I have a 91 Dakota I just bought with the 5.2 V8 and the truck has a lot of miles on it 240k, at first I was thinking about doing the Magnum on LA block swap with the redrilling but with the miles now I am thinking it makes a lot more sense to just buy a complete used Magnum 5.2, put seals and maybe rings in it and drop it in there instead. Plus I read that if you don't have the magnum piston with the magnum on LA head swap that you don't really get the true magnum performance anyway.

Can anyone tell me if there is a limit on the years of Magnum 5.2's that are going to be a drop strait in swap for this application?

I don't want to convert to a carb, it does not have to be that fast, it's just going to be a nice lowered flat black shop truck but the Magnum makes a good bit more HP than the LA 318.

Or I'm open to other cost effective options for this. I've done lots of engine swaps, supercharger, and turbo stuff before but I don't want this to be a very complicated (or expensive) mission, but I can spend a few bucks on the truck.

Also, does anyone know which Trans this truck has, is it a 42RE or something else? Can a 727 torqueflight drop into this application?

I see 2 possible issues.
1) Somewhere in the early 90s (I believe it was 92 or 93), Dodge changed the motor mounts from the old mounting ears on the block to flat plates with threaded boss in the block. You will need the motor mount brackets for which ever motor your using.
2) I believe the Magnums were all port injected instead of being throttle body like the LAs were. I believe the Magnum was also when Dodge went to the OBD II computer. You may have to upgrade the wiring from OBD I to OBD II. I have no ides what that involves.
I have a 91 Dakota here and its a LA with OBD I and I have a 93 and its a Magnum with OBD II, I'm not sure if the change came in 92 or 93. Gene

If you use the LA intake and distributor is there any reason the OBDI computer wont run the Magnum engine off the factory TBI?

1. Tranny can be anything- 727, 42rh or 46rh. Computer and harness will be designed for 46rh if 4x4, probably 42rh is 2x4.
2. Luckily dodge kept the motor mount ears cast into the block all the way thru 2000 on the 318 and 2003 on the 5.9. Just need the brackets which you should already have on your LA
3. Gotta swap the whole wiring and computer- can't use the TBI stuff. This, exhaust and fuel lines in the toughest part of the swap cause you're dealing with 39 psi now instead of 14.5.
4. OBD II startted in 96. 92-95 parts trucks are your friend- 94-95 computers will run and drive but have an extra circuit which will affect drivability- I'm working on which one it is

Lastly, keep the serpentine drive off the 91!. It was a one year only, 5.2 only, deal and desirable b/c it will bolt to a LA

You will have to do something with the bolt holes in the LA intake manifold that hold it to the heads, the bolts in the heads are in the same location, but at a different angle then they are in the LA heads.

I have to wonder if the port injection is part of the HP bump for the Magnum, though the heads are suppose to be much better. I would think the Magnum would run on the OBDI, might have to use all the LA sensors. Gene

Have you done this swap? You said the hardest part of this swap is the fuel system and exhaust, the magnum MPI uses only 14psi?

What is the easiest solution to fuel system? Does my 91 have a return line? Does the Magnum have a return line? I did a big turbo on an SRT-4 and I got around the no return line situation by mounting a pressure regulator back by the gas tank adding a short return there and it worked fine.

As far as the exhaust, I see that the LA shorty headers are "block hugger" with the collectors in the middle of the header where as the "magnum" headers are laid out more like the stock manifolds with the collectors by the firewall, it seemed to me that the magnum headers would be easier since they are laid out more like the stock LA exhaust system, plus the happen to be CHEAPER. No one makes a simple TRUE dual exhaust for the 91 truck that I can see (at least not for the money I want to spend), everyone uses a single inlet dual outlet muffler to split the exhaust after the converter. I would want to do a TRUE dual exhaust with an H pipe. I am an experience MIG welder so even if I have to fabricate the thing with mandrel bends it's not really a huge problem. Is there anything I'm overlooking about the exhaust? (obviously I assume I need O2 bungs for the OBDII Magnum computer)

Switching to the OBDII computer does not create problems with the 91 transmission?

Does the magnum computer and harness just drop right in? Is things like air conditioning, temp and oil pressure sensors, all that going to be problems? Is there a specific year Magnum donor vehicle that is more desirable than others? Should I be looking to get a magnum engine AND trans to make this easier?

Sorry for all the questions and I appreciate your help.

Magnum engine from 1992-95 are OBD-1 and used a hydraulic 4sp transmission with converter lockup and overdrive toggled on/off with a simple 12v circuit operated by the ECU.

96+ went to a fully electronic transmission and OBD-2 at the same time. For this reason neither the electronics or transmission will swap between 92-95 and 96+.

The BEST thing you could do is swap a 92 dakota engine wiring harness into your 91, and hope and pray the connector at the dash stayed the same. Alternatively you could swap out all the wiring(dash board, lighting, etc) if you wanted to avoid rewiring stuff.

I used a 1995 harness/ecu for my swap, I found the engine wiring harness section is remarkably self-contained once you gut out the lighting, abs, etc. All that's left to hook up is a power, ground and a keyed power. You will need a speed sensor hooked up or you will stall on decel.

The early magnums will want around 35psi of fuel pressure. The TBI's were more like 14 and the 96+ units went to 55 I think. Oblivious to this fact, I first installed a 55psi GM LS-1 fuel pressure regulator/filter because they are easy to retrofit to just about anything. It ran, but rich so I put smaller injectors on to compensate.

The OBD-1 computer doesn't care what transmission you put behind it, so long as its hydraulic. If you put a 3sp behind it, you may get a code for overdrive and lockup circuits open, however it won't affect driveability. I have a stick shift so I found a stick shift ECU for mine so this isn't an issue for me either way. If memory serves, the OBD-1 magnum ecu does have a circuit that tells the ECU if you're in gear or not, however I'm not sure what the function of this is, perhaps to cancel cruise control if you nudge the shifter into neutral?

You will have to transfer over your LA sensors for your dash gauges to work. Also I wouldn't expect the a/c connections to be the same but not sure on that as I don't have a/c in my swap.

Transmission speed sensor
STANDARD MOTOR PRODUCTS SC108
sensor connector
STANDARD MOTOR PRODUCTS SC727

You may, or may not need to change speedometer cable to make it work (depends on what your existing cable is).

nope. as long as you stay with 92/93, it will be plug n play. the gas tank is the same from 91-96, 93-down use the return line, (4 bangers use the exact same pump til 96!) Carter 74654M. 94-up uses a non return system.
use a fuel rail from a 92 or 93 "anything" (full size van, pickup) and a computer from a .'92/93 pickup, van , ramcharger or Dakota with a V8. harness from '92/93 Dakota. there are slight differences in auto vs stick harnesses, like the crank sensor plug is a mirror image between the same truck with an auto vs one with a stick.
I had a 93 that I swaped from auto to stick and used the original computer for the '93/auto trans combo without issue.
Even though 94 and 95 are also OBDI, I experimented with a couple of computers from 94 and 95s and the truck didnt like them. I think they went to a differently calibrated injector when they went returnless in 94.

They still used a speedo cable til (and including) 93, so the speed sensor has a threaded port for the cable as well as a plug for the computer input.
I have had an '89, '90, a 93, 94, and currently have both a 92 and a 96 Dakota and have played with them all extensively except the 96 because I have not had that one yet long enough to be able to, ha ha.

You can tell whether you have a cable or electronic speedo if you know what you are looking at.... the font on the odometer numbers is slightly different between cable driven and electronic driven speedo clusters... having had both (and currently owning one of each) I can see the difference.
yea you can run any trans behind an OBD1 computer and it won't care. If you run a 3 speed auto or a stick, you may get a false code 37 but it won't trip the light. because the computers are programmed to look for the "od engaged" command which a 3 speed auto don't have.... will have no bearing on how it will run.
the other responders to this thread apparently have never messed with doing what you want to do, to one of these trucks..
same things apply to pre 93 vans and pickups too, in fact from the factory they used the same compters respective to engine size and "49 state" vs California" models.

I have never played with a "california equipped" setup so this stuff may not apply to one of those but since Illinois is so far from california, we rarely see those vehicles here.

Great thread, and I'm going to follow along as I am gathering parts to swap a 98 5.9 Magnum into an 88 D100. I have a low mile motor, along with all of the under hood wiring. I need to find a wiring diagram from 98 3500 5.9 Magnum 5 spd truck, so I can try to figure out what I need to make it run. I also need to find out if I need the OBDII port from the same type truck, since I didn't get that. Lots of good info in this thread already!

I figured someone who really knew this swap would show up.

Do you know if Magnum long tube headers will work on a 91 5.2?

I have a 1995 Dakota 5.2 auto 2wd that I want to swap a 1960 Dodge cab onto but want to run the 1995 5.2 EFI and computer in if possible, so I like this thread....... lol

So if you obtain a 92-93 computer, harness, and fuel rail, can you take the magnum donor engine from newer model years with possibly having to harvest some sensor ect from the 92-93? 94+ engines are much more plentiful than 92-93 magnums with reasonable miles...

92-95 magnums are the same. When they went OBD-2 in 96 the sensor connectors all changed but will swap right over. Also the 96+ deleted the intake manifold coolant temp sensor, so that one will need to be drilled/tapped.

I used a 99 engine for my swap and used 95 electronics to run it. Be sure to snag the fuel injectors from whatever donor your harness/ecu comes from.

Sorry for all the questions but how big of a job is the harvesting of a wiring harness out of a vehicle, can you remember what were the biggest challenges of that job? I've done lots of things, rebuilt engines, transmissions, etc, but wiring harnesses I've always tried to stay away from.

What I mean is, without having done one of these, does the engine bay harness have connectors everywhere or are there places that the harness needs to be cut and re-wired into it's new home?

Any tips on what maybe you would do differently today, or tricks? Did you label everything or is it pretty strait forward and obvious?

How did you go about this whole process, did you remove everything like the radiator etc and start with a clean engine bay or did you do it piece by piece replacing the old harness?

I've done many engine swaps but for some reason the minute you add "wiring harness and computer" into the mix I get concerned.

If you use the 92-95 wiring, it's not hard. 96+ when they went OBD-2 is a rats nest, stay away from that one if you're not comfortable with wiring.

I grabbed a 95 harness from a jeep grand cherokee at the junkyard. Start at the engine computer and work your way out from there. The wires go directly from the engine computer to the sensors. Unbolt all your grounds. If memory serves, I disconnected the engine harness at the firewall. The only wires I cut during removal were for the oxygen sensor and speed sensor because the donor vehicle was on the ground with no tires and I couldn't get under it. I had to wire those up after the fact which sucked but at least it was only two sensors. Once you get the harness home you gut out the stuff for the donor vehicle's lighting, horn, starter circuit, windshield wipers, etc. Keep the alternator wires as the EFI computer has voltage regulator built in. You will find the engine control section is pretty self-contained making this part easy. I think the only connector in the whole thing is the one for the fuel injectors. After that it's just putting power, ground and keyed power to the harness to make it run. I installed some fuses too just in case. Also there's a switched ground wire that comes from the ECU to flash back engine codes so you'll want to wire that one up.

I used masking tape and a pen to label what sensor each connector is for. The charcoal cannister purge circuit I removed completely. I kept the cruise control wiring in place but haven't tried hooking it up yet.

To install, I installed my new engine and transmission. Hooked up by rad, exhaust and got all my mechanical work done. Then I took my old wiring harness, gutted out everything except the lighting, windshield wiper, starter and horn circuits and reinstalled it to make sure all that stuff still worked. Then I laid my (now gutted) EFI harness over top and ran the wiring to the sensors, figured out the wire routing and temporary taped the wiring all in place. Then I wired in my fuse holders, ran wires to my constant/keyed 12v sources. After I taped and zip tied everything into it's temporary spots I went to crank. Then key on/off/on/off/on to check codes with the flashing check engine light. Everything looked as expected so hit the key and see what happens. Mine would fire for a second, then die. Eventually I figured out the jeep ecu has security built in. I got an ECU from a Ram, problem solved. Hit the key and she fired right up and purred like a kitten. Then go back, do a final clean up, wrap all the wires together, mount ECU permanently, hang wiring harness on firewall clips, etc.

Yup. another swap I had to do over the years was a 318 Mag from a 94 Dakota into a 97 Ram 1500. I swapped the intake from the 97 with all of its original sensors onto the 94 longblock and it was plug n play. the long block is essentially the same from 92-03. I think 92-93 might have had a slightly warmer cam, but not enough to throw off the computer in any of those years.
some of the other answers in this post are interesting as I have a 80 Volare and a couple of 90s 318s with harness and all, and am looking to cut down a harness to retrofit, that's something I have yet to do, I have one harness from a 92 Dakota and (I think I still have) one from a 97 full size pickup..... I will probably stay with the 92 setup with its OBD1 system as it is slightly less "involved" though they say the OBD II of the '96+ era is more likely to be tuneable, but thats OK because even a stock 318 Mag puts out 2-1/2X the original 90 "rated" HP of the original lazy 6 and that car ran surprisingly well with that motor in place.... not looking to get crazy here/

Yeah the OBD-1 stuff is not tunable whatsoever. The only tune mod I'm aware of is a mopar performance ECU that was offered. In my case, I was replacing a 100hp, bagged out AMC inline 6 in my jeep wrangler so even a stock 5.2 is over double the power.

Do any of you guys know if the OBD2 ECU has to see the Can-bus/gauges to work? If so, is there a fix to not use it? I want to run manual gauges in my old truck, with the sensors the ECU needs to see plumbed in also. I apologize to the OP for the hijack but lots of good info is coming out in this thread.

The www.hotwireauto.com web site has a vary detailed listing of bus-bar /gauges that work, and won't work together. If you understand all that stuff, it is probably great info!
Gene