'01 Audi A4 1.8T quattro TDI Conversion

Consider this the official beginning of my very own TDI conversion thread. I've owned a US-spec 2001 A4 Avant QTM for the last 2 years. It's modified, it's real fast, it's a blast to drive, and it runs great. But it's not a diesel, and I've been a diesel enthusiast for decades. For me, the perfect car is:
- a wagon
- AWD
- manual trans
- a diesel
With this conversion, I'll finally hit all 4 criteria.
Based on the feedback I got on this forum, it seems a BHW TDI would be the easiest transplant, so that's what I've settled on. I bought an entire '05 Passat TDI locally as a donor car. I figure having the entire car will help make the conversion easier. I also bought a bare BHW block and crank, which should make it easy to build up exactly the kind of motor I want.
I've got a few issues to solve:
- I don't want to hack and slash the wiring in my car, so going with a Euro ECU and engine wiring harness is probably best. I need to figure out which Euro A4 would have the closest match for a PD TDI. Any advice in this area would be greatly appreciated.
- I doubt the Passat fuel tank and lines will fit on my A4, so I'll need to get a diesel tank and lines from a euro A4.
- I want proper highway gearing, so that means acquiring a 3.889 transmission and rear end. Either that or I may just get a diesel 6 speed (which usually has 4.11 gearing)
- I'm not sure if the Passat I bought had the gear-drive balance module installed. If not, that's definitely something I want to do.
Beyond those issues, I'm really looking forward to this project! I'll finally have a diesel car to match my diesel pickup truck.

I think you will find that the engine wiring harness will be 99% plug and play into the car at the plenum connectors and t14 near the battery. The fuel tank is the same, just change the lift pump on the passenger side. While you are working the fuel tank remove all the evap crap. The cluster can be an issue, the vw cluster probably wont talk with the Audi chassis modules - just source a TDI a4 cluster. Buy the vw electrical pin removal tool, you are gonna be swapping a lot pins. You will need the Bentley or alldata for both cars.

Sent from my SGH-I777 using Tapatalk

Thanks! It's good to know the fuel system should be transplantable. I was hoping to get a cluster from a UK diesel A4, since they have the same mph/kph setup as US cars. Since I'm a Canadian, I have no trouble reading temperature in celcius I've got limitless access to alldata for any car, so that's not a problem.

Drove my donor car home today. It's almost a shame to pull the engine out of it, the car is in flawless condition. Not a single scratch or dent or speck of rust. It's also clean as a whistle. The only thing wrong with it is someone took all the knobs off the radio (treble, bass, balance, fade, etc). Guess I'll need to find those on eBay or something.
But it won't be a total waste; since the 2005 Passat was available with an AWM 1.8T, and my A4 has an AWM 1.8T, it's dead easy and worthwhile to do a swap between the two cars. Then I can sell the super-clean Passat as a running car and get some of my money back in the process. Win-win!

I'd like to see your progress. I'm located about 30 miles north from Derby Line / Newport.

TDIMeister said:

I'd like to see your progress. I'm located about 30 miles north from Derby Line / Newport.

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Hey, that's only a couple hours from here! I'm originally from Montreal (born and raised), and we just moved to Georgia, VT from Lacolle, QC where we lived for the last 10 years. You're welcome to come by and check it out anytime, but this will be a project I don't plan to finish until at least June or so. I'm taking my time to get all the right parts and do it properly. I'll also be doing some of the work at a shop in South Burlington, VT where they have a bunch of VW-specific tools I can use. I might rent a bay from my buddy there for a week or so for the final stages of the swap.

QuickTD said:

I swapped a BHW and a 5 speed into a AWM 1.8T passat. It is a very complete factory quality swap with fully functioning ABS, traction control and guages. No fault codes in any modules.
Wiring was pretty straightforward. If I can be of assistance, let me know.

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Thanks! That could be a great help. My current plan is for a diesel 6-speed manual with a 3.889 final drive, to get the ratios just right and have a nice low RPM at highway speed (the A4 is a manual already).
Were you able to get cruise control working properly?

QuickTD said:

What is the present trans code? I'd be pretty surprised if it was not a 3.7 final drive, if so you won't need to change the rear diff, just get a euro trans with matching final drive. I would run a 5 speed to be honest, the diesel can pull the gaps and you won't get any taller overall with the 6-speed.

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Not even close, unfortunately. A manual trans A4 1.8T has an 01A transmission with a 4.11 final drive. I already acquired a 3.889 rear end from an automatic 2001 S4, which is a bolt-in replacement. Also has the bonus of 108mm flanges for rear axle shafts, which are more resilient for handling the torque of a modified BHW. A few companies sell upgraded S4 axles that are bolt-in and can take all the beating I'll throw at them.

QuickTD said:

6 speed requires euro only starter, clutch, DMF, trans spacer, subframe, mounts and axles and may require some creativity for the pilot bearing or a manual trans crankshaft with the extra length.

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That may be true for a Passat, but a 6-speed manual is a bolt-in for an A4. The S4 came from the factory with a 6-speed manual (01E), and the mounting points are all the same. Swapping in a 6-speed is fairly common in the B5 A4 community. The diesel 6-speed is also an 01E, it just has different gearing. The only thing I'll need is an S4 driveshaft to go to the rear end.

QuickTD said:

The big parts count on the six speed swap isn't really so much a body fitment problem. The worst of it is more of a BHW engine fitment problem. The passat BHW/01E guys have found it necessary to use the euro DMF and undamped disc clutch due to synchro failures occuring (quickly) when using a heavy 240mm dampened clutch disc. This required a spacer for the trans (bellhousing clearance for the big DMF) and then a euro 6 speed TDI starter to reach the ring gear on the DMF. The spacer then moves the input shaft back so far that it no longer engages the pilot bearing in the short auto crank, making a crank swap or custom pilot bushing necessary.

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That's interesting. So how was the manual trans setup in European cars with a BGW code engine? As far as I know, the only difference between a BHW and a BGW is the lack of a balance shaft module.

I was planning on a single mass flywheel with a sprung hub clutch disc, is that not a viable option with a TDI?

According to Scott Dewitt, my choice of transmission will bolt right up to a BHW without any need for an adapter or spacer or any changes under the car. I'll just need an appropriate flywheel and pressure plate to go along with it. He assures me that a pilot bearing will fit right on a BHW crank without issues. So that's a relief

GoremanX said:

That's interesting. So how was the manual trans setup in European cars with a BGW code engine? As far as I know, the only difference between a BHW and a BGW is the lack of a balance shaft module.

I was planning on a single mass flywheel with a sprung hub clutch disc, is that not a viable option with a TDI?

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I'd avoid a single mass flywheel, as it tends to vibrate 01E synchro rings until they break, which is very strange as the 5 speed 01A uses the same synchros and that trans will tolerate a SMF.

This has all been a lot of text so far, so I figured I'd add some pictures to make the project more real.

Here is the donor Passat GL TDI, which will soon be a Passat GL 1.8T. It has 230k miles (cost: $3950):


The engine with the cover removed:


And the all-important TDI badge :


This is the 3.889 rear end I acquired, out of an automatic 2000 Audi S4, code DXT with just 73k miles (cost: $150):

This is a BHW engine block I got, it came out of a 2004 Passat with 140k miles (cost: $450):


I also got the matching crank and oil pan from the same engine (cost: $300):




Eventually, all that stuff will end up in this car, my pelican blue metallic 2001 Audi A4 Avant 1.8T quattro manual:




Although it really doesn't look all that pretty right now :

oops, I just realized I'll need to get new front springs for my car. I had already bought a full set of springs before planning for this diesel swap, but the front springs I got won't cut it for a TDI

QuickTD said:

I think you'll be pleasantly surprised. I thought the same thing when swapping the diesel into the gasser. I figured it would be sacked out, but it made no difference. Didn't even need to aim the headlights.

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But were you going from a 1.8T or a 2.8 V6?

QuickTD said:

1.8T. The TDI isn't much heavier, if at all. The 1.8T must have at least 100lbs of vacuum hose on it.

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Not mine! I've removed most of that vacuum crap on my engine

But I know what you mean...

I only thought of coil springs because I was moving the BHW engine block around yesterday to take a picture of it, and it occurred to me that this is easily the heaviest 4-cylinder block I've ever lifted. Still can't believe the guy I bought it from was able to send it via UPS...

Watching this. Will be my next project. Crazy that rear diff was only $150 bucks.

bbob203 said:

Crazy that rear diff was only $150 bucks.

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I know, right? It looks brand freaking new! WAY nicer than the one currently in my A4, which is worn and pitted all over. Jerry Brown's Auto Parts recycling centers carries all kinds of stuff for reasonable prices, and they serve the entire northeast. They typically only deliver to mechanic's shops, so I have an arrangement with my mechanic to have stuff delivered to his shop when I order from Jerry Brown's. Shipping cost is FREE because they have scheduled runs to different regions every day of the week.

LOL! One of the first things I noticed when I was looking over the Passat before deciding to buy it is that the coolant is the wrong color. It's beige, looks nothing like G12. The car's been sitting in my driveway for a week now, and in that time, the temperature has dropped to almost -40 a few times. Went to have a look at the engine today, and sure enough, the coolant is frozen into slush.

Guess I'll be doing a coolant flush and oil change ASAP... the used car dealer I bought the car from clearly did a generic fluid swap for the purposes of putting the car on the lot and call it "maintained". Cheap bastards...

OOF. Hopefully it didn't pop a freeze plug.

Ahh you have GOT to be kidding me!!! Nogaro blue is my favorite color of all!!!!!!!!!

Wanna trade when it's done?

Nevah! This color is surprisingly rare considering how fun it is. I really struck gold when I bought this car from a friend of mine 2 years ago. He's been begging me to sell it back to him ever since. Huge seller's remorse.

Just to clarify, someone pointed out to me that my A4 already has a 3.889 final drive ratio, so it was unnecessary for me to get a new rear end. Luckily, it only cost $150, and the rear subframe on my A4 needs replacing anyways, so I may just do some maintenance work to this "new" rear end while it's off the car and put it in my car anyways. Also, this new rear end already has the larger S4 axle flanges installed, so I can more easily put in some aftermarket S4 axles to handle the increased torque of the TDI.

Avoid the traditional inner cv joints. All longitudinal diesels use tripod joints. A4 has 3.89 rear end for the 5 speed manual, but most 01E 6 speeds are 4.11. Also avoid aftermarket axles, most are junk.

Scott_DeWitt said:

Also avoid aftermarket axles, most are junk.

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Really? Even these?

http://store.034motorsport.com/prod...a6-s6/axle-pair-high-strength-b5-s4-rear.html

I was speaking of Chinese axles in the sub $120 price range. I'm not sure about those.

However chances of you making enough torque to break the stock rear axles are slim, plenty of people with over 700 ft/lbs without any rear axle or rear diff issues. Diff also tend to blow before the axles go.

I've got Chinese axles in the sub-$120 range right now I want to replace them. If I'm going to spend money on quality axles, $595 seems reasonable for a pair. Just need to source some proper CV joints to go with them.

GoremanX said:

I've got Chinese axles in the sub-$120 range right now I want to replace them. If I'm going to spend money on quality axles, $595 seems reasonable for a pair. Just need to source some proper CV joints to go with them.

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Best bet is Raxles. You'll be in those axles for over $800 after joints. Raxles can be had for $195.00 each if you have good factory cores.

But to be honest you'll be wasting money on anything more than OE stock axles.

Never heard of Raxles before, certainly worth checking out!

That's the whole point of doing this slowly, getting all the info I need before making final decisions I hadn't made a decision on axles yet, just figured I'd explore the options in the S4 range since those mostly bolt right on.

Would that same diff work in an a6 of the same year? I like the a4 but the a6 is sized more like a passat.

bbob203 said:

Would that same diff work in an a6 of the same year? I like the a4 but the a6 is sized more like a passat.

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No clue. I've owned a C5 A6 tip/2.8 in the past, but I never paid attention to what rear end it used. Also, I'd hardly consider the Passat to be as large as an A6. Sure, it's got a little bit more room inside than an A4 (mostly in the rear leg room department), but I can't splay myself out in the Passat the same way I could in the A6... not even close.