For this gentleman, it cost him a new motor!  For those with the 2008+ STi and 08-14WRX, your fuel pressure based power losses could be adding up.  To eliminate any losses due to dropping fuel pressure look into COBB’s fuel pressure differential kit.  We have highlighted a recent re-tune we did to help show the amount of power lost due to low fuel pressure.  This can be seen as poor atomization and most commonly inappropriate scaling due to missed pressure drop.  This unfortunately cost this owner a new motor.  Had fuel pressure been monitored and scaled for, there would have been no catastrophic failure.  Onto the original question, how much power is it costing you?  Well in this example it was:

50+ HP!

Green is our tune

Red is previous competitors Pro-Tune

Where did things go wrong on the previous tune, and how far off were things?  Well lets start with constants:

  • Boost 24PSI on previous tune
  • Boost 23PSI on ours
  • Timing optimization on our tune lead to power gains onto boost
  • Fuel pressure optimization lead to power gains on boost
  • Previous tune ran 13.1-13.5 AFR on boost!!!
  • Both were done on a built EJ257
  • Both tunes were set for E70 (ours was flex-fuel)
  • Both were accessport based Pro-tunes
  • Both were done on MD-AWD500 Dyno’s
  • Ours took 1/2 the time to complete

So, where did the previous tuner go wrong?  Well, the didn’t account for dropping fuel pressure on a very high demand fuel system.  The fuel injectors could more than cope with any and all the fueling demand, however the fuel pump was not up to par.  Since fuel pressure was dropping, they decided to increase MAFv scaling to compensate for the change in fuel pressure.  With our tune, the MAFv scaling stayed the same, we used the fuel pressure differential to compensate the injector opening.  We ran less timing at peak torque, as the previous tune was past MBT.  The reason our tune made less power at peak torque was due to the lack of over-fueling.  We also elected to drop boost by 1 psi, to help mitigate heat soak of the intercooler.

Example of fuel pressure compensation in action

Example of fuel pressure compensation in action

Missing critical elements in a tune wastes the customers time, and money.  By missing the fuel pressure drop, not only did they waste time and money; but a perfectly good built motor.  A fuel pressure sensor could save your motor.  If you have the option to install and run one, we highly recommend one!  Follow the link on the picture to purchase a COBB Fuel Pressure Sensor for your vehicle.  The 225 price tag will seem trivial compared to a new motor!

Click the sensor to be taken to the product page

The 50 hp comes from : 39*1.28(powertrainloss)=49.92.  This was the peak difference between the two tunes.