16 Modifications to make the TDI work in the Eurovan

The following are the modifications that need to be made to the Eurovan when using a IZ/AHU engine. These are outside the modifications to the engine and transmission that are detailed on other pages. All together there are quite a number of things that need to be done but if you have the time and patience to do them it results in a very different and very improved vehicle. Others have documented some or all of these changes. Justin at Greaseworks has a blog with more pictures of these steps. His work is very thorough and very professional.

1. Potentiometer installation

The Eurovan uses a cable to link the gas pedal with the intake, the TDI uses electronics. You need to alter the go pedal to make this work. If I were to do it again I would remove the dash to get good access to the location around the steering column where the potentiometer is going to be located. Because I didn't it took a long time and many contortions were necessary to fit the bracket that I adapted from the Passat. Here are some pictures of the installed potentiometer. At the time I did not have access to welding equipment so everything had to be able to bolt together. I cut off the potentiometer mounting bracket used in the Passat and then used a couple of washers and spacers from the hardware store to make the attachment to the stock Eurovan gas pedal be smooth and stable. The main thing is you want to make sure everything lines up exactly right so that there is no chance for binding/wear or for it to jam open or closed.


2. ECU mounting
I decided to mount the ECU in the engine compartment on the passenger side, opposite to where it is in the Eurovan on the driver side near the battery. I did this because this more naturally followed the wiring feed of the Passat, and there was a nice sheltered spot in the far corner of the engine compartment. By switching the mounting bracket around somewhat and drilling a hole in just the right place in the Eurovan engine compartment I was able to secure it far away from any potential rain or splash.


Speaking of the ECU, in order to upgrade to a rocket chip, and in order to be OBDII compliant (for scan gauge or other bluetooth adapter OBDII dongles) I needed to exchange the black 'BK' ECU for a GQ. Found one on ebay for $100 and it works fine.

3. Power Steering
The decision needs to be made whether to modify all the brackets to allow the Eurovan p/s, a/c, etc.. fit on the 1Z engine, or vice versa. From all the reading I did it seemed it was much easier to figure out how to splice in the Eurovan lines into the existing 1Z/AHU components. The most difficult was probably the power steering. Because of the angle that the line comes off the Eurovan is almost exactly 90 degrees different then the 1Z it was impossible to have the Eurovan p/s hoses attach directly to the 1Z p/s pump. To make it work I ended up going down to an a/c shop that did some custom work and had them make me a little elbow from some leftover Passat power steering hose. The solution was to take the old Passat p/s line that had the female end of the banjo bolt along with about six inches of line down to the a/c shop. They cut the old Passat line and nicely fitted a new cap on it so I could attach a banjo bolt through on that end. The result is a power steering line that is well clear of the belts and motor, if a bit exposed to the elements.


4. Air conditioning

The original Eurovan a/c low pressure line very inconventiently stretches across the entire engine in order for it to bend its way down to the compressor. The connections for the Passat a/c compressor are also slightly different than for the Eurovan, so it is necessary to splice the two connections together. Since I knew I was going to have to reroute some lines anyway, after I had everything else in place I took the van to my favorite a/c shop and they quite simply rerouted the line completely out of the way of the engine while splicing the ends of the Passat lines together to the Eurovan lines.

While I was at it I had the a/c shop put in all new o-rings wherever they could find them, and, of course replace the dryer. In the midst of things I discovered the evaporator unit was leaking. This meant taking apart the entire dash to replace or repair it, as it is buried next to the heater core. I found another one and put it in, then had my a/c shop test everything for leaks and charge the system up. After a few months I discovered that the cheap e-bay compressor I ordered quit on me, so I ordered a much better quality one and it has been doing fine in the van.

Since the original MV's had a front and rear a/c blower/evaporator unit one nice part of this conversion is being able to cool down the rear of the van much more quickly than with just the front a/c unit in the Weekender. The blower unit for the rear is in the back right of the van; the duct work all has to be removed for the weekender conversion, but there is copious amounts of cold air that comes from the blower unit in the back and helps cools things down quite nicely.

One other tip: the a/c pressure switch went out on my 93 Eurovan. It was very difficult to find one and when I did the cost was something like $150. For $30 I bought a pressure switch for a 99 Eurovan and then simply modified the wiring to fit the 93 Eurovan. The switch itself is identical.

5. Brake Booster Vacuum Line
I kept the brake booster line from the Passat and eventually had to splice the two lines together as the angle of the Passat did not match up with the Eurovan. The vacuum pump from the Passat has been very adequate for the larger Eurovan braking system.

6. Fuel Pickup, Lines, Filter
The Eurovan fuel pump is located in the fuel pickup assembly inside the fuel tank while the Passat TDI only has a pickup assembly. I think people have gone various routes on this, but I ended up taking the fuel pickup out the Passat fuel tank and adapting it to fit in the Eurovan. The main issue is that the Eurovan's assembly is two part, with the main assembly separated from the top by several inches of rubber tubing. I managed to fix the Passat fuel sender and pickup at the bottom of the Eurovan tank with a plastic ring I glued to the bottom of the tank for stability. I then used the top assembly from the Eurovan to keep the original look and feel.

The Eurovan fuel lines run under the van near the driver and then into the engine compartment on the same side. On the Passat it is reversed. I managed to run the lines across the top of the fuel tank to the passenger side of the vehicle and then along the frame on that side. I attached the fuel filter against the inside of the frame on the passenger side, away from the engine and belts but approximately in the same position as where it was in the Passat.

The fuel tank filler must also be adapted for the larger diesel fuel filler. The tank needs to be removed to get to the insert at the top of the fuel filler pipe. Once it is out the actual removal of the insert is quite easy - just a screw or two and it pops right out.

7. Coolant Hoses
The coolant hoses come into the engine at different angles in the 5 cylinder gas and the AHU engine. You can order the coolant hoses for the ABL engine from Dutch Auto Parts as well to make the job simple. Otherwise you need to mix and match hoses until you find something that works.

8. N75 valve and 50 amp fuse
There are good diagrams of how the TDI vacuum system operates, so you don't have to memorize all the connections before you take it apart. Here is one below. Because of the larger size of the Eurovan the N75 valve could not reach where I wanted it to reach without splicing in some additional wiring. This was the only place in all the wiring where I needed to do this. I mounted the N75 valve along with a bracket to hold the large 50 amp fuse in place.


9. Eurovan Gas to TDI wiring

The part of the conversion I was most fearing was the electrical. I did a few things to overcome my fears. First, I learned how to read a VW electrical schematic from the Bentley manual.The confusing pages of seemingly random numbers and lines and diagrams slowly made sense. It's still nowhere near as clear as a Honda or Toyota service manual, but at least there is logic to the madness. Second, I found a few good diagrams that give the basic schematics for what matters.

http://www.a2resource.com/electrical/CE2.html This is the relay and fuse block information for most V.W.s made in the 1990s, including the A3 Jetta and B4 Passat and T4 Transporter/Eurovan. There are some small differences between vehicles but 90% of what V.W. does for one car it does for another.
Wiring schematic for 98 Jetta AHU TDI. A very helpful resource in color and in one long diagram instead of the very frustrating Bentley diagrams. Note it is for the 98 Jetta AHU, not the 1Z Passat so has some minor differences.
3. I made a
wire by wire comparison of the relevant wiring blocks of the Passat B4 TDI with the Eurovan TDI. There are questions and comments about the wiring in there and is more a draft than a final version. But for those just trying to figure out the basics it is a start.
The ECU pinout from a 1998 Jetta. This is helpful for troubleshooting, but in reality the vast majority of the ECU pinouts are 'self-contained' as they simply go to the various sensors on the engine, as opposed to being spliced into the Eurovan wiring.
Extra Wires from IZ wiring loom

10. Air Intake
I debated using the Eurovan intake and air cleaner but decided against it since it takes up about half the space of the entire engine compartment : > . The Passat intake was also too large and bulky, so I opted to find a A3 Jetta TDI intake at a junk yard and stick it into the space freed up by removing the Eurovan intake. Everything wedged in there just so, and there was room on the far side by the firewall to attach the ECU as well.

11. Intercooler
I first tried using the stock Passat intercooler, attaching it on the Eurovan down close to the horn on the driver's side, but it was so low and obviously in the way that I decided to buy an aftermarket intercooler. I was glad I did. For about $180 on ebay I bought the FMIC and 2" piping. I don't know if it is there anymore, but the title was "
CXRacing Unversal 28" FMIC Turbo Intercooler + 2" Alum Piping Kit for 240SX S13" from 'just-intercoolers.' The installation was quite straightforward. The intercooler itself mounts just under the bumper with a few brackets; the bumper can be cut using a utility knife (in my picture I still need to do some trim work); the piping is a combination of the new piping and the existing Passat intercooler piping from the intake manifold to accommodate a sensor and a vacuum line that are in the stock Passat pipe. I also needed to buy a 1 1/2" to 2" converter to connect from the turbocharger outlet to the intercooler piping. On ebay it was: "1.5" to 2.0" Racing Silicone Hose Reducer Coupler Pipe Turbo 4-Ply 38mm - 51mm 2" from 'qqqusa'. Here are a few pics:




12. Exhaust system
I didn't want to deal at all with the exhaust system. So I simply kept the Passat exhaust back behind the catalytic converter and cut the Eurovan exhaust to a similar point. My local exhaust shop welded the two systems together in no time. I added an extra-long flex pipe, as the Passat flex-pipe is quite short. I decided not to go with a larger exhaust system - the 2" system on the Eurovan and Passat seemed adequate and it has proven fine for the kind of power/performance that I was seeking.

13. Cruise Control
Judging by how difficult the Eurovan cruise control is (and how many problems people seem to have with it), I thought that this would be a large problem. It turned out to be quite easy, with one strange exception I have yet to figure out. On the TDI the speed signal is taken from the ECU so there is simply one wire that basically controls the speed. There are four wires coming out of the left stalk on the Eurovan; these four wires splice directly into the four wires that control the TDI cruise functions, that is part of the TDI wiring harness. The only glitch I've had with mine is that for some inexplicable reason the CC turns itself off when I turn on the right turn signal. Only the right! I don't see anywhere where the turn signal and the CC are connected but for some reason cruise control is cancelled when turning into the right-hand lane.

14. Instrument Cluster
I kept the Passat instrument cluster and swapped it over to the Eurovan. This provided a couple of things:
  • accurate tachometer reading
  • relatively accurate fuel gauge reading (since I also swapped over the fuel sending unit)
  • glow plug light

In the electrical section above there are explanations of how things get arranged, but, in general it is an easy swap. Keep the two wiring looms from the Passat instrument cluster to the relay panel.

Because I have 16" wheels the speedo was considerably off. I also thought my fuel gauge and temp gauge were acting erratically and figured it was the voltage regulator, as
well documented in the TDI Club forums. I sent the cluster off to Derek White at Chubbs Auto in Illinois and he recalibrated it for the new wheel size, a new voltage regulator, and the Passat GLX MFA display option installed. Very good work at a very reasonable price, $110.

15. Brake Pedal and Clutch Pedal Switches
The Eurovan has a complicated system of vacuum lines attached to small switches on the back of the clutch and brake pedal to de-accuate the cruise control. In the 96 Passat the system is entirely free of the vacuum lines, so the brake pedal and clutch pedal switches must be switched over

16. Delete 5th injector on 96 Passat
The 96 Passat has a '5th injector' which squirts diesel directly into the exhaust system for emissions (?). In any case, it was only used on the 1996 and since I upgraded the ECU to one used in 1997 that supports OBDII I also deleted the 5th injector. Good instructions on everything about that delete is