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91 318 to 98 5.9 swap

4K views 32 replies 6 participants last post by  DionR 
#1 ·
I've got a 91 Dakota 4WD with the 318 TBI motor in it with 220K miles. Not only is the motor getting long in the tooth, but it didn't start out as the best when compared to a Magnum. So, decided I would do a Magnum swap and improve it both in wear and design.

When I bought the motor, I though it would be as simple as using a 93 Ram PCM to run the 5.9 with a 92 Dakota engine compartment harness. Then I discovered that the Rams went to a 3 wire speed sensor in 93 while the Dakota's waited until 94. Add to that, the Ram had two O2 sensors while the Dakota only one. Now, neither of these is all that hard to figure out, unless I am missing something.

My plan is to:

1. Rewire the harness to use a 3 wire speed sensor by splicing in a sensor feed from the CPS. The other wires should be good to go.

2. Splice a wire into the speed sensor wire circuit and run it to the bulkhead connector and into the cab and up to the instrument cluster.

3. Re-pin the instrument cluster plugs to match a 94-95 instrument cluster and swap in an electronic speedo cluster.

4. Splice in a second O2 sensor plug and run a wire back to the PCM.

I have an early return style fuel rail, so I think fuel is covered, plus most of the rest of the OBD1 stuff (intake, TB, exhaust manifold, etc.) minus the 5.9 injectors.

I have printouts of the wiring, still working on verifying everything though.

My question is...what don't I know I don't know? Am I missing something that will make this a huge science project? Am I correct that the engine compartment harness from the 92 should plug into my 91 without issues?

Been all over the internet looking for a similar swap and came up blank so thought I would ask.

Thanks.
 
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#2 ·
Since the donor motor is a OBDII generation motor, that's why it has two O2 sensors for it. I'd grab some 1996 parts (Y pipe, intake, exhaust manifolds; wiring; ECU).

The other choice is to grab a 92/95 OBDI harness and ECU and work off of those, IMO.

I'm not sure if the engine bay wiring plugs right in; I'd want to cross between the 92 and 91 factory service manuals. They'll be CLOSE in any case.

RwP
 
#5 ·
Since the donor motor is a OBDII generation motor, that's why it has two O2 sensors for it. I'd grab some 1996 parts (Y pipe, intake, exhaust manifolds; wiring; ECU).
After some investigation, I believe the only time a 94/95 5.9 has two O2 sensors is when it is an HD motor. Looks like most of them are just a single O2 sensor like my '91 and the '92 harness I have.

The other choice is to grab a 92/95 OBDI harness and ECU and work off of those, IMO.
That's what I did. Grabbed a harness off a '92, as well as the manifolds and y-pipe. Also found a ECM from a '94 van for a 5.9 that looks to be a direct plug in (pin to pin) minus the possibility that because the van harness doesn't include a tach wire the ECM might not have a tach output, and the '92 harness is missing the 3 wire speed sensor input.

I'm not sure if the engine bay wiring plugs right in; I'd want to cross between the 92 and 91 factory service manuals. They'll be CLOSE in any case.
Been a little while since I compared them, but going off my memory, the harnesses swap fine. I have some wires for fog lights that are missing from the '92 harness because I think the Sport with the fog lights was a 1 year only deal.
 
#6 ·
Weights are on the flexplate, and the 5.9 I bought came with one, so I should be good to go as far as the balance is concerned.

Truck has the A500/42RH with lockup right now. Tranni has a 1-2 flair when it is cold, so I am expecting to do some transmission work when I do the swap.
 
#4 · (Edited)
Test

Cool!! I can respond now. I responded to RalphP the same day he post, or at least the next day, and got a response that my limited posts meant I had to have it verified by an moderator and never saw it show up. Even sent a message and didn't hear back.
 
#7 ·
Oh, and I ended up with a '98 5.9 OBD2 motor, but plan to swap sensors and injectors to a 94/95 OBD1 setup. Probably swap the intake at the same time so I can run the EGR valve and avoid lighting up the check engine light.
 
#8 ·
You can do most of the tranny yourself except for the OD spring without some help
rebuilding
is the A 500 original?
your 91 318 has an a-500 my 92 has a 518
a 500's came with various numbers of clutches (especially 4 cyl so upgrade to more (there may be two snap ring slots in the shell)
or get an A998/A999 core and get even more
any number of clutches can be made to hold more lasts longer
you have a 4wd do you can't put the whole A999 trans in like you could a non 4wd and the dbl wrap band will not work on most (or any) a500 I've worked with) (comments from trans experts welcome) but your 4wd may be using the case with the holder for the dbl wrap band IDK
dbl wrap band gives you more hold in manual low and reverse if you are doing activities that require more hold
use atf+4 it's good stuff only better is Citgo Quatrosyn
 
#9 ·
is the A 500 original?
Pretty certain the A500 is not original to the truck. I have seen JY paint pen marks on it.

Truck led a pretty hard life before me. When I got it the rear diff was exploded, front diff was gone and only the stubs in the spindles left, TC had been swapped to some late 80's unit and the motor had to come out to replace the rear freeze plugs that had been replaced by rubber squeeze ones (mucked out several inches of stop leak out of the block when I did that). Didn't check the numbers, but pretty sure the only original piece of the drivetrain left is the motor, and I am working on swapping that.

So, based on how the truck was beat up, and the paint pen numbers I saw, I am concluding that the trans is not original.

No idea what it should have come with, either.

My plans are just to drive this thing. Makes a decent winter rig, and parts hauler, but not looking for a hot rod. Only putting a 5.9 in it because that is what I found, would have been more than happy with a 5.2. So, whatever I do to the trans will be to fix it, no plans for any real upgrades.
 
#10 ·
check your vin for oem trans and chk build sheet for trans and diffs
check the vin on the trans
if you are unlucky it will be a V6 trans ):
just build stock
put in as many clutches as your sell will hold with the snap ring all the way out
of no out to the end snap ring groove get a different shell they are cheap
inspect the planetary trust washers in the od closely
doing the cooling upgrades can be cheap
find a big Ford cooler at the wrecking yard and some half inch hose

run 0W x oil
fullsnthetic is inexpensive at wally world
 
#11 ·
I know it's been a year, but this isn't dead. Thought I could build a pole building shop by myself last summer and get the motor swapped after that, all before winter hit. Still working on building the shop......

I had started looking for a 5.2 PCM so I could sidestep the dash/VSS issue as I had heard that the 5.2 PCM would run the 5.9 ok. This would save me doing a bunch of rewiring to get a working speedometer making the swap that much easier. I figured that if the 5.9 ran ok on the 5.2 PCM, then I would leave it alone, but if not then I wasn't out anything but the cost of the PCM.

But recently I tripped over this info. Looks like a 2 wire speed sensor should still work on a 3 wire system. Sounds like the VSS pin on the PCM is powered and if you wire it to a ground through the 2 wire sensor, it will function just like it did using the hall effect 3 wire sensor. Only downside (I can see) is that the 2 wire sensor is probably mechanical in nature which means it will wear out while the hall effect sensor probably didn't have any moving parts and might last longer.

If so, this means I don't need to add a wire for the 3 wire sensor, nor run a wire into the cab for it and I don't have to rewire my dash for the '94 Dakota IP. And I can run the PCM I have that already matches the size of the motor.

So I might already have almost all the stuff I need to make this kind of plug and play. Now I just need to time to get moving on it.
 
#12 ·
I know it's been awhile, but I haven't given up. Was going over the wiring again, updating my notes and thought I should comment here just so the thread is kept kind of alive.

Biggest issue I have run into recently is the need for a radiator and with the shipping issues, seems no one has one in stock. Hoping to find a decent one at the JY.

The other thing I have worked on is the accessory drive setup. The 91 318 used a different power steering pump than the later Dakota and Ram, one that bolts to a wing on the timing chain cover. I am going to swap my original TC cover onto the 5.9 so I can use the current pump. This brings up the question of an alternator mount (I don't have AC) and will the existing one put the alternator in the wrong place and interfere with anything. I suspect it will so I snagged an alt only bracket from a Magnum motor and it appears that should bolt up to the TC just fine. Feeling like that is solved.

I think the only thing standing in my way (besides parts shortages) is getting off my duff and doing the swap.
 
#14 ·
Just a quick update, if for no other reason than to keep the info documented.

Motor is almost together and making plans to get this done soon.

The other thing I have worked on is the accessory drive setup. The 91 318 used a different power steering pump than the later Dakota and Ram, one that bolts to a wing on the timing chain cover. I am going to swap my original TC cover onto the 5.9 so I can use the current pump. This brings up the question of an alternator mount (I don't have AC) and will the existing one put the alternator in the wrong place and interfere with anything. I suspect it will so I snagged an alt only bracket from a Magnum motor and it appears that should bolt up to the TC just fine. Feeling like that is solved.
Ended up not using the '91 timing chain cover. The '91 Dakota and '93-9x Grand Cherokee use the same PS pump so I used the '98 TC cover and grabbed a GC power steering mount bracket. Time will tell if it work.

The fan shroud changed between the '91 and '92 Dakota so need to source one of those.
 
#13 ·
Well shoot, still another year down and no swap. I am still moving forward, putting the motor together and such, but not going to happen until next spring as I need it for winter driving.

I need to fix a thermostat housing leak, so will probably swap the Magnum radiator in to fix that leak at the same time. Plus the belt tensioner looks to be on it's last legs again, so will probably swap in one from a Taurus just to keep it simple.

Don't expect anyone cares, but makes me feel better that I am updating the thread.
 
#15 ·
For anyone that cares, 318 TBI is out of the truck and making progress on my swap.

Couple of things I've discovered or changed.

1. Decided to use a Ram/Dakota PS pump. The current pump has a narrower belt and even if I swapped the pulley it would require a non-standard length belt. Using the regular pump means a standard belt.

2. The throttle pedal is different between the '91 and '92. The '91 uses a removable "keeper" while the '92 uses a slot and a "keeper" that is part of the cable. Plus, the mount for the pedal is different. The '91 bolts through the firewall while the '92 is on studs welded to the firewall, and the bolt pattern is different. Still investigating if I could use the '91 keeper and '92 cable. Otherwise I will use bolts and nuts to stand the '92 pedal off the firewall and drill a new hole in the pedal mount to match the firewall.

3. The transmission dipstick tube is different and the '91 dipstick supposedly won't clear the Magnum manifolds.
 
#16 ·
well if you can figure out what plug on the harness was for the second o2 its likely just a cat monitoring sensor and can be ignored and just tuned out later. at this point in your shot at Guinness record longest motor swap im not 100% if your planning on trying to make the 318 tbi run the 5.9 mpfi engine or what. at this point i would have just tossed the engine in stuck a fuel pressure regulator on it and tossed a carb on it. jokes aside im not sure if your going for cleanest swap possible or just over complicating the swap. ive honestly glanced over this post due to the initial post was 2018 figured it was just a revived thread i am curious what your end plan is.
 
#17 · (Edited)
well if you can figure out what plug on the harness was for the second o2 its likely just a cat monitoring sensor and can be ignored and just tuned out later.
Post #5

"After some investigation, I believe the only time a 94/95 5.9 has two O2 sensors is when it is an HD motor. Looks like most of them are just a single O2 sensor like my '91 and the '92 harness I have. "

at this point in your shot at Guinness record longest motor swap im not 100% if your planning on trying to make the 318 tbi run the 5.9 mpfi engine or what. at this point i would have just tossed the engine in stuck a fuel pressure regulator on it and tossed a carb on it.
Valid point, I have no excuse.

I've had the truck for maybe 20 years, and being a 4WD it was a necessity that it was usable for winter. Getting a motor together has been a bit of a hassle, and then there is life and other projects like building a garage and making plans to swap a 5.7/T56 into my Duster. But either way, this has taken way too long.

jokes aside im not sure if your going for cleanest swap possible or just over complicating the swap.
Not going for the cleanest swap. I could wish. Just slow progress at gathering parts and doing my best to make sure I knew about any stumbling blocks before I took the truck off the road. I don't have the luxury of a year long swap, truck needs to be down for only a reasonable length of time.

ive honestly glanced over this post due to the initial post was 2018 figured it was just a revived thread i am curious what your end plan is.
End goal is basically just as if it was a '92 with a 5.2. The end result is off a little in that instead of finding a 5.2 to build I bought a 5.9 instead. Not my plan, truck isn't going to be a hot rod. But that's what ended up going into it.

I started this thread hoping to get insight into what I didn't know about the swap. Based on the very limited responses (even at the beginning) and issues with the website (8 months before I could reply??), I decided to just use the thread to document my findings and experience. Didn't intend or expect it to be 5 years though.

Motor is in the truck, but only bolted up to the trans and motor mounts. But if it makes you feel better, the project is on the home stretch and should run in a week or so barring any unforeseen issues. Either way, makes me feel better. ;)

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#18 ·
After reviewing this thread, I see that I haven't commented on the fuel complications my 5.9 causes.

The 92-'93 5.2 used a return style system with a FPR on the fuel rail. When the 5.9 was released in '93, it was never put in a rig with a return style system, they were always returnless with a FPR on the fuel pump. This posed a problem for me as the fuel system in my truck had the return style and I wasn't real keen on swapping my entire fuel system to a '94+ setup.

The issue that this presents is that the '94 5.9 PCM I am running expects a constant 35-45 psi fuel pressure while the return system will have an approximate pressure of 21-39 psi depending on engine vacuum. Run the 5.9 PCM on the stock setup and it will be severely under fueled at high vacuum conditions.

The easy fix? Don't hook vacuum up to the FPR on the fuel rail. Boom, constant 39 psi fuel pressure right in the middle of the expected range.

In regards to the fuel pump and lines, the '91 Dakota uses the same pump as the '92-'93 so no change needed there. The fuel lines at the motor need to be swapped though, which was easy enough to do. Just have to get them from a JY as I couldn't find anyone selling them new.
 
#19 ·
while you had all this time have you taken the intake manifold off that 5.9 to check the lower plenum gasket? ive never had one with the issue but the main seals "supposedly" like to leak. i haven't had a project drag out for as long as your but my projects always take longer than they should due to lack of free time so cant really fault you there more of a wow factor your still moving along and haven't just given up and bought a different truck.
 
#20 ·
while you had all this time have you taken the intake manifold off that 5.9 to check the lower plenum gasket? ive never had one with the issue but the main seals "supposedly" like to leak.
Effectively, yes.

The 5.9 I started with was a '98 so it had an OBD2 intake on it which got swapped for an OBD1 intake that had been sitting around for awhile. The OBD1 intake got cleaned up and resealed. I did not use the Hughes aluminum plate though, so time will tell if that works out for me.

The original 5.9 was kind of rough, so I ended up getting a different 5.9. That one was even rougher, so I went back to the first one. It got new rod and main bearings, oil pump and even a windage tray I had laying around before a Dakota oil pan with a new gasket. Swapped the cam as it was showing wear and looked to be starting to fail and added a new timing chain at the same time. Heads were (are?) an issue as the local shop refuses to rebuild them and will only swap parts onto new casting for $700. So I scrounged what appeared to be decent heads and put valve seals in them myself. Cleaned up some '94 5.9 injectors by pressurizing the fuel rail and pulsing some Seafoam through them. Added all new sensors outside of the TB ones.

So not a rebuild, but better than just dragging something home and dropping it in. Time will tell if I threw money away putting new parts on this motor.

Getting a motor together was one of the bigger delays on this. I bought what was told to me was a "good running" 5.9, but when I did a compression test it couldn't have run that well. This lead to more discoveries and resulted in me dragging my feet while I tried to decided full rebuild, partial rebuild or different motor.

i haven't had a project drag out for as long as your but my projects always take longer than they should due to lack of free time so cant really fault you there more of a wow factor your still moving along and haven't just given up and bought a different truck.
The fact that truck ran well enough to be useful kept it in the stable and made it easier for the project to drag out. If it was my main project, or if I had to have it running fast, it might have been different. And buying a different truck would take money away from my Duster. :D

Besides, where else am I going to buy a Dakota with a FT transfer case?

One of the reasons I think we see so many major projects like this start and then fade away is because people go into them without a clear idea of what they are getting into. While I knew I wasn't going to know every issue before I started, I figured getting as many ducks in a row as possible before starting the project would make it more likely to actually be completed.
 
#21 ·
i have started a few projects and dumped them but i knew from the start it was going to be a 50/50. wifes mountaineer needed timing chain tensioners. i could just buy another mountaineer for the cost of a known good engine so i opted to attempt to do a bare minimum repair so i could scoop up a cheap motor and rebuild it. numerous chains on that version of the 4.0 and just putting tension on the other ones so i could remove the bad side broke 2 others so i called it then. the one chain is on the back of the engine and requires the removal of the engine to do 100%.
 
#27 ·
Follow up on the balance question. Got to wondering if I could have used a '95 5.9 flexplate and avoided having to slot a hole. Here is what I believe are the facts.

It appears that for the '92-95 MY, Mopar used the same flexplate for both the 5.9 (after '93) and the 5.2 and put the weight on the TC if required. In '96, they standardized the TC, made the bolt pattern symmetrical and added the weight to the flexplate.

So, there appears to be a couple of options to making this all work for a 5.9.

1. Run a neutral balance '95 or older TC and a '96+ flexplate. Requires slotting a hole in the flexplate.
2. Run a TC with the weight for a 5.9 and a '92-95 5.2 flexplate without a weight. Bolts together like it was factory (because it is). Note that one hole is offset in this setup.
3. Run a '96+ TC and flexplate. No idea if a '96+ TC works in a '95 and down transmission though, but if you are working with a '96+ transmission this is the factory setup. Symmetrical bolt pattern.

For me, the easy (cheap) button was #1 as I didn't have to buy a new TC.

If I had started with a '95 or older 5.9 TC (or bought a new one) I would have had to track down a 5.2 flexplate to match the offset bolt pattern. But this would have dodge slotting a hole.
 
#28 ·
I am calling it done.

Had to buy a replacement PCM as the used one I had was overcharging.

Had a pretty good exhaust leak due to a crack in the EGR tube. Fixed that and a coolant leak and time to drive and see if anything else pops up.

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Only weird thing is OD. Seems like the '94 van PCM has OD turned off as a default, so I have to "engage" OD each time I start the truck. And the OD button on the van must be a momentary button while my my Dakota has a button that catches. So I have to hit the button twice, once to latch the button and another to release it, and then OD will engage like normal until I turn the truck off. Not convenient, but at least OD works.

And even though the van uses a 3 wire VSS sensor, cruise control works just fine. I just plugged in the 2 wire VSS with a cable pass through and plugged in the PCM. No wiring changes were required, the 2 wire VSS appears to work fine with the later PCM that had a 3 wire VSS. That was a big unknown for me, glad it worked like the link I posted above said it would.

Oh, and even though the van doesn't have a tach or wire on the tach output pin, the tach works fine. I was concerned that the PCM might not output a tach signal since the van didn't need it. My guess was that it wasn't going to be an issue, but I've been wrong before.
 
#33 ·
Follow up on the OD button.

Based on some wiring diagrams, the '91 button is pretty different than the '92-'95. The '91 turns on the "lockout" light itself and has no input from the PCM. And the plug looks like it might be pretty different too.

The '92 engine wiring harness has a wire in cavity 24 of the 50 pin bulkhead connector that runs to the PCM which my '91 dash harness is missing. Not sure how I missed that, but I did. The wire in cavity 24 runs to the OD button and the PCM supplies a ground that turns the light on when OD is disabled (I think).

Not the end of the world, but it explains why the OD light comes on when I push the button and turns off when I push it again, and yet OD toggles from disabled to enabled with each on/off sequence of the button.

This means I will have to add a wire to my dash harness and swap to a later button if I want full functionality. Jury is hung on if I will pursue adding a PCM controlled OD disabled light or not.
 
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