4.0-2.5 swap

I've gotten myself into a mess on this one. I can't ever tell someone no if it it is possible for me to help and they ask. I'm gonna get over that one day.

My neighbor totalled his 98 with the 2.5 about a year ago. A few months ago he purchased a 98 body that originally had the 4.0 in it and enlisted a mechanic to do the swap for him. Three months have passed and the job is still not done, this is where I come in. He has asked that I take a look see. It seems that it is now running, but very roughly.

here is what I know so far

both bodies are 98 year model
the mechanic did not swap in the 2.5 harness with the engine, and is currently runnning the engine with the 4.0 computer and cutting and splicing the harness as necessary.

My first instinct is to remove any "hack job wiring" and replace the computer and wiring harness altogether with the intact 2.5 units. Does this sound like a winning plan? Are there any differences in chassis wiring that the 4cyl comp will have problems with?

A complete harness and computer sounds like the right way to go to me.

ok he's got a 98 2.5 in a 99 body that originally had the 4.0

Both wiring harnesses are cut, so I told him I didn't want to fool with it. The "mechanic" cut the plug from the 4cyl at the back of the engine and is attempting to splice it into the 6 cyl harness. I don't have the FSM's for those year models, since I own a 97 and a 2000 so figuring out which wire is for would be extraordinarily time consuming.

Would anyone happen to have the color break down of those wires and plugs?

It's been butchered! It's probably running like crap because the ignition and injector timing is totally out to lunch. If the computer from the 2.5l has the same connector, you might be able to swap the computers. Depending on how the wiring was butchered that might fix the timing problem. I suspect your 97 FSM would have the correct wiring diagrams.

Still what a freaking mess. Good luck. At least you know which mechanic to avoid in the future.

is this a joke? a mechanic did this?
WOW
That has to be a mess, IF I were you I would have to tell him that I cant help, but if you are a super nice guy........you COULD spend your afternoons tracing the hack wiring, or just for sheer luck Id toss in the 4CYL computer, to see if by any chance he had it half right, but that would kinda oblige you to finish.
Tuff call

Tell him to cut his losses, take it home, call the BBB on the "mechanic.":repair:

Have him find a new complete, un-butchered, 2.5 harness. (Salvage yard, parting out)

He does not need the computer, he already has one. If he plugs his good computer into the shade tree patched together harness it may go up in smoke. assgas:

DesertYJ said:

Tell him to cut his losses, take it home, call the BBB on the "mechanic.":repair:

Have him find a new complete, un-butchered, 2.5 harness. (Salvage yard, parting out)

He does not need the computer, he already has one. If he plugs his good computer into the shade tree patched together harness it may go up in smoke. assgas:

Click to expand...

Those were my thoughts but the guy is really just a radiator repairman, you should have seen the shop, tools everywhere, there's no way he can find what he's lookin for in there. Besides I think the guy whose jeep it is isn't tellin me the whole story. I keep gettin bits and pieces, and none of them seem to match up.

The liquid electrical tape covering a nest of hand twisted wires was a big clue to not go to that guy, along with the fact that he left his tools lying around inside and OUTSIDE. I played with it a bit to see what he had so far. The IAC is non operational at this point, the fan shroud was hitting the fan, the gas tank was bone dry and the fuel in the line was stale, I got it to idle, but only by mediating the throttle by hand, or creating a massive vaccum leak, no revving is possible, and if it goes over 500 RPM it backfires through the TB then sputters out.

I kinda feel sorry for the guy who owns the thing, but he was just looking for a super cheap fix, and now has a 4cyl 4 door with 3.55 gears that won't run because he dumped on a "friend" of his who said he could fix it for cheap. So it is mostly his fault for being ignorant, Oh and it has been at the shop since march.

Update....It's in my driveway as of this afternoon......the "mechanic"......wow.

The muffler and catalytic converter are painted silver, the tranny crossmember was just screwed into the frame, the u-joints were halfway tight and the straps were bent, the most lugs on any wheel=3 and none were tight. There was a 19mm ratcheting box-end wrench trapped between the swaybar and the frame. and still with the liquid electrical tape on the wires. One shock with no nut, one shock with a loose nut. The brand new battery is dead. That's just for starters.assgas:

Since he has hacked up both harnesses, and the junkyards around here want 300 bucks for a used one, I will be piecing it together which shouldn't be a problem since most of the 4cyl harness is there as a reference. I don't understand why the guy didn't just LOOK to see where the wires went instead of just twisting them all somewhere and giving it a shot. Total idiot, and his kid who was there giving me lip almost caught a steel toe to the pecker while I was under the damn thing. I'll be busy for a day or 2.


To think, I was going to install my lebaron hood vents this afternoon. On the plus side, there are 4 xj's and an early bronco at my house:guitar: .

you are a brave man, wot a challenge, but imagine how proud you will be when your neighbour gets it back running. sounds like you have what it takes so get stuck in to it and please post the pics

good luck Ewen

thanks a crazy story... good luck!

ok I need someone with a 98 model with a 4cylinder or the appropriate FSM to tell me where the following wires go. They go into the cab and I don't have that portion of the 4cyl harness, I just need to know if they go to the same place as the 6cyl.

Brown with yellow stripe
Brown with green stripe
black with tan stripe
black with red stripe
black

other than those few wires I was able to trace it out and piece it together.
I color matched those wires and I have the following conditions.

Engine turns but:
Fuel pump relay only recieving 2.5 volts when key is on.

No spark.

Oil pressure gauge inoperable.

oh and here is what I started with.



Sorry for the poor image quality, it was very humid (read 100%) and the camera fogged up the instant I brought it outside.

EDIT: I forgot to ask if the purge solenoid should be constantly clicking while the key is on......should it?

holy goo!!!!!!! they want it to run or be a fireball?

Ok after a fresh start and some quick troubleshooting I got voltage to the fuel pump and coil. I then had it running with a stumbling idle. did a bit of thinking as to what the A-hole mechanic had done before me and decided to swap to the "6-cyl" computer. Nothing, no idle, no spark. So I then pulled the computer from my 97 6cyl jeep, stuck on the 4cyl engine and voila, the exact same stumbling idle of the supposed "4cyl" computer. The stupid mechanic didn't swap computers. He maybe tried the 4cyl comp, didn't get any fire and swapped back to the 6 cyl computer and hoped it would run.

So now the question is, "does anyone have a 98 or 99 model 2.5 computer for sale or trade for a good 99 model 4.0 computer. I tested it in my 97 4.0 and it works great.


Anybody?

old_man said:

A complete harness and computer sounds like the right way to go to me.

Click to expand...

x2

I cannot imagine how the "mechanic" expects to run a 4-cylinder engine with a computer that's looking for 6 cylinders. I would certainly expect that to run "a bit rough."

I finally convinced the guy to get a computer for it, and it fired right up. I started checking subsystems and noticed that there was no PS fluid. I added fluid, worked it in, and then fired it back up. It promptly blew up a PS pump hose fitting and hosed down my brand new deck with Power steering fluid.

The IAC is malfunctioning, and the Vac reservoir is not connected. I get to bleed the brakes as soon as we can fire it up without hosing down the porch.


Question: the dash panel is inoperable, NO BUS. This means that the wires don't go to the same place once they cross the firewall, or that the 4.0 dash panel is not compatible with the 2.5 computer. Does anyone have a clue on this one?


All in all I'm close to getting rid of this thing, but my wifes xj died this morning, and mine keeps trying to overheat. Looks like i am gonna have to add one of my famous aux. radiators.