Before I drove off in his BMW 335d, the owner informed me the JB Diesel Tuner had already been installed and set to max. Good to know, I thought.

He then reached into the glovebox and handed me a box with an OBD2 cable attached with the warning, “You might need this if the car goes into limp mode.” At this point, I have to confess I was a bit disconcerted.

As traffic cleared on the freeway I was able to test this modified 335d. In last month’s issue we have installed Öhlins Road & Track coilovers, 19" VMR wheels with Continetial DW tires plus the Burger Motorsport tune. This was my first chance to try it and the performance was impressive, with the power instantaneous and extremely smooth.

High-speed acceleration was striking. With the automatic transmission into Sport mode at 65mph, I floored it and was sailing past 100mph before I knew it. Cars on the freeway became a blur. Whenever I got a chance to pull away from traffic, I’d open it up but then Bam! – the power cut out and I was coasting. Damnit, limp mode. I guess I had been warned but it was still a surprise, so I limped to the dyno facility.

In the previous issue the owner had noted: “It’s super-responsive and I’m still getting the same 29mpg on my daily commute. The only thing I’ve noticed is if you stomp on it when the engine’s cold, the factory ECU drops into fail-safe mode and the check engine light comes on. But once it’s warmed up, I haven’t had a issue…”

Vehicle Data

2011 BMW 335D Sedan

Engine: 3.0-liter TwinTurbo Power six-cylinder diesel
Transmission: six-speed Steptronic automatic
Drivetrain: rear-wheel drive
Mileage: 18497

Dyno Data

Dyno Type: Clayton VTT eddy current dyno (aka “Mustang”)
Dyno Vehicle Set Weight: 3650 lb
Test gear: third
The baseline and all subsequent testing were performed on the same day, utilizing the same tank of Diesel 2.


Before running the baseline test on the BMW 335d, the ECU was reset with the Bavarian Technic USB OBD2 cable and software to eliminate fault codes and restore stock settings. We did a total of four runs, the peak was as expected (per manufacturer’s claims) but the torque numbers were a bit lower than expected. However, all four runs were consistent with little variation.

Temperature: 75°F
Humidity: 39%
Intake Manifold Temperature: 89.6°F
Peak power: 231rwhp at 4233rpm
Peak torque: 357rwtq at 1989rpm

JBD 60%

Installation of the JB Diesel Tuner (JBD) and adjustment was easy. It took about 15min and we used a 5mm allen wrench, small flat and Phillips screwdriver. By opening the JB control box you turn a dial that allows 0-100% calibration. For our first run we’d set it to 60%.

To make a comparison between baseline and the JBD accurate, the ECU was again reset to eliminate adaptations from the first four runs. To maintain consistency, critical engine temperatures were checked with the Bavarian Technic software to ensure the start and stop engine temps were as close as possible on each run.

All four dyno runs were consistent and again showed little variation in power. However, we were disappointed to see the gains were lower than expected, based on manufacturer’s claims. The gains were consistent with similar devices of this type we’ve tested…

Peak power: 248rwhp at 4095rpm
Peak torque: 373 rwtq at 2050rpm
Max gain stock vs 60%: 18rwhp, 33rwtq

JBD 100%

Parameters for the 100% test were exactly the same as before. We did four runs and, just like the baseline and 60% setting, they were very consistent.

Again, the 100% gains were a little lower than expected but it represents an increase for the 335d with simple installation.

Peak power: 257rwhp at 4012rpm
Peak torque: 377rwtq at 2787rpm
Max gain 60% vs 100%: 16rwhp , 22rwtq


Driving the JBD at 100% was fun. And while I don’t mind throwing a check engine light occasionally, limp mode is another thing and definitely not what you want if trying to overtake, for example.

Checking the ECU with the Bavarian Technic USB OBD2 cable, I found it had thrown six regular and two shadow fault codes. Three piqued my interest because they dealt with fuel pressure and throttle valve capacity, including inconsistent readings from the fuel pressure control system based on long-term monitoring.

So we removed the JBD and reset the ECU to stock settings before the baseline runs. After re-installing the JBD module set to 60%, we saw linear power and torque increases with good drivability and we were unable to trigger limp mode again (and believe me, we tried!)

The JBD allows customers to adjust the power band and the company is upfront about the possibility of limp mode or plausibility code if the product is set to max. With that said, the JB Diesel Tuner is a good upgrade for the 335d engine, and the price is just right. But for added insurance, make sure you get the optional reset tool.


  • JB Diesel Tuner: $279
  • JB Diesel Tuner and CAN ToolL $329


  • Harness uses factory connectors for easy installation and removal
  • Can easily be adjusted to suit power requirements


  • Visual modification easily detectable during service
  • Requires small but reversible modification to the factory connector
  • Increased fuel consumption under heavy throttle
  • Limp mode at 100% under certain driving conditions

Bavarian Autosport
275 Constitution Ave.
NH  03801
Burger Motorsports
2235 First Street
Suite 122
Simi Valley
CA  93065
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