1999 Jeep TJ Sahara TDI Swap

In the near future I will be swapping the 4.0 Inline from my jeep TJ for a ALH VW diesel. I ended up getting two ALH engines from a Kijiji ad, one was suppose to have internal damage and the other one was ready to run. Using a wiring harness from David Marshall I bench tested the "good one" and it ran well. Turning over the "damaged one" by hand I found that the valves hit the pistons with very little rotation. My initial thought was that the valves were sticking since the engine has been sitting for 3+ years, but after watching the valves move I didn't believe that to be true. I took the timing belt off and rotated the crank and cam together until they came back into sync. I used some primitive tooling to lock the cam and injection pump at TDC, and set the crank at TDC using the harmonic balancer markings since I don't have a VW transmission to work with. The engine came to life very easily once I switched the harness over. I will update as I progress.

Some pictures

Just out of curiosity, is there anything wrong with the 4.0? That engine can give an ALH a run for its money in the longevity department...

Rob Mayercik said:

Just out of curiosity, is there anything wrong with the 4.0? That engine can give an ALH a run for its money in the longevity department...

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Just horrible gas mileage compared to the TDI.

We almost doubled our mileage when I swapped the TDI into our Cherokee.
With a bit of tuning we also have more power than the 4l had.

I pulled my minty 4.0 with only 110k miles on it for an alh with unknown milage. I'm looking forward to doubling the fuel economy...

My 4.0 runs well and it is a great motor, however the fuel economy is that of a full-size truck. I plan to use it for camping and mountain bike trips into B.C and the extra trip range would be very helpful with the added bonus of not hauling extra fuel around. It pains me to tear this jeep apart, but I believe it to be speced well for the tdi engine. It has 3.73 gears and the AX-15 transmission and no A/C. I also rebuilt this jeep from a accident last year and it has become hard to sell rebuilt vehicles for a decent price so I would rather keep it for myself. Basically I want to build a very basic 4x4 that gets decent fuel economy. I would be very happy to get 30mpg with this configuration.

What size tires are you running?
Anything larger than 32's would work better with 4.10 gears.

I would add a 45lb flywheel to the parts list. It makes a big difference in low end power. Nice for slow speed wheeling and even just stop and go in town.

I am running 31in tires, and will most likely stay at this size. Living in Saskatchewan I see mostly flat ground so I will see how this all works out. For now I will probably stay with the stock jeep flywheel based on cost.

I ran my first diesel converted (4bd1t) on 31" tires and 3:73 gears and 27% overdrive. That motor wasn't super happy much above 2200 rpms and i was still easily able to do 65 mph but didn't like to cruise much over.

My last one i used an fj40 with 40% overdrive, 4:11 gears, 33 inch tires and i was still not in a happy range above 65.


Your BHW will have no issues crusing 3000 rpms, i wouldn't wanna cruise much over that, I've never looked into ax15 gearing but im willing to bet you'll be in the 27% range.

The rubber overdrive usually means you'll use 4L more often than you used to when off road but4:10s even on 35s is common. Playing with tire size may be the difference in being happy flowing with traffic or being passed by flowing traffic. You're lucky you have a jeep, jeep lifts are dirt cheap. I consider a 1 inch body lift mandatory for any swapped 4x4, makes linkage adjustments and other items easier to access. Even if you just use hockey pucks, eh? 4 inch lift springs for jeeps are stupid cheap compared to other vehicles.

My pricey ass passat 5 speed flywheel custom built for bhw 5 speed conversions is 35 lbs, you're in a jeep and not an audi so the extra vibes probably won't bother you.

evguy1 said:

Just horrible gas mileage compared to the TDI.

We almost doubled our mileage when I swapped the TDI into our Cherokee.
With a bit of tuning we also have more power than the 4l had.

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Fair enough. Just hate to see a good motor thrown away (especially a 4.0).

This 4.0 will definitely not be scrapped. I have a 1988 Cherokee chief that has a bad motor so it might go into that one. The chief is a automatic and I believe they are harder to swap over to a tdi. I am not really looking for a powerhouse engine out of the tdi, more so this is just a project I've always wanted to do.

You wont be disappointed with the power of a stage 2 BHW. The power to weigh raito is in the favor of the BHW over that of a 4BT which is a very popular jeep swap. It also had a very street friendly rpm range compared to the 700 plus lbs 4bt. I cant think of any advantage the 4bt has over that of a BHW swap other than sound.


Youll lose weight going from the 4.0 to the BHW most likely and double your mpg. That's great both on and off road.

I dont know where you are getting the BHW stuff, it was posted in his first post that he is putting in an ALH....

casey823 said:

I dont know where you are getting the BHW stuff, it was posted in his first post that he is putting in an ALH....

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Perhaps i should use better ventilation while doing fiberglass repair work.

Glad to hear the 4.0 (and the XJ) are getting a second lease on life together to make way for the TDI TJ.

What can I say, I have a bit of a soft spot for the XJ and 4.0...

How far into bc will you be coming? We up a plan a meet up. There's a handful of guys in the Calgary area as well

Nothing planned yet. I have gome as far as whistler last year, but somthing can be arranged to meet up.

The Jeep has been together and running for a couple months now. I have put on about 2000kms with the tdi motor. I have a couple questions:


1. My rad has a overflow/siphon hose, can I tee this into the bleed line on the VW coolant bowl? Or should I run a separate reservoir bottle?

2. Is there any benefit the connecting the VSS sensor to the Jeep transmission.
Maybe there is some idle/vehicle speed compensation feature I am not using?

jason_alh said:

The Jeep has been together and running for a couple months now. I have put on about 2000kms with the tdi motor. I have a couple questions:
1. My rad has a overflow/siphon hose, can I tee this into the bleed line on the VW coolant bowl? Or should I run a separate reservoir bottle?
2. Is there any benefit the connecting the VSS sensor to the Jeep transmission.
Maybe there is some idle/vehicle speed compensation feature I am not using?

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If your overflow hose comes out of the radiator above the pressure relief of the cap, I would think you would put that to a separate (atmospheric) bottle. The VW bowl is pressurized.

The engine software does us the VSS in some of its tuning (unless your tuner removed it). It is also required for cruise control.

I am looking to do some more clean-up on this swap now that I know everything works good and I have driven it some distance.

In particular I would like to get rid of the long upper rad hose by switching it to the passenger side and add stainless exhaust tube in the straight sections where possible. Has anybody connected the bleed line from the back of the head into the upper rad hose? This would also allow me to eliminate the VW expansion tank and only run the jeep atmospheric overflow tank.

At about the 55 second mark is a good shot of what I did and its been on the road for three years with no problems.
https://youtu.be/1tFCPEKhhfw

I ended up keeping the coolant tube on the driver since there appears to be more clearance on that side for the Wrangler TJ. I made one from 1-1/4 steel pipe and drilled and taped for 3/8" NPT fittings. I kept the VW expansion tank since it is easier to fill than the Honda civic radiator I am using. I still don't have an electric fan installed and the temperature does not seem to rise higher than 90 deg C, does anybody else have similar experiences?

I have never heard the fan run on either my JKU or XJ. We just got home from a 250 km day trip in the JKU and the fan never came on once, it was about 23 C out today.

Do you ever pull a trailer with either of your jeeps?

I do not. I have my Dakota / Cummins for that. ;>)
The XJ would have no problems pulling a small trailer but I would not try it with the JKU. If the JKU had 4.10's then it would probably pull a small trailer with a turbo upgrade. It will already over boost on a long hill.

Incase anyone has a similar question; in order to get the factory tachometer working all i have to do is temporarily ground the cam sensor wire that goes to the computer once the engine is running.

I tried wiring a relay that grounds the sensor once the starter is engaged, but it seems that the engine starts too quickly for it to work reliably.

Everyone is aware, the only time electric fans for engine cooling is called for is if there's no airflow to keep temps down with an opened thermostat ... It's the near end fail safe for overheat. If A fan that can't satisfy the system, the next step is the radiator cap starting to open ..... 7? 13psi? Whatever the math is. 250*F?




A thermostat that opens and closes briefly for block/radiator exchange by no means isnt usually enough to trip the fans.

And unless your radiator is terribly clogged for airflow, ripping down the road @ 50 is plenty of airflow...

Fans are usually a sitting in traffic or moving too slow/heavy engine loads situations.


I ran my 09 tdi without electric fans for 3 years. Only time I got it too warm, without boil over, was letting it run, and I ran inside and to poop on a 90f day. Forgot about it.


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What about high water mud and the timing belt have you folks done anything regarding that? Im about to do this swap on a free jeep i got