VW R36 Conversion – Mk4 Golf V6 4Motion

r36 in a mk4 golf


I recently had the chance to convert a 2.8 v6 4motion to an r36. The r36 is similar in many respects to the 2.8, both share a near identical block. So physically its not a huge job. Technically however there are vast differences. The 3.6 engine is FSI, and uses a completely different method fuel delivery. Instead of fuel being injected in to the inlet track, fuel is injected directly in to the cylinders just before ignition. This makes the engine very efficient, using less fuel and generating less heat through the combustion process.

I was unfortunate to be given a less than complete engine for the conversion, it was missing several parts, installation had also been attempted before and unfortunately some bizarre modifications had been made to the engine loom which had to be corrected.

Before major work began I logged on to ebay.de and started my hunt for the two major missing pieces. The ECU and most of the wiring loom were missing, so for this engine to have any chance of ever working I would need to find these. I was lucky enough to find an r36 ECU and a complete wiring loom for a passat r36 on ebay so i snapped it up.

I have heard that companies are now starting to produce aftermarket ECUs for FSI engines but for the time being at least the idea was to stick with a stock unit.
It's worth noting that you cannot just plonk on any aftermarket ECU or indeed an ECU from another v6 like the 2.8 the car had originally. Well; you can and a few have, but for that to work you need to go back to a non-FSI setup. There is a nice VW technical manual floating around on the web that goes in to much more detail on the FSI setup. After consulting that I considered it would be unclear how a more traditional setup would fair with these funny shaped pistons, I'm sure it would work but but its likely that it wouldn't be at its most efficient or powerful/reliable.

Box arrives from germany

A couple of days after ordering the loom a large box arrves from germany :) This was great, I now had all the original wiring, and now both looms that plugged in to the ECU. Now with some wiring diagrams I could work out what I needed and what I didn't from this haystack! FYI Most of it ends up in the didn't need pile.

passat loom layed out

With the wiring diagrams i could take each connector check each wire colour and discover its purpose, from there i could then decide if it was required or could be cut away. This involved stripping back all the insulation and removing the unnecssary wiring, otherwise you would end up with a lot of dead weight.

The loom stripped down

So we end up with the above, Note, that this ECU has two big connectors. Each connector attaches to a specific loom. One goes to the engine, and can be left more or less allone. the other interfaces with the car, battery, relays, clocks etc. so you can see the above has alot of coils of cable, these will be cut to lenght and fitted up when the loom is placed in to the car.

On the mk4 there are two main interface locations, one is in the plenim chamber underneath the wiper motor. the other is a 14pin connector behind the batter. wires from this loom will ultimatly end up in one of these locations.

bench testing

Bench testing of the loom to make sure all the power wires, switched and permenent lives had been identified, and a test of the ebay ecu!

vdcs talking to the ecu

Result, it talks to my VDCS so thats a good sign.

I spent many many hours stripping off the loom tape and getting all the wiring I needed, VAG wiring diagrams are really the only way to get this done. Bentley Publishers have these, perhaps talk to your friendly VW technician, even ebay sometimes has these things too. Wiring was by far the biggest part of this conversion, so much so that I would say its unviable for any profit making organisation to do, unless the customer is minted or its a showpeice. As aftermarket becomes more available it would make more sense and is also a nice way to avoid things like the inbuilt immobiliser in the factory ECU, more on that later. Before a single bold was touched on the 4motion, I also bench tested (dining room table(understanding wife)) the ECU (it came from ebay after all!), and it started talking to my VDCS.



r36 fitted with 2.8 accesory system

R36 engine fitted with the 2.8 4moton accessories, after some mods to the bracket.

Once I was fairly happy with the wiring, The next order of the day was to pull out the old 2.8 and really start to compare the two. Again our nice new r36 was missing the ancillary components, tensioner, alternator, a/c compressor, power steering pump and bracket that held all this on. The first thought was that we could just bolt on the old 2.8 ancillaries and bracket. Unfortunately it will not fit without some minor adjustments, this is mainly due to the introduction of a second FSI, lower fuel rail. Its relatively simple to cut away some of top right corner of the bracket to clear the fuel rail, fortunately none of the bracket that is cut is essential. To complicate matters further it also needs to be spaced away from the block by around 8mm, this makes fitting the belt a bit tougher but it looks to be in the limits of the tensioner. If you don't space it off, then the alternator will fowl the injector on the lower fuel rail.



temporary exhaust

R36 with temporary 2.8v6 manifolds, modified to fit and not blow!

The next consideration is the exhaust system, the manifolds from a passat will not fit a mk4. The mk4 v6 manifolds are complicated by a exhaust gas heating system so are also not able to work in standard guise. They are also far too small! However for testing and shake down purposes I had the exhaust preheater channels braised closed then re drilled the holes to fit the new engines stud pattern.

Designs for the manifolds

new manifold cad drawings ready to make up some custom exhaust to get the best flow.

I then designs some new manifold flanges and printed a prototype on my 3D printer. These designs will be used to help create a custom pair of exhaust manifolds and down pipes. However this can be done by a specialist after we make sure everything else works, and the car can be driven there!

3d printed manifold

A 3D printed prototype of a manifold flange. this is worth doing to ensure its perfect before taking to a machine shop. mistakes on the 3d printer are much cheaper!

Clutch gearbox & Water pipes

view of the engine and metal pipes

Simplified water pipe arrangements on the 'rear' of the engine, enables the gear linkages to move.

The 4motion clutch and gearbox will fit directly on to the engine, the block here remains unchanged, clearly uprating this is highly recommended. As the R36 is normally fitted with a DSG gearbox so some modifications need to be made to the cooling system in order for the selector mechanism to move freely. Most of the modifications actually need to be done in any case as a lot of the pipe work is now unnecessary. The main reason for this is the DSG box has cooler, so pipe work for this can be deleted. This required welding up a metal pipe and completely removing the return line, and another metal pipe. Removing the return feed then allows the selector mechanism to move freely.

The R36 is also equipped with an additional cooler located on the near side front wing area. We chose to remove the pipe work for this cooler and see how the temperatures go. Some people in the US actually retrofit additional coolers to some VW's as were in the UK I think we should be ok! But we will know more once we start testing.

Fuel system

fuel filter

A much smaller fsi fuel filter, fuel return is managed from the filter as it has a built in pressure regulator, so a new pipe is linked to the blue return line to the tank.

The fuel delivery system for the FSI engines are very different however a new pump is not required, good news! Correction, we later found at high rpm the stock in tank pump could not keep up with demand so we did change it out for a more powerfull unit. The in tank pump receives demotion, becoming a low (relatively) pressure transfer pump, its also activated only when needed, the ECU has two additional sensors on the engine to detect the pressure in the delivery pipe work. This means there is also only one pipe from the tank to the engine, no return. Instead the FSI return happens at the fuel filter near the tank. Simply replace the fuel filter with a mk5 Golf 2.0 FSI fuel filter and make a small pipe to create the new return. The neat push fit connectors can be reused at each end of this new pipe, from the old return. These new fuel filters have a fuel pressure regulator fitted internally, so if an over pressure occurs fuel flows back to the tank, im not convinced this is entirely required but given the simplicity of the work its well worth doing, the worst case scenario could be an over pressure causing a pipe to pop off or damage to the pump over time.
There is also an electronic fuel pump control unit. This is fitted to the fuel pump at the tank, the metal cover is replaced by a plastic cover with a recess for this small unit. I chose not to wire the fuel gauge through this system, but the pump and ECU communication was wired in as per the passat wiring diagrams.


As I mentioned perviously the ECUs are factory fitted with an ever more complicated immobiliser system, this requires coded keys and clocks to work, good idea in principal I just wish it were compatible with the mk4 system which is similar. We went to Revo in order to get a remap and immobiliser defeat service on the ECU. This wasn't cheep but it did the trick. The fist thing I noticed was I could no longer talk to the ECU via VDCS, to work arround i installed an aditional diagnostic plug, somtihng in the clocks blocks the communications. Although i installed a new plug i left the engine connected to the CAN bus incase it needs to talk to other equipment in the car.

For testing purposes the engine should run without the defeat in place, only for one second or so, still enough time to give it one rev and ensure no nasty banging sounds are coming from within. This was a major consideration in our work, especially as the engine had come from a previous conversion, we didn't want to throw money at it until we knew it was fundamentally sound.

Other considerations

Coolent temperature sensor

The wiring for the coolant temperature gauge needs to be added, this also means the two wire grey sensor needs changing for the green 4 wire sensor. I assume that in the original passat the ECU passes the info on to the clocks via the CAN bus system.

Rad Exit Temperature sensor

To keep the ECU happy we added a coolant sensor on the lower radiator pipe, for this we used an Audi pipe which is a composite of plastic and rubber hose. Unusually this is clipped together with a plastic moulding rather than a removable clip, however it is easy to cut away and replace with a pipe more suitable for the mk4 engine pipework.

Mk5 Rad Fans

The reason for the lower exit sensor is that the newer cars rely on these sensors to activate the radiator fans. I did play with swapping over to a full mk5 style setup. Happily the fan cowling and motors are a direct fit on to the mk4 radiator. However so far it doesn't look like it will be necessary to keep this modification and potentially poses issues for the aircon system. So I have kept with the mk4 setup, I have retained both wiring options so if needs be I can swap it back in.

Activated charcoal canister

The original mk4 charcoal canister was retained, but I chose to use the new r36 solenoid to keep the wiring unmolested. This meant that we had to remove the workings of the mk4 solenoid and basically turn it in to a straight through pipe.


Both engines have 4 lambda probes in the exhaust, the wiring diagrams seem to indicate differences in the main two. So I decided not to use the ones in the 4motion. I did re-use the other two post cat lambdas.

Air Filter box

To maintain that factory appearance, I needed to get an airbox to fit the rather large MAF sensor. The mounting luggs are also flipped, so don't fit the 4motions at all. After closely reviewing another conversion I found that the airbox required was the r32 DSG airbox. Dark side developments had stock so I popped an order in for one.

complete conversion