Parameters after rebuild
02-21-2023, 10:26 PM
#16
Nordschleife Master
02-21-2023, 10:52 PM
#17
Rennlist Member
I was chasing a lean condition after a failed smog test 2 years ago and ended up replacing the o2 sensors and MAF.
As part of my research I came across this info from Callas Rennsport that I saved. https://www.callasrennsport.com/blog/porsche-986-996-987-997-fuel-trim-information
"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."
I don't fully understand the differences on how the .1 and .2 engine management works but these were the numbers after the MAF and o2 sensor replacement.
These are the original pre and post cat o2 sensors.
As part of my research I came across this info from Callas Rennsport that I saved. https://www.callasrennsport.com/blog/porsche-986-996-987-997-fuel-trim-information
"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."
I don't fully understand the differences on how the .1 and .2 engine management works but these were the numbers after the MAF and o2 sensor replacement.
These are the original pre and post cat o2 sensors.
02-21-2023, 11:38 PM
#18
Rennlist Member
I was chasing a lean condition after a failed smog test 2 years ago and ended up replacing the o2 sensors and MAF.
As part of my research I came across this info from Callas Rennsport that I saved. https://www.callasrennsport.com/blog/porsche-986-996-987-997-fuel-trim-information
"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."
I don't fully understand the differences on how the .1 and .2 engine management works but these were the numbers after the MAF and o2 sensor replacement.
These are the original pre and post cat o2 sensors.
As part of my research I came across this info from Callas Rennsport that I saved. https://www.callasrennsport.com/blog/porsche-986-996-987-997-fuel-trim-information
"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."
I don't fully understand the differences on how the .1 and .2 engine management works but these were the numbers after the MAF and o2 sensor replacement.
These are the original pre and post cat o2 sensors.
In this example the TRA is "adding or subtracting" injection time in milliseconds ( ms) to the injection time..example 2.3ms injection time minus TRA -0.02 = 2.28 ms injection time
In this example the FRA is "multiplying " the injection time by the factor of lambda 1 to the injection time...example ; 2.3ms injection time mutiplied by FRA 1.03 = 2.36 ms injection time
This done due to adding or subtracting will give a "finer trim" to the idle range and multiplying by lambda 1 will give "wider/faster trim" to the load range..
Some testers/displays don't use/show "ms or lambda1 " but rather use "%"
Last edited by Porschetech3; 02-21-2023 at 11:56 PM.
02-21-2023, 11:46 PM
#19
This is correct ....
In this example the TRA is "adding or subtracting" injection time in milliseconds ( ms) to the injection time..example 2.3ms injection time minus TRA -0.02 = 2.28 ms injection time
In this example the FRA is "multiplying " the injection time by the factor of lamda 1 to the injection time...example ; 2.3ms injection time mutiplied by FRA 1.03 = 2.36 ms injection time
This done due to adding or subtracting will give a "finer trim" to the idle range and multiplying by lamda 1 will give "wider/faster trim" to the load range..
Some testers/displays don't use/show "ms or lamda1 " but rather use "%"
In this example the TRA is "adding or subtracting" injection time in milliseconds ( ms) to the injection time..example 2.3ms injection time minus TRA -0.02 = 2.28 ms injection time
In this example the FRA is "multiplying " the injection time by the factor of lamda 1 to the injection time...example ; 2.3ms injection time mutiplied by FRA 1.03 = 2.36 ms injection time
This done due to adding or subtracting will give a "finer trim" to the idle range and multiplying by lamda 1 will give "wider/faster trim" to the load range..
Some testers/displays don't use/show "ms or lamda1 " but rather use "%"
Should I be afraid to drive it? I’ve done everything except replace the injectors which I will get to next week.
02-22-2023, 12:13 AM
#20
Rennlist Member
Your display shows % for the FRA 1.14 which is OK
Your display for RKAT doesn't specify " ms or %" , but with an RKAT .05 either way it is very good....
02-22-2023, 08:44 AM
#21
Thanks for your confirmation and insight on this!!
yes, the RKAT is in ms.
im still going to replace/upgrade the injectors to the 996.2 based on your recommendation from another thread.