A3 Engine Swap

The rear of the Stretch needed a ICE (infernal combustion engine) to power it on long trips. I put in a A3 engine out of a 97 Jetta, I'm very happy with it aside from all the oil it burns (VW defect).

I wanted to use a 16 Valve GTI motor earlier, but my conversations with people who know have convinced me that the 16V doesn't have enough low end torque to be comfortable in the Vanagon.

The Saturday morning after I picked up the back half I started calling around for a 1.8 GTI engine. I called Bugworld near Sacramento and spoke to Ian. I was looking for an engine that was still in the donor car so I could be sure to get all the small bits to make it work. Ian asked me what I was putting it in and offered several alternatives to the 1.8 including a 2.0 with a 1.8 head, or a stock 1997 Jetta 2.0 liter with a cross flow head and Motronic OBD2 fuel injection. Well the Jetta engine cost a bit more than I was hoping to spend, but I couldn't argue with the logic of getting a nice new clean burning engine, modern fuel injection, an engine with less than 2000 miles on it, and 130 HP with a chip! :-) The 130 hp # is the maximum that I wanted to try to put through a Vanagon transaxle. Ian and the guys pulled a special rush job for me and had most of it out when I got there 3 hours later. I brought the engine and extras home and started to figure out what all the parts were for. Much of this engines smog control was new to me since I stopped working on new VWs about 10 years ago.

Installing the engine:

Click picture for details of dropping the engine in.

With the engine physically in place, it's time for the next least adjustable item;

Click picture for details of making the exhaust

Coolant comes next, a custom 6 outlet manifold for cooling

Click picture for details of coolant hoses

Diesel cruise control comes in handy

Every engine needs a throttle cable, how I did this one

Wire it up and it should run!

How to wire in the OBD2 Motronic system.

Smog parts finally get hooked up.

No room for a battery

Optima to the rescue :-)

OK now it's running, better clean up the intake air.

The Honda air cleaner

The deck lid has a hole that needs fixing

The roast pan from safeway

Time for a test drive

How about 1000 miles including 100 of dirt?


The Swap had been running great for over 1500 miles when my worst fears came true. It stopped running.

I ran the usual checks. No spark. Bentley told me to look for a pulsing LED test light on the coil signal lead/ A-OK, must be the coil. But Why? This engine (and coil) had fewer than 4000 original miles on it. I got a quote on the coil for about $120. This was reason enough to check some more, the sudden way it died sure seemed like a wiring problem. I put the coil on the bench, gave it 12V, ground and grounded the signal connection. Good spark. Hmm, the coil was OK.

Next I put a scope on the output from the ECU, what I saw was not good, a weak square wave centered at about 6 volts with a 2 volt swing. Hmm, I checked the grounds, hoping it would be easy, no luck. I put a 1K pull down resistor to ground to counter the 1k pull-up to 12V in the coil. The waveform got a bit lower and it actually ran a bit, but it died 10 minutes later with even less signal getting to the coil.

Eventually I got around to pulling the ECU open and checking it out. I traced the coil driver lead to a bunch of unmarked SOT-23 surface mount devices (very small) with minimal markings. I poked around with the scope while cranking the engine with the FP relay out to avoid gas flooding. Eventually I found a blown fet that was the output stage. It's a N channel fet with the open drain pulling down the coil signal wire. The source has a 120 Ohm to ground and the gate connects to one of the big brain chips. I found a T0-92 fet and bent the leads to fit, I used a VN2222LL because I has some lying around.

Put it all together and it ran great! It remains to see if it will continue to run reliably.

So why did it happen? I remember when I was putting it all together, I had the grounds and the coil all clipped together with a test lead. Once I pulled the lead off and there was a spark. I had forgotten to turn off the ignition. Shit. Well, I figured it was OK since it still ran. Now I know better. I figure I must have damaged the ECU at that point. 1500 miles later, after heat and hours of use, the fet finally degraded to uselessness. I only hope that was the only hidden damage. I guess only time will tell.

Much later......
The fet blew again. I did some electronics stuff because I was too cheap to buy a new coil. I put a opto-isolater in the circuit and it's run just fine ever since (over 10K miles). I suspect that every now and then the coil gets a internal short where it puts very high voltage on the input lead and blows the fet driving it. The opto seems to be rugged enough to hold up to it, but I keep extra opto's onboard anyway.

Much later still:

The engine now has 80K hard miles on it. Oil consumption has slowly climbed from 1 QT per 1K to 2 QT per 1K miles. Terrible! Soon I hope to put in a TDI engine instead. I've been through about 3 MAF sensors (the trick is to mount them farther from the intake manifold to keep the oil off them) and a few sets of spark plugs. Other than that it has run pretty well.

Here's another A3 Swap page that I've found, this one is in a Scirocco and has a neat table of wiring info!

Last fix 12.14.04



A3 Engine swap

Electric drive

The donors

Cutting up

Putting together

Suspension and Wheels

Interior and Stereo