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1994 Dakota 3.9 to 5.2 swap questions

682 Views 25 Replies 4 Participants Last post by  cwkerr007
I've recently become the new owner of a '94 Dakota. 3.9 V6 M/T 4x4. For a truck that's approaching 30 years old, it's in great shape! However, it has 230k+ miles on the original 3.9 V6, and I'm seeing some leaks and hearing some noises that hint at an engine rebuild in the future.

Or... after doing a bit of research, it looks like the 5.2 V8 is a pretty easy swap! I have several other projects, so this will probably be a gradual "grab parts as they turn up" process, not a sprint to completion. However, I wanted to run through what I (think I) know now, and maybe get some feedback from folks to help plan this out.

1. 5.2 engine. We have a few decent yards nearby and I can get a running engine from a wrecked truck for pretty cheap. Ideally I'd just freshen up the top end. It looks like anything from 92-96 will work? Since the 3.9 and 5.2 are very similar blocks, can I retain all my accessories and accessory brackets from the 3.9?

2. ECM from a 5.2 M/T 4x4 truck (PN 56028263). I've seen a few of these remanufactured for about $300. I'm comfortable re-pinning my harness for the two additional injectors (I've built a few harnesses from scratch). I have a 1994 FSM on the way for wiring diagrams.

3. Exhaust. I'll probably pick up a set of factory manifolds with the engine. I can fabricate the rest of the exhaust myself. Will probably do a y-pipe, cat, muffler, and single exit - as close to factory as possible (also means I can use the same hangers).

4. Front suspension. Here's where my lack of knowledge about torsion bar setups shows. I know on a truck with front springs I'd need heavier springs for the extra weight of the V8. Do I need to swap parts with a torsion bar setup, or just adjust the bars?

5. Electric fan, radiator, and shroud modification (or removal). I think an efan is the way to go (makes for better throttle response). I believe I'll need a radiator from a V8 truck (but please correct me if I'm wrong). Also, I'm pretty sure the V6 radiator shroud won't work without modification, but I can figure that out.


I know some folks might chime in with suggestions for more power (cam, 1.7 rockers, dual exhaust with headers, etc etc) but I'm planning to retain the original transmission (which should be the AX15). I'm not trying to put down huge power numbers or hit the strip/track, so the AX15 will do fine behind the 5.2. I like wrenching, and I figured for a bit of extra time and money I could have a neat project AND a more capable truck.

Thanks in advance for any feedback or info!

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Gotcha, that's good information to have. Mine seems solid right now, shifts very smooth and there's almost no play in the shifter. Hopefully it stays that way, but if not I wouldn't mind swapping to an NV3500 when I do the engine swap.

As an aside, I got my registration and plates today. The first batch of tune up parts has arrived (I'm doing oil/filter, air filter, front pads, wipers, plugs/dist cap/rotor, shocks, and a partial brake fluid flush). I'm also going to be reworking the stereo - it works, but one speaker is blown and the wiring to the other one only has an intermittent connection. I'll be hauling slash to the slash yard this weekend for sure though.

I've also noticed that the AC seems to work! I say "seems to" because the line under the hood gets cold, but I'm not getting cold air out of the vents. All the actuators work (I can toggle floor/blend/dash/defrost vents). I removed the cowl and sucked out some leaves and other debris, but I can't work the hose down into the area behind the dash. I'm thinking something might have built a nest around the evaporator, and air is being drawn in around the evaporator instead of passing through it. Am I on the right track here? Anything I can do to test that theory or clean that area from the outside? I'm looking for any option that would save me pulling the dash apart, I can do the work but MAN do I hate tearing into dashboards. I'd almost rather live without the AC.
You say the tube is getting cold but is it sweating and when the ac is on do the vent blow as hard as the heater ? If you or short on coolant that core will freeze up and stop airflow. Just giving you an option to look at good luck hope u get it 馃槑
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So simple I can't justify putting off the upgrade any longer!

I've sourced a used 5.2 for $550 with ~200k. Complete from TB to oil pan, with the factory exhaust manifolds and injectors. Only thing I won't have are the accessory brackets - but I think those should be the same between the 3.9 and 5.2?

I'm also doing some research on common 5.2 issues and things I'll need to look for and address. The big ones seem to be the intake plenum gasket and camshaft position sensor. I'll plan to replace both of those, but is there anything else folks would recommend doing before I drop the engine in the truck?

I've blown through all my discretionary income for the next couple months, but I do have a source for a 5.2 MT ECU, which should be the last major piece I need (well, unless the clutch is shot). I'll use that time to pull the pan and intake and see if there are any major issue with the engine, and maybe get a start on the wiring (I don't see any reason why I couldn't wire the two new injectors with the 3.9 still in the truck so they're ready to go for the swap).
i have two 94 5.2 auto for parts both run so if you need anything you can have it better to reach me through text so you'll have to pm me but one last thing if you have to do the clutch make sure you have a shop surface the flywheel or you will have a shudder when you release the clutch hope you get her goin like you want !!! sorry for slow response i only get on line at home after work
Thank you a ton for the offer! I'll go through the motor I bought and if anything's missing or damaged I'll reach out. It came off a running totaled truck, so I don't think I'll have to do much - but it's good to have a source of parts just in case.

Regarding the flywheel, that's one point I missed in my original post. Both flywheels have notches for the crank position sensor, but the design is different on the V6 vs V8 flywheel (six sets of notches vs eight notches). I'll need to swap to the V8 flywheel to make the truck run right. I have the engine and a 5.2 4x4 MT PCM, so I just need the clutch, flywheel, pilot bushing, throwout bearing, plenum gasket, camshaft position sensor, injector plugs (if you have any of those let me know), and fluids.

Now's a good time to talk efan swap too! I'll be using the following setup:

Flex-a-lite 16" 2200cfm fan: https://www.summitracing.com/parts/flx-105387
Flex-a-lite Adjustable fan controller: https://www.summitracing.com/parts/flx-121281
Inline sensor bung: https://www.amazon.com/dp/B018FY12CW/

I know I said I wanted to use an OEM fan, but after thinking it through I'd rather use new hardware (the mounting should be easier too). I've got plenty of scrap metal (including some 22ga sheets) to build a custom bracket and shroud for the fan. If this works well on my 94, I may do the exact same efan swap on my 02.
i don't have any of the manual trans stuff but i do have the inj plugs as a matter of fact you could have the whole wiring harness and pcm all mine are carbed but you do have something i need . I have a 97 tj jeep and i want to put my 360 out of my rv in it but i need a bell housing off of a dakota to match to my trans so do you have an extra bellhousing????
Thank you a ton for the offer! I'll go through the motor I bought and if anything's missing or damaged I'll reach out. It came off a running totaled truck, so I don't think I'll have to do much - but it's good to have a source of parts just in case.

Regarding the flywheel, that's one point I missed in my original post. Both flywheels have notches for the crank position sensor, but the design is different on the V6 vs V8 flywheel (six sets of notches vs eight notches). I'll need to swap to the V8 flywheel to make the truck run right. I have the engine and a 5.2 4x4 MT PCM, so I just need the clutch, flywheel, pilot bushing, throwout bearing, plenum gasket, camshaft position sensor, injector plugs (if you have any of those let me know), and fluids.

Now's a good time to talk efan swap too! I'll be using the following setup:

Flex-a-lite 16" 2200cfm fan: https://www.summitracing.com/parts/flx-105387
Flex-a-lite Adjustable fan controller: https://www.summitracing.com/parts/flx-121281
Inline sensor bung: https://www.amazon.com/dp/B018FY12CW/

I know I said I wanted to use an OEM fan, but after thinking it through I'd rather use new hardware (the mounting should be easier too). I've got plenty of scrap metal (including some 22ga sheets) to build a custom bracket and shroud for the fan. If this works well on my 94, I may do the exact same efan swap on my 02.
i put an electric and a 4 core rad in my 88 3.9 i changed the fan 3 times and it still gets to hot with the ac on in stop and go traffic let me know if it works i nput a hayden on and it wasn't much better than the cheap one. So i'm going dual fan with custom shroud when i put the magnum in it .(y)
i put an electric and a 4 core rad in my 88 3.9 i changed the fan 3 times and it still gets to hot with the ac on in stop and go traffic let me know if it works i nput a hayden on and it wasn't much better than the cheap one. So i'm going dual fan with custom shroud when i put the magnum in it .(y)
hell you can have the inj and the plent i'm just keepin the motor for my 89 ram 2500 throttle body and granny gear it gets 21mpg but it's so ugly my kids won't ride in it ( a tree fell on the cab) but i couldn't bel the fuel mileage it gets amazing!
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Unfortunately I don't have an extra bellhousing, I'm sticking with the AX15 that came in my 94 so I'll need that bellhousing for my build. The AX15 should hold up to the 5.2 (I'm not doing any racing or offroading, more of a trash and slash truck) but if it ever fails I'll swap in a NV3500 and I'll save that bellhousing for you.




How big was your fan? I'm going with a 16" that should move over 2200cfm, 2000cfm seems to be the recommended threshold for a stock 5.2 so I think that would be fine. I'm surprised you had overheating issues with an efan on the 3.9, unless it was a much smaller or worse-flowing fan?

I have an old data logger I may adapt and put on the truck before and after the swap to track temps, I'll let you know if I do that. That would give me concrete info on how well the electric fan worlks. I'll try logging:

1. 3.9 with clutch fan
2. 3.9 with efan
3. 5.2 with efan




That's fantastic mileage! I can relate on my truck, everyone in the house thinks it's cool but nobody wants to be seen in it haha. I'm only getting about 18 in my 94 with the 3.9 right now, but all my driving is short trips around town.

If you want to send those parts my way I could definitely use the harness, that would probably be just as fast as repinning my existing harness and then I could swap back to the 3.9 easily if needed. I just picked up a PCM but I have no way to test it until I get the swap done, so an extra would also be handy for testing. Shoot me a DM and we can work something out!
ok i sent you a mess
Try using a fan off a crown vic. Cheap and effective. They move a lot of air and are usually readily available for cheap at junkyards.
thanks for the fan info i'm not a ford guy do ya know about what year crown vic so i can make sure my salvage yard has one ???
Looks like that's the fan for a 2006-2011 Crown Vic, if that helps. I'm no expert, just peeked at the compatibility list at that link (there are some Lincoln and Mercury models which use that fan as well).

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