Inline tuning can be done the smart way or the cheap way. The cheap way is a fuel-only box that lies about rail pressure and shoves in more fuel with no idea what the engine, turbo, transmission, altitude, or exhaust temperature are doing. That makes heat and soot before it makes usable power. On a modern DPF-equipped diesel, the ECM sees the EGT climb, pulls fuel back, and the tuner’s big promise disappears. In the meantime, you’ve loaded the DPF harder, hurt fuel economy, and added stress where you don’t want it. The fix is not just more fuel. A diesel needs the right air with it, and the added power has to be managed in real time. That’s the point behind the Banks Derringer Tuner. It communicates through OBD-II, watches engine and transmission data live, controls fuel and boost together, backs power down when temperatures rise, trims power during shifts, and compensates when air gets thin at altitude. That’s how you build an inline tuner that adds power without acting like a burn-down box.
Gale Banks begins by separating diesel tuning into two common approaches: flash tuning and inline tuning. Flash tuning rewrites the calibration stored in the engine control module, or ECM, using a handheld device. It is usually the cheaper option because the tool is only needed to upload the tune, after which it can be removed. Banks notes that the quality of a flash tune depends entirely on the person who wrote it. Some are competent and some are not, but all flash tunes leave a detectable footprint in the vehicle's control system, meaning a manufacturer or dealership can identify that the ECM calibration was altered.
Inline tuning works differently. Instead of rewriting the ECM, the tuner is installed in series with one or more sensors. In the example given, the module intercepts the fuel rail pressure sensor signal, modifies it, and sends the altered signal to the ECM. The ECM believes it is receiving normal sensor data and does not know the signal has been manipulated. When the inline tuner is removed, the system returns to stock without the same kind of calibration footprint associated with flash tuning.
Banks explains that diesel tuning fundamentally revolves around two variables: fuel and air. More power requires more fuel, but additional fuel also requires additional air. If the engine does not receive enough air for the added fuel, the air-fuel ratio becomes too rich. That leads to excessive combustion temperatures in the cylinders and very high exhaust gas temperatures, or EGT.
This matters especially on modern diesel vehicles equipped with diesel particulate filters, or DPFs. Banks identifies the affected model ranges as Ford diesel pickups from 2008 and newer, GM trucks from 2007.5 and newer, and Ram trucks from 2007.5 and newer. On these engines, tuning limits are governed by air-fuel ratio and maximum EGT. The ECM controls continuous-power EGT to a nominal 800 degrees Celsius, or 1472 degrees Fahrenheit, to protect the engine, turbocharger, and DPF from premature failure. If a tuner simply adds fuel, drives the mixture rich, and pushes EGT beyond 1472 Fahrenheit, the ECM responds by cutting injected fuel within a few seconds. That reduces temperature and protects the hardware, but it also cancels much of the tuner's added fuel and therefore much of its claimed power.
Banks describes this fuel-only strategy as "stupid rich tuning." It may create a brief surge in power before the ECM intervenes, but it also produces heavy soot, higher NOx emissions, and worse fuel economy. In other words, the engine protection logic prevents catastrophic damage, yet the tuner still creates undesirable operating conditions every time the throttle is applied aggressively.
The core problem is that fuel alone is not a complete tuning strategy on a modern diesel. Without matching airflow, the extra fuel cannot be burned efficiently to make useful power. Instead, a significant portion of it becomes heat and soot. The ECM then has to step in to protect the engine and aftertreatment system. According to Banks, this is why many cheap inline modules promise large gains but fail to deliver sustained performance.
Banks uses the term "burn down boxes" for the simplest and cheapest inline tuners, which only increase fuel flow. These modules are typically connected between the fuel rail pressure sensor and the ECM. By underreporting actual rail pressure, they trick the ECM into commanding more fuel pressure to the injectors, which increases fuel delivery. Banks argues that these devices have no real intelligence because they are not connected to the vehicle data stream and have no feedback loop to understand what the engine is experiencing.
In Banks' testing, these fuel-only boxes fell into two broad categories. The first type adds a large amount of fuel and may claim gains of up to 100 horsepower. In practice, when adjusted for maximum output, these modules often trigger fuel rail pressure diagnostic trouble codes and force the vehicle into reduced engine power mode. They also contribute to DPF plugging, which some users then wrongly blame on DPF technology rather than on the tuner itself. On Banks' 2018 Duramax test vehicle, the best of these aggressive fuel-only boxes added only 34 horsepower.
The second type adds only a small amount of fuel and is commonly marketed as a mileage-improving device. Banks rejects those claims outright. Because the ECM does not know about the extra fuel being added, the fuel economy display on the dashboard becomes inaccurate and may falsely suggest improved mileage. In reality, the richer mixture worsens fuel economy. Banks says many of these boxes appear to share the same internal electronics despite being sold under different housings and brand names. Although some claim gains of up to 90 horsepower, his testing found they all added the same 14 horsepower.
A major part of the discussion focuses on tuner advertising that Banks considers technically impossible. He argues that a device cannot add power without adding fuel, and it cannot add fuel while simultaneously improving fuel economy. He points to several examples of claims he considers contradictory or misleading.
One example is a tuner advertised as not increasing fuel volume while still claiming an additional 70 horsepower and a 10 to 20 percent fuel economy gain. Banks questions how such a result could be possible if no additional fuel is being supplied. He also criticizes claims of no increase in exhaust gas temperature from devices that only add fuel, arguing that higher EGT is an unavoidable consequence of richer operation. Similar skepticism is directed at products claiming gains of 1 to 3 mpg or 2 to 3 mpg while functioning only as fuel adders. His conclusion is that these claims do not hold up once the basic relationship between fuel, air, temperature, and efficiency is understood.
He also adds a regulatory warning: every tuner discussed up to that point is described as not emissions legal, and he notes that both the EPA and CARB are actively scrutinizing such products.
Banks next discusses the AFE Scorcher, which he classifies as an air-and-fuel box, or what he calls a "mouth breather." Although it manipulates both air and fuel, he argues that it still lacks the intelligence needed to tune safely. According to his description, it does not know whether the engine is cold or overheating, does not account for climate or altitude, does not monitor EGT, and has no awareness of drivetrain condition. He also criticizes these types of modules for failing to reduce added power during shifts or torque converter clutch application, unlike the stock vehicle calibration, which can create drivetrain durability concerns.
The claimed output for the Scorcher is 60 horsepower, but Banks says his research showed only a 45-horsepower gain. His broader point is that simply affecting both air and fuel is not enough if the tuner still lacks real-time awareness of engine and transmission conditions.
Banks then turns to the Pulsar, sold by Edge, SCT, and DiabloSport. He describes it as a fuel-only tuner that does have access to vehicle data, making it, in his words, a "smart burn down box." Even with that added awareness, he argues that its strategy is still too aggressive. Around-town throttle application reportedly causes it to inject a large amount of fuel very quickly, which makes the truck feel responsive but harms fuel economy and increases soot loading and EGT.
Banks says the Pulsar also advances throttle response more quickly than stock, effectively acting as a permanent throttle booster. That compounds the problem because there is still no meaningful airflow increase or added boost to support the extra fuel, aside from a small momentary boost rise caused by very hot exhaust energy passing through the turbine. With proper airflow, he says, more of that fuel could be converted into power. Without it, a substantial portion becomes soot until the factory ECM detects excessive EGT and pulls fuel back.
He reports that this behavior leads to much more aggressive DPF soot loading and more frequent regenerations. At elevations of 4,000 to 6,000 feet, the problem becomes worse because ambient air pressure is already lower and the Pulsar provides no altitude compensation. Banks says altitude compensation requires boost control. Based on reports from users operating at those elevations, regenerations were occurring every 125 to 150 miles.
On a 20-second fourth-gear dyno sweep from 1900 to 3200 rpm at full throttle, Banks says the Pulsar added as much as 60 horsepower up to 2500 rpm. After that, EGT exceeded the safe limit and the stock ECM began removing fuel. The gain dropped to 25 horsepower at peak power, then power fell below stock at 3000 rpm. By the 3150 rpm upshift point, output was reportedly 44 horsepower below stock, down to 316 horsepower.
Banks presents the Derringer as the alternative that addresses the shortcomings of the other modules. He says it is the only tuner on the market that controls both fuel and air while making calibration decisions based on feedback from the ECM. The Derringer connects through the onboard diagnostics port and monitors engine and transmission functions in real time.
The tuner's control strategy is described as adaptive and protective. If EGT rises, the Derringer reduces added power to keep temperatures under control. If the transmission is about to shift, it momentarily pulls power back to protect the clutch packs. At higher altitude, where air is thinner, it adds boost to compensate. If the engine is cold, it does not add power until proper operating temperature is reached. Banks' argument is that a modern diesel tuner must manage fuel, airflow, temperature, altitude, and drivetrain events together rather than simply forcing in more fuel.
He states that the Derringer delivers a dyno-proven and road-tested gain of 61 horsepower and 112 pound-feet of torque. He also says it is emissions legal in all 50 states, distinguishing it from the previously discussed products.
To support the performance claim, Banks cites quarter-mile results posted by a customer named Shane from Orlando Speed World. Shane reportedly ran an L5P Duramax equipped with a Banks Derringer and iDash against a friend's truck using a Pulsar. According to Banks, Shane's truck won three runs in a row. The elapsed-time difference was said to be four to eight tenths of a second in the quarter mile, with trap speeds four to six miles per hour faster than the Pulsar-equipped truck. Shane's best recorded speed was 98.81 mph and his best elapsed time was 14.28 seconds.
Banks emphasizes that the Derringer was not designed as a drag-racing product, but rather for street driving and work use. Even so, he uses the dragstrip comparison to illustrate the practical effect of a tuning strategy that manages both fuel and air while respecting engine and transmission limits. His overall conclusion is that safe and effective diesel tuning requires coordinated control, real-time feedback, and protection logic. In his view, any tuner that simply adds fuel without managing airflow, temperature, altitude, and drivetrain events may create a brief sensation of power, but it does so at the expense of durability, emissions performance, and consistent results.