Durametric AFR decipher help

[jcslocum]

STFT = Short Term Fuel Trim

LTFT = Long '' '' '' ''

These are my latest readings from a few weeks back. I'm chasing some vacuum leaks as you can see.



Mine are high at idle showing that I'm running lean at idle.


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.

[911monty]

Thanks Jcslocum for that. I knew what STFT and LTFT stood for, but didn't know what the Durametric value was for them. Your explanation and pic with the adaptation trends helped a lot.
As you can see by my lower pic my MAF is only reading 12.25 at idle instead of the 15 +/- 1.25 that it should be. This would indicate a leak, but with fuel trims as they are I think a new MAF may be in order? As added detail there are no codes reported.

[911monty]

Originally Posted by jcslocum

STFT = Short Term Fuel Trim

LTFT = Long '' '' '' ''

These are my latest readings from a few weeks back. I'm chasing some vacuum leaks as you can see.



Mine are high at idle showing that I'm running lean at idle.


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.

The following verifies jslocums definition and shows the detail in the later DMEs. So us with the DME 5.2.2 will have to make do with TRA and FRA........

[911monty]

Armed with the above information it appears on my first graph that the TRA2 is a bit rich at idle and the injector pulse width is being shortened as indicated by the -0.03. This is also supported by the yellow trace in the second graph showing the MAF value with the swinging 02. i do have a rich exhaust smell at idle. My next steps will be to run the set points and see how mine stack up, I will also run the test at 3000 rpm to see the change to the FRA/FRA2 trends. Possibly tomorrow since it is already 96 deg outside and ash is everywhere. I still suspect the MAF but will continue to attempt to verify. Thoughts?

[911monty]

Was able to log some more data.

DME 5.2.2 set points



My engine logs



and the rest




Everything again appears to be normal except spec air mass and spec air adaptation. The other anomaly is the exhaust temp is low, is this excessive EGR or crappy California fuel. Hmm.

Lastly we have the FRA at 3000 rpm. Appears to be normal again. I'm pretty sure at this point a new MAF is in order but would welcome opinions. Thanks