Porsche 986-996-987-997 Fuel Trim InformationPosted on: 23, June, 2013
Hey Tony, Can you shed some light on a fuel trim fault on my 996. It is reoccurring and I am having a tough time finding the problem.
Anytime you have a ME 5.2.2 (1997-1999 986-996), ME 7.2 (E-Gas 986-996) or 7.8 (Roughly 2002-on) 986 and 996 with running issues, check the fuel trim numbers: TRA-RKAT (Idle range which is around 1700 and below) FRA-FRAU-FRAO (cruise range which is around 1700 and above) fuel trim numbers.
The Oxygen sensing AKA Lambda or on the later models they call it “fuel trim mean value” is “STFT” short term fuel trim. The TRA or RKAT and FRA or FRAU-FRAO are the “LTFT” long term fuel trim. For TRA and RKAT you want around them “0”. If it is below “0”, the car is running rich at idle and it is taking away fuel in the Idle range. If it is above “0” the car is running lean and it is adding fuel at the idle range. The FRA or FRAU-FRAO should be around “1”.
If it is below, the car is running rich in the cruise range and it is taking away fuel. If it is above “1”, the car is running lean in cruise range and it is adding fuel. NOW, most of the time, when the car has a faulty MAF,it will affect the TRA-RKAT or idle range.
The TRA-RKAT numbers will be LOW or BELOW 0 and the FRA or FRAU numbers may be normal around 1. ALSO, check the MAF numbers with the car at idle. The MAF numbers on a Boxster should be around 15 kg/h. The MAF numbers on a 996 should be around 17 kg/h. The MAF numbers are usually +/- 2 depending on the EVAP situation.