Grand Cherokee '98 ZJ Diesel Swap (QD32T)

Carnage
Winch master
Posts: 8
Joined: Wed Jun 22, 2016 2:17 pm

Grand Cherokee '98 ZJ Diesel Swap (QD32T)

Postby Carnage » Fri Jul 20, 2018 8:03 am

Hey Guys. I wanted to share with you my build as I got so much help from this forum and I'm sure it could probably help someone who want to try a Diesel Swap on a ZJ.
I just love Jeeps (solid axle mainly) I travel a lot (live on the countryside) so I needed a versatile vehicle that could handle well on heavy dirt/mud as well as on road. I do around 2700 miles a month, and in my country gas has gone quite expensive, so on 2013 I did my First ZJ Diesel Conversion, and truth be told, it was horrible, it was so under power the engine/tranny and gear selection was not right that was really slow, the thing is that it was more expensive for me to try to fix it than to buy a new ZJ and start all over, so on 2015 I got my stuff together and bought a new ZJ to do the Conversion. Right now my fuel economy is around 26 mpg. Now let's get into details of the build:
1-ENGINE: About the engine, a Nissan QD32ETI was chosen, but the Electronic Fuel Pump was swapped for a Mechanical Fuel Pump (from a TD27T with the fuel adjustment tuned for a QD32). You could say the engine it's a QD32T but that's not exactly right.
The mechanical fuel pump was a Zexel 104740-7123, as you can see on the following photo it comes with the Turbo Boost Compensator.
Image
Here is a video of the engine test before reception.
https://www.youtube.com/watch?v=aFSHxhGa8Ec
Here is a pic of the engine test mount.
Image

2-TRANSMISSION: OHH The damn transmission. This was my biggest headache and where I spent most money in total (in the end I spent more money on the transmission that on the engine itself). From my older Swap (manual ZJ) I wanted this swap to be different with an automatic transmission (well actually more of a manumatic) so the chosen transmision was a RE4R01A.
a)The first transmission that I bought was matched from a TD27T engine, actually the RE4R01A 31000-47X11 automatic transmission.
I wrongly assume that all the TD27T mounted transmission would work on my swap, ohh boy I was so wrong, the flywheel was different and because of that the torque converted was also different in order to fit a QD32, also it had the horrible TX11A transfercase, for those that don't know, that transfercase it's vacum actuated. So After I had everything mounted I realized it didn't work, so time to get a new transmission
b)The first transmission that I bought was matched from a QD32ETI (the RE4R01A 31000-4Gx03 transmission), now the problem with this transmission is that the transfer it got was the 4WD ATX14A, that it was competly electronic, so I had to get the TCU for this transmission.
Image
Having everything the mounting was done, and after carefully checking the conection diagrams I realized it would be impossible for me to use the TCU, so I had to configure the TCU in order to have a 50% torque distribution all the time, instead of using the speed difference between the axles as it was designed, so it was actually like a 4HI all the time.
This worked rather well until I broke a U-Joint at 75mph (not funny) I realized that I need to have the ability to swith to 2WD back and forth and this transfer case was not going to work for me. I took the front drive shaft out and didn't worry about it for a whilem as it was 2WD all the time, until I was doing heavy mud driving that it was heating the transmission a lot, sadly I didn't have an independent oil cooler, rather than the radiator/oil cooler combo, the end result, was that water leaked inside the transmission, which evaporate and burned all the seals. After tearing the transsmision apart I realize there was so much to fix as the friction plate where all destroyed that I needed to buy a new transmission.
The thing is that the ATX14A Transfer is a nightmare to wire up and to control, but as you can see in the circuit diagram, I just couldn't easily convert/recreate the signals coming from the ECM (RED)
Image
b)The third transmission I knew exactly what I needed, a RE4R01A transmission with a TX10A transfercase, so I was searching a 31000-4Gx20 that mates to a QD32 engine, but I couldn't find any, so what I did is to get a transmission that the gear ratio was the most similar to the one mated to the QD32ETI, so I got a transmission that was mated to the TD27T the transmission RE4R01A 31000-47x15. As I already knew that I was going to have issues with the mounting, the hydraulic pump was swapped from the second transmission and everything related (bell housing, torque converter, etc). An external oil cooler was also installed, and the transfer case shifter. So far, everything has worked flawlessly for almost 100.000 Km

3-ELECTRONICS: This subject was the most important to have everything working. For me it was most important to leave the original PCM alone and not to cut any original cable so I could adapt it to the new system.
For the transmission I disconnected the Line Pressure Solenoid, thus leaving the transmission with full line pressure (better for the transmission as the friction plates don't slip each other),
people say this produce hard shifting, but as the Jeep is heavy I didn't feel any noticeable hard shifting (and indeed better for the transmission).
For the shifting control I use the Inhibitor Switch because it gave me the exact location of the shifter, (I kept the original ZJ Shifter and I only had to adjust the shifter cable height so both the transmission and the shifter align correctly), that means that I left "1" as First Gear, "2" as Second Gear (First and Second Gear have the Overrun Clutch activated so I had sort of "engine brake", ideal for going downhill) and "D" as Third Gear. For the OverDrive I had to place a switch so it could effectively shift from Third Gear to OverDrive when the shifter was placed on "D".
Now if we check the shift selection of the RE4R01A 31000-4Gx20 transmission.
Image
We can see that the LockUp at full throttle activates almost at the same time as the OverDrive kicks in, and the same goes when it unlocks, so when going out of OverDrive the lockup disengage.
Knowing this I use the same switch to activate/deactivate for the LockUp and the OverDrive
Having all this I enable the Inhibitor Switch so the engine could only turn on when in "Park" and "N", I also used the Inhibitor Switch on "R" to engage the backup lights. I used the original Jeep oil pressure and temperature sensor re-threading them in order to work for the QD32T engine, having them enable I got engine temp and oil pressure back. For the Speedometer I have to use and Speed Corrector because of the transmission gear ratio and the wheels I was getting values too different from the reality.
I haven't got the time to get the Tachometer working, but so far I don't miss it. For the "KickDown", I used the TPS of the QD32T and engage it to the LockUp at full throttle only when on Third Gear.
In order to get the the proper shifts I need to recreate the Relationship between Shift Solenoid and Gears Selection.
Image
As I wrote before I use the Inhibitor Switch to get the "2" and "D" signals
Image
So the only new Signal I needed was the OD that was just an ON/OFF Switch to 12VDC, all the 12VDC mentioned it's just a fused relay to 12 BAT controlled by the ignition switch.
I needed 4 Standard 5 Pin Relay and 1 Standard 4 Pin Relay.
Image
I don't remember if this was exactly how I connected it, but you get the Idea on the Schematic that you can only OD/Lock Up on "D", and that on 1, N, R, P both Solenoid A and B are On.
For starting the Engine I use the Jeep's Original but I had to place a new push button under the start key for the Glow Plugs, so it's really easy to start the engine. If I remember correctly this was the only thing I had to do dealing with the electronics.
Finally this is what the Jeep look so far
Image
Now what I have the most headaches what with the Mechanics Mounting because I had a LOT of work, in another post I will get into more details.
Last edited by Carnage on Tue Aug 13, 2019 6:15 am, edited 1 time in total.

Carnage
Winch master
Posts: 8
Joined: Wed Jun 22, 2016 2:17 pm

Re: Grand Cherokee '98 ZJ Diesel Swap (QD32T)

Postby Carnage » Tue Aug 13, 2019 6:11 am

I'll be posting more info as I get time to do it. It took me much more time to finish than originally expected (took me about 8 month labor)
A few more details about the mechanical changes
1-AXLES I swap the front axle as it was junk, I swap the read axle so it could be a D44A (had years of bad experience on a D35) the axle ratio for both axle is now 3.73
Image
If I had more time I would have swap the Front Axle with an XJ High Pinion D30, with some adjustable lower control arms, but for now it make no sense to make that change.
2-Mounting In order to mount the Gear Box I use the original Gear Box Mounting Support (42RE) and was adapted creating an internal base using the RE4R01A mounting base (like a sandwich) it as work flawlessly.
Image
I had to completely remake the exhaust gas system, I used 2.5" pipes. I had problem with the engine oli filter hiting the frame, so after struggling for a while I found an oli filter that had enough clearance with the frame.
Image
I'll be posting more info the time allows

Carnage
Winch master
Posts: 8
Joined: Wed Jun 22, 2016 2:17 pm

Re: Grand Cherokee '98 ZJ Diesel Swap (QD32T)

Postby Carnage » Sat Nov 23, 2019 4:46 am

Got time to put a little more info
Misc Stuff
a)For the steering fluid reservoir I use one from Nissan Frontier.
Image

You can see in this pic the original diesel filter and fuel pump (From a HYUNDAI/KIA 2.5). The mounting location was horrible and the pump seal was not good enough. I killed 2 pumps before realizing that it was not going to work that way

b)I used a top mounted intercooler again from a Nissan Frontier (YD25 Engine)
Image

4-Fuel Lines
The fuel lineas was truly a PITA!
When I made the first try with the engine just mounted, it was just a mess, a lot of white smoke and had a really hard time getting it to start, it was so long to make it start, that while I was away, someone tried to start the engine and just killed the started motor. As soon as I got that repaired I realize that I wasn't getting enough fuel, so I bought a different elevator pump with water separator. I also mounted a high flow low pressure electric pump, in such a way that the fuel filter was always full, making a new return line from the top of the filter in order to get the excess out of it, so I got 2 return lines, 1 from the engine, and another from this new filter. The good thing about this is that I never had to manually get fuel inside the filter/water separator as now it has an electric fill :lol: as you can see on the following pic.
Image

I learned the hard way that I had to forget about the original fuel lines and just made some new fuel lines just for diesel. After I fixed this I never got again air on my fuel lines

Finally you can check out the final setup came to be.
Image

I must say that the trial period was very frustrating, so frustrating that all I wanted was to throw the Jeep off a cliff :-|, but after taking a brake from it I came to my senses and started working on it again.

Here is a video of the engine mounted and working
https://www.youtube.com/watch?v=qeUPfBJeP4Q

I will be uploading more pics and more info as the times allows

Return to “Projects / Mod's”

Who is online

Users browsing this forum: No registered users and 4 guests