Tuning box problems are usually caused by one of two things
1.MAF sensor signal too high
2.MAP/fuel pressure sensor signal too high
On non adjustable tuning boxes the chances of having either of these two problems is reduced massively but if you have an adjustable tuning box and you increase the settings you are more than likely to run into one of these two problems.
In this article we will focus on the adjustable tuning boxes.
You fit your tuning box, you increase the settings to maximum (because if you can, why not) you go out for a drive and you get a check engine light or perhaps the engine even goes into limp mode.
You get your OBD2 code reader and it says there is a MAF sensor fault.
Why does this happen?
First we need to understand how tuning boxes work.
If you have done any research (by reading the spiel on the tuning box company websites) you will see that one of the main selling features of tuning boxes is how they do not change the engine maps inside the car’s ECU.
If they are not changing anything inside the ECU, how do they make more power?
A simplified example. In the fuel table in the engine’s ECU, we have RPM along the X- axis and fuel pressure along the Y-axis. The tuning box will tell the car’s ECU that the fuel pressure is actually lower than reality and the car’s ECU will compensate by increasing the fuel pressure to the correct level for that RPM, throttle position, air temp, EGT, coolant temp etc etc.
By increasing fuel pressure (on a diesel engine) we increase power.
How is this a problem?
For a set, set of conditions eg 3000rpm, 1400BAR fuel pressure, the car’s ECU has a window in which it expects each sensor signal to be in.
In this example (3000rpm and 1400BAR) the ECU expects the MAF sensor signal to be between 2.5 and 3 volts. It is not an exact number because the ECU has to take into consideration other things that can change eg the outside temperature.
So for 3000rpm and 1400BAR, the MAF signal can be between 2.5 and 3 volts. Between 2.5 and 3 volts the engine’s ECU will be accounting for every possible condition that the original ECU programmers could have imagined ie from arctic temperatures in Norway to heat wave temperatures in Greece.
When a tuning box is making the car’s ECU increase fuel pressure we are pushing to the limits of this MAF sensor signal window.
If the tuning box makes the car’s ECU produce 1500BAR of fuel pressure (when the car’s ECU thinks fuel pressure is actually 1400BAR) the engine will be using/ingesting more fuel, which will increase the MAF sensor signal.
If for example at 1400BAR fuel pressure and 3000RPM and 25 celsius outside temperature, the MAF sensor signal (the measurement of how much air is going into the engine) will read 2.7 volts.
If, under the same conditions the fuel pressure is actually 1500BAR (because the tuning box is tricking the car’s ECU) the MAF sensor signal voltage will be 2.9 volts. The MAF sensor signal is now closer to the limit the ECU will think is acceptable for these circumstances. If the MAF sensor signal goes to 3.1 volts, it will trigger a check engine light (in this hypothetical example).
We get the check engine light because the car’s ECU is seeing that the engine is ingesting more air than it thinks it should be able to given the circumstances. The most common thing a car’s ECU will do when it sees this unusual measurement is say that there might be something wrong with the MAF sensor (it does this by giving a MAF sensor fault code).
This is tuning box “tuning”
Tuning box manufacturers want to increase fuel pressure (on turbo diesel engines) the most they can, without triggering a check engine light.
The same issue can also happen with the MAP sensor and/or the fuel pressure sensor ie the car’s ECU will give a MAP sensor fault or a fuel pressure sensor fault (usually indicated as “fuel leak” on the OBD2 code) if it thinks the readings are implausible for the conditions, external and internal.
In my experience, MAF is by far the most common fault code for the ECU to give when a tuning box has its settings set too high.
Tuning Box Problems – Summary
In a nutshell tuning box problems are caused by either settings being adjusted too high for the engine. In this case, simply reduce the settings on the tuning box and the code will usually disappear.
Or tuning box problems are caused by genuinely faulty sensors or perhaps issues with other parts of the engine eg turbo wastegate.
Generally speaking, I think tuning boxes, especially the more expensive units like DTE and Racechip are used on relatively new cars ie less than 5 years old and cars still under warranty or on lease.
In these cases I think the chances of sensors actually being bad or there being a hardware problem on the engine is low which means 99 times out of a 100, tuning box problems are simply down to the settings being too high on the tuning box.