How To Hack Your AFC on a SRT4

Project SRT-4 has had a colorful life so far but there’s no denying the impressive beastly nature of the 2.4 liter A853 turbocharged engine. Large frame turbos put this engine right in it’s wheelhouse with good displacement and lots of torque. It’s a lot of brute force front wheel drive fun and without a doubt quick for a four cylinder sedan.

Our article will help those who don’t yet know how to hack your AFC on a SRT4 for maximum tuning range and ability. This modification can truly justify the use of an Apexi Super AFC NEO in your Dodge SRT-4.

Various forms of ignition timing have been tried on our Project SRT4, but our personal favorite is the Stage 3 Toys unit that provides 3 additional degrees of ignition timing at WOT. Success with the Super AFC NEO is unquestioned but we’ve still had our share of tuning closed loop control issues. Our How to Install page is a good place to start, but many SRT-4 owners do not want the AFC because of the voltage issues.

The throttle range on the A853 engine is 3-7 volts, therefore making tuning of the AFC NEO difficult to say the least. Instead most people use the MAP sensor as the TPS, as we do in our How To Install SRT-4 AFC NEO article. 

In theory this hack to your AFC NEO will get the job done at wide open throttle (WOT) or on the dyno. You are tuning “ranges” of positive pressure, or voltage based on pressure above atmosphere. It’s simple, direct and works very easily with the ability of the Super AFC. Instead of tuning engine speed ranges and locking into air fuel values, you are referencing boost and your tuning curve is very evident and uniform.

However the problem arises when you must tune closed loop control and cannot get the granularity or control you need. Because the pressure is a reference instead of true throttle control, the issue becomes quickly apparent when driving around town.

Driving up a hill or putting different ranges of load on the engine are difficult to tune and cannot be achieved because the turbo will spool differently in those ranges. Lean spots and excessively rich spots can cause long term issues if you are not constantly tuning the AFC NEO.

There’s no questioning the piggyback unit’s abilities at WOT, Project SRT-4 has put down 389 to the front wheels and 390 in torque using the tubular DNP manifold and a large frame 62-1 Turbonetics turbocharger. With an additional MSD 3 bar map sensor you can achieve the exact range you need at WOT, which makes the AFC NEO piggyback device perfect.

Our How To Hack Your AFC on a SRT4 article will give you the ability to adjust your throttle in a completely separate way. Translating your TPS sensor directly to the Super AFC, you can now truly use the piggyback fuel computer as it was originally intended.

No longer will you be restricted by boost specific tuning intervals without the added dimension of throttle, part throttle is freed up for you to tune. Gas mileage itself is a perfect reason to learn how to hack your AFC on a SRT4.

Our how to hack your AFC on a SRT4 fix is a series of voltage rectifiers soldered into each other to lower the range of the A853 throttle position sensor voltage to the acceptable 0-5 volt range. 

These rectifiers are very small and cheap and you can run up to three inline and in series before the signal becomes a bit too faint. Every resistor steps down the voltage as well as the signal, so don’t go too wild.

Instead of teeing into the MAP signal as the throttle reference on your Apex Super AFC NEO, you can now truly use throttle. Solder the resistors inline and tee into the throttle position signal wire, giving the AFC the range it needs.

Using this method we are able to put up real world figures and gains in gas mileage. Over 16 mpg in gas mileage and a much more consistent dyno run that we will shortly post. Using a voltmeter you can simply test your range output by turning the vehicle to the “ON” position and depressing the SRT-4 throttle down all the way. Voltage on our setup nets a 0 – 4.65 voltage range.

Make sure to check out our knock sensor DIY for the SRT-4, and please let us know if you have any questions or comments about our How To Hack Your AFC on a SRT4 guide.