Project Fox: Does a Jetta Engine Make It Less Horrible?

Update by Tom Suddard to the Volkswagen Fox project car
Jan 30, 2020

It was all going so well. In fact, we’d go as far as to that say our plan was working perfectly. What plan, you ask? Simple:

  1. Try to go wheel-to-wheel racing on as slim a budget as possible. 
  2. Save time and money by purchasing somebody else’s old race car.
  3. Paint the car on a budget to make it look presentable.
  4. Install a full suite of safety gear to keep us safe.
  5. Go racing and enjoy hours of easy, trouble-free track time.

We reached step four, patted ourselves on the back, and hopped in the car to drive it out of the garage. But then: failure. The car cranked, but there wasn’t even a hint of spark or fire. In layman’s terms, it dun broke. 

We probably should have seen this coming. After all, we hadn’t been able to start the car in a few weeks—ever since it coasted to a stop on a trip from one side of the shop to the other during a spring cleaning. We’d chalked it up to bad luck and went ahead with our safety gear installation. Time would heal that wound, we figured, or at the very least it would be something simple we could diagnose and deal with after the safety gear was finished

Yeah, uh, we were wrong. Fortunately, we’re mechanics—or at least a few of our team members are. No, we’re not talking about experienced weekend warriors, we’re talking about actual, working, professionally trained diagnosticians. So we set them loose on the Fox to chase down the crank-no-start issue. 

The list of problems was long. Remember, our Fox was swapped to a more powerful VW 2.0-liter ABA engine by its previous owners, and the deeper we dug, the more horrors we found. It appeared that the wiring harness, which we’d assumed the team had swiped from the Jetta engine donor, was actually mostly Fox, with a fun smattering of solder/tape/hopes/dreams linking it up to the OBDII engine. Connections were faulty. Wire colors changed multiple times from ECU to engine, occasionally culminating in a color that didn’t appear on any VW wiring diagrams. 

Undeterred, we continued the diagnosis, replacing bad wires, testing components, and continually finding more problems. We found a cheap ECU locally and swapped that in to make sure the computer wasn’t the issue (it wasn’t). We swapped iffy component after iffy component after iffy component. Finally, after creating a car that would make a spark at random but never at the right time, we started down the age-old road of just throwing parts at the problem. Nothing worked, and nothing would make our Fox run. And yes, we tried finding the correct wiring harness for our engine, but months of searching yielded nothing for less than $1000. 

Then, well, we found a bigger problem. Our Fox may have lacked spark, but it now had a blown head gasket. The pressure in the cooling system during our constant cranking confirmed our diagnosis. The culprit? We examined the previous team’s homebrewed heater core delete and realized they’d misinterpreted the factory VW design. What they'd built only circulated coolant through some of the engine. No wonder we’d heard stories of the Fox constantly blowing motors.

Defeated, we stepped back and evaluated our situation:

  • We had a car with a ruined wiring harness. Even if we did get it working, it would always be fragile and difficult to diagnose at the track. 
  • We had a car with a blown head gasket. 
  • We had a car that was swapped with an engine that didn’t really fit, as made clear by the giant hole cut in the hood. 
  • We had a car with the world’s most delicate driveline, one we needed to last as long as possible on track. That driveline was behind an engine that made 60% more horsepower than stock.

After we laid out our situation, the next step became obvious: We needed to press the reset button. That’s how we found ourselves standing next to a rusty 1992 Volkswagen Jetta, safety glasses on, Sawzall and hammer in hand, ready to get to work. 

Wait, what?

You read that correctly. For the princely sum of $500, we bought a running, driving, unmolested 1.8-liter Jetta with a trunk full of spare parts that the previous owner had purchased but never installed. Its only flaw was rust; we made a game of who could fit the biggest limb through the various holes in the car’s floor pan. But rust doesn’t matter on this donor car. 

Our new plan: Swipe the engine and wiring harness, then scrap the rest. Yes, we’d be losing power (the Jetta’s 1.8 is no match for the Fox’s 2.0), but theoretically the new engine would fit under our hood, and its 30-fewer-horsepower output would be less likely to get us 24 Hours of Lemons penalty laps, too. Plus, the entire wiring harness and dash could be transferred to our Fox, making diagnosing problems as simple as pulling up the Jetta wiring diagram. After an evening of work, we’d turned the Jetta into a pile of parts and a $50 check from the scrap yard. Before bed, we installed all of the Jetta’s spare parts, including a new timing set, water pump, tune-up kit, thermostat, coolant sensors and more.

Then, well, we were only halfway there. We spent a few more evenings in the garage, replacing the Fox’s 2.0 with the Jetta’s 1.8. To be completely honest, it was easy. We reused all of our engine mounts, and the only real hiccups involved our oxygen sensor and our oil filter. We fixed the former by drilling a bigger hole in the car’s frame for it to occupy, while we fixed the latter with a generic remote oil filter adapter from Amazon and some love and affection from our plasma cutter. (Sorry, driver-side engine mount!) We reused the Fox’s clutch, radiator, throttle cable, alternator and starter, then moved on to the wiring.


For once, wiring was easy. We mounted the Jetta’s fuse box to the Fox’s dash bar, right next to the passenger door, so it would be easy to access from outside the car. Then we screwed the ECU to the firewall, zip-tied the Jetta gauge cluster in front of the driver, and clipped a few wires we wouldn’t need, like the stereo and power locks. We tied the Jetta’s harness into a stub of the OEM Fox’s rear harness for the fuel pumps and taillights, then turned our attention to the ignition switch. Because this was a race car, we wanted things to be simple and durable. We also needed to install a new kill switch to pass tech, as the Fox’s previous owners had built a multiple-switch system that had 0-gauge unfused positive battery cable running all over the place.

So we called Cartek Motorsport Electronics and ordered some goodies. Instead of a traditional battery kill switch that requires either giant cables running through the car or finicky pull cables, we chose a Cartek Battery Isolator. Why? Because it’s stupid easy to install, replacing the battery’s negative cable attachment to the body and interrupting the circuit there instead of on the positive terminal like most switches. Then, small signal wires run to interior and exterior kill switches and an engine kill relay, meaning no extra positive cables running through the car. Plus, with no moving parts, it should be more reliable than the old-school battery kill switches. 

To replace the Jetta’s ignition, we ordered a Cartek Power Distribution Module and pre-labeled switch panel. These act as fuse and switch in one simple box, and should be easier to use and much more durable than the parts-store switch panel our Fox came with. We used the PDM to power the Jetta harness’s ignition, fuel and starter circuits, then added a new wire to run the electric fan. 

So, here’s where we come clean: We installed nearly $600 of fancy electronics into our $500 race car, but saved hours of work and wired the car almost instantly because of it. Was it absolutely necessary? No, but we wanted to try out some cool new stuff, and the Fox was a great place to do so. We probably won’t splurge like this on our next Lemons car, but we’ll definitely be using more Cartek products on our higher-budget builds. 

While we were wiring the car, we also took a minute to swap our battery, which hadn’t enjoyed its time in storage and was held down by the worst battery tie-down we’ve ever seen pass tech. We chose an Odyssey and its corresponding mount, which saved a little weight and should stand up to the abuse of racing.

We built a downpipe for the car, too, tying the Jetta’s manifold to what was left of the Fox’s exhaust system. An hour’s worth of welding up scraps from the Fox and Jetta and some DEI exhaust wrap should keep us from lighting anything on fire in this department. 

The swap was complete. We pressed “start” and braced for disappointment, only to be surprised by the sound of our Jetta—err, well, Fox—coming to life. The operation had been a success: We’d transplanted the Jetta’s heart into the Fox.

One problem: Longterm medical outcomes are what matters, and we’d only driven our Fox around the yard. Before we could go racing, we needed to check our work with a test day. Wish us luck!

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View comments on the GRM forums
David S. Wallens
David S. Wallens Editorial Director
1/30/20 10:53 a.m.

Small update: The team's currently en route to Barber.

Go, team!

Robbie GRM+ Memberand MegaDork
1/30/20 11:32 a.m.

1st magazine to run the line "project fox: engine swap" that has an article with nothing about mustangs or v8s.

Well done !

David S. Wallens
David S. Wallens Editorial Director
1/30/20 11:39 a.m.

In reply to Robbie :

Thank you, thank you. 

aw614 Reader
1/30/20 11:40 a.m.

I was wondering why you guys bought that mk2 for parts. 

I take the aba can't be used as a spare block to mate with the 1.8 head?

slowbird Dork
1/30/20 11:47 a.m.

I hereby dub thee "Foxjet" as a portmanteau of Fox and Jetta.

noddaz GRM+ Memberand SuperDork
1/30/20 11:47 a.m.

Yes!  Go Team!

Andy Neuman
Andy Neuman SuperDork
1/30/20 2:09 p.m.

Can you send one of those batteries and mounts to Stampie?

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