this is a manual) level sensors and coolant temp sender (will be wired to the dash) 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. Link to comment Share on other sites More sharing options...
The86manche Posted October 22 Share Posted October 22 If you cracked the valve cover you may have over torqued or they were the wrong bolts. That is quite unfortunate hopefully you still can use it Link to comment Share on other sites More sharing options...
FigurativeGarbage Posted October 22 Author Share Posted October 22 1 hour ago, The86manche said: If you cracked the valve cover you may have over torqued or they were the wrong bolts. That is quite unfortunate hopefully you still can use it It's okay, they were aftermarket aluminum valve covers. I kept the original covers just in case. Glad I did. Link to comment Share on other sites More sharing options...
The86manche Posted October 23 Share Posted October 23 6 hours ago, FigurativeGarbage said: It's okay, they were aftermarket aluminum valve covers. I kept the original covers just in case. Glad I did. Those are aftermarket? They look like fiero valve covers to me. I have a set of real fiero valve covers I'd sell if you'd like. They do require specific bolts and unfortunately I lost them though. They have a collard washer on them. Link to comment Share on other sites More sharing options...
FigurativeGarbage Posted October 23 Author Share Posted October 23 I got them from my neighbor. I'm sure you're right. Appreciated, but its okay. The original ones are on now. Mostly an aethetic thing anyways. Link to comment Share on other sites More sharing options...
M.T.Hands Posted October 23 Share Posted October 23 Good write-up, and you have come a long way in your transformation of "filling the windshield washer fluid" to a mechanic, I have always seen that, experience is the best teacher (and I'm living proof), good work Link to comment Share on other sites More sharing options...
Drahcir495 Posted October 25 Share Posted October 25 Sounds like you did a lot of work to it yourself - . Do you have it running? I don't remember ready that. Link to comment Share on other sites More sharing options...
FigurativeGarbage Posted October 27 Author Share Posted October 27 I'm currently working on a standalone ECU harness. I’ve de-pinned around 17 wires from the ECU connectors. Most of these were related to automatic trans and AC functions, which are unnecessary for my standalone setup. (not my photo, but used for initial reference) (one of the Camaro manual diagrams) I've been looking at connectors C100, C210, C220, and C230 that connect to lights and the body harness. Example: the C220 alternator connector powers the dash. I have a GM VATS bypass from Timers. I need to figure out speedometer and fuel relay wiring. (The C220 only has two wires in it right now, and matching connector. I'll need to figure out the clutch anticipator.) I also discovered a mystery component with brown and black/white wires that seems to be tied to the oil level sensor area (it has some kind of recessed button that clicks when pressed). The actual oil level sensor connector nearby has two-black-wires. I'll trace the wires back for both if I have to. (Manual reset button? Diagnostics? Kill switch? Jetpack handheld ignition control?) Link to comment Share on other sites More sharing options...
FigurativeGarbage Posted October 28 Author Share Posted October 28 Cleaned up my hand-drawn diagram on Lucidity. I believe I found one solution to this set up: a VSS dual bypass (Dakota Digital SEN-01-4280). This allows the mechanical signal to go to the dash and converts an electronic signal to the ECU. I believe the B28 Buffered Speed Output sends to the dash and therefore can be removed. I'll next make a list of the C100-230 wires that need to be resolved (fuel pump relay, etc) Link to comment Share on other sites More sharing options...
FigurativeGarbage Posted November 3 Author Share Posted November 3 I removed the starter solenoid because the new starter has an attached solenoid. I'm thinking I'll keep the ignition relay. I removed the ICU/distributor (between the original fuses and alternator). The standalone wiring harness is largely thinned save for figuring out the C### connections. I need to clean up the remaining original wiring a bit more (A/C related, I/P to engine connectors, etc.). It is harder to find information on the 2.5L Comanche; the service manuals are not as thorough as the Camaro manuals I've been using for the engine (wiring diagrams for the instruments, headlights, etc.). Link to comment Share on other sites More sharing options...
eaglescout526 Posted November 3 Share Posted November 3 1 hour ago, FigurativeGarbage said: It is harder to find information on the 2.5L Comanche; the service manuals are not as thorough Not entirely true. I’ve got a few manuals that cover the engine and fuel system. Link to comment Share on other sites More sharing options...
FigurativeGarbage Posted November 4 Author Share Posted November 4 It has those sections, for sure, but they don't have the illustrative diagrams that I found helpful as an amateur (pinouts, harness routes, etc.). If I'm wrong, let me know what page or upload (if you have have a chance). For example, white, yellow, and green run to the axle and I am guessing they are the 4wd actuator. Identifying these will take some time, but I suspect they are no longer necessary unless they run to the gauges. Points if you know what this is. Link to comment Share on other sites More sharing options...
eaglescout526 Posted November 4 Share Posted November 4 30 minutes ago, FigurativeGarbage said: Identifying these will take some time, but I suspect they are no longer necessary unless they run to the gauges. That still the 2.5L harness? If so, there is some stuff in there that runs to the gauges. And I have an 86 wiring manual that I can use to help you identify which one is which. 30 minutes ago, FigurativeGarbage said: Points if you know what this is. 4wd light switch for the cluster Link to comment Share on other sites More sharing options...
FigurativeGarbage Posted November 12 Author Share Posted November 12 Spent some time this weekend sorting the original engine bay wiring a bit more. There are still several mystery connections to resolve (hanging outside of the cabin in the pic below). I removed the auxillery lights and relay for now. I also removed the fuel pump and what I think was the B+ latch relays as they look pretty corroded. I ordered a relay box and bus bar to help clean things up. I'll also relocate the electric fan relay the previous owner installed. Frustratingly, I found water in the passenger side cabin. I see in other posts this isn't terribly uncommon and is likely either the hood hinge seal or the blower/heater seal. I'm not wild about pulling the dash right now. Goal is to try and get the motor started soon. Link to comment Share on other sites More sharing options...
Ωhm Posted November 12 Share Posted November 12 RED wire with single connector, if HOT AT ALL TIMES, is used for Engine Compartment Lamp, when equipped. Two YEL wires could be Resistor Pack for Automatic Transmission. Relay Block with Two PNK wires is/was B+Latch Relay. Link to comment Share on other sites More sharing options...
FigurativeGarbage Posted November 17 Author Share Posted November 17 Dropped the tank and pulled the sending unit. As I suspected, there's a hole near the rear grommet that is likely the source of water contamination. After I get a new tank, I need a fuel sending unit that will deliver 36-50 PSI to the Camaro engine. I prefer to do it in tank, but I'm not interested in figuring out a complicated custom system. I may do in-line so I can get this fired up this year. I'll need new fuel lines for the pressure in any case. Open to thoughts. Link to comment Share on other sites More sharing options...
FigurativeGarbage Posted November 17 Author Share Posted November 17 Looks like I'll go for the MTS JPSU-6P4.0. Seems like it will provide enough flow and PSI for the 3.4L. https://www.mtscompany.com/sendingunits.htm $39? Its like $65-$160 everywhere else: https://a.co/d/hePOZeq Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now