Durametric AFR decipher help

[911monty]

Durametric has finally made the cable valuable again. So now that I am able to reliably log data I have taken a snapshot of the AFR loop minus the MAF. Looking at this graph it appears to me that my car is running healthy, with no apparent vac leaks. Is there any data that needs to be run with this to make a proper evaluation? Any thoughts and input are appreciated since I would like to learn what I can. Thanks



Additional test data was 800 rpm and MAF was 12.25kg/h. My basic interpretation is there might be some improvement if I replace the MAF?

[jcslocum]

That looks very good! Is that FRA and FRA2?? Mine does not read like that!

[911monty]

Originally Posted by jcslocum

That looks very good! Is that FRA and FRA2?? Mine does not read like that!

Yes! That's what I think I'm seeing also. I think FRA & FRA2 are supposed to be 1 and are both 0.97, TRA and TRA2 which I think is STFT? are both pretty much zero,. The only one that appears to be slightly questionable is O2 ahead of cat bank 2 which should be 0.5. and is 0.73. What I think I'm seeing is that these are pretty much what they are supposed to be, however It appears the MAF is introducing some fluctuation and possibly needs replacing?

One thing I need to verify is what is STFT and LTFT? The durametric does not define fuel trim that way.

[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.

[jcslocum]

MAF is quite dependent on RPM and that i didn't record. I can do this over next weekend, when I return home. It's interesting to see yours so low.

Can you log your RKAT for me? This is the trim at idle. FRA is trim at running engine speeds not idle. I have no idea what this should read but I think my numbers are very high but not out of scale.

[911monty]

Okay Give me a few. RKAT is adaptation range according to your pic, anything else you want to see?

[911monty]

Well maybe I need help finding it......below is a pic of my available options. It doesn't indicate that it is available? The number 5 and 6 windows are TRA and TRA2 on my original chart. My DME is a 5.2.2. I see yours is a ME 7.2?

[flaps10]

Great thread for those of us just learning how we can use Durametric properly.

[911monty]

Whew! After much searching I have found the following definitions for the Durametric TRA and FRA values for the DME 5.2.2. Apparently the later DME versions break down the values into RKAT etc.





The following are the set points for the DME 5.2.2 from the OBD manual that is no longer available available for purchase.




Hopefully this thread can gather some of the Durametric info spread around the various forums etc. where it can be a little easier accessed. So if you have info please don't hesitate to contribute. I know there are some sages out there. TIA.

[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

[smshirk]

This is great stuff. I would love to see more. Ive had durameteic for several years, but am not well schooled in its use. I have 2 cars with ME 7.2, plus a 968 that Is pre obd2. I'm not sure the tool is a lot more helpful than a generic code reader for that car, but I hope I am wrong. Of the 3 cars, the 968 is by far the one with the most issues. It gets terrible gas mileage now, a dramatic change that has occurred over time. It seems to run fine.


Sent from my iPhone using Tapatalk

[jcslocum]

OBD1 will not work that I'm aware of.

I can post some infor tomorrow night as I will be at the shop and will be changing out my MAF so I can take some before and after readings.

[911monty]

Originally Posted by jcslocum

OBD1 will not work that I'm aware of.

I can post some infor tomorrow night as I will be at the shop and will be changing out my MAF so I can take some before and after readings.

Looking forward to new data. Curious though as to why you're changing MAF, yours looks to me to be okay, but as you pointed out your positive adaptation values seemed to indicate a leak. Did you get that resolved?
Helpful hint: In case anyone else has noticed the scales on the graphs in my previous posts are sometimes not appropriate for the parameter that is being measured. Unfortunately the Durametric software attempts to pick the appropriate scale but it cannot be changed by the user. The solution is to export the log to excel where the data can be seen in detail.

[jcslocum]

I think I have the later MAF in an older Box so I have found an older new unit to try and see if that fixes some of my readings. I did some data logging today but the screen grabs didn't work so I can't share that today. I have the excel log file and will work on charting it.

At idle my MAF reads right at about 15 kg/h. Once the A/C is switched on the MAF reading goes to about 18.5-19 kg/h. The idle RPM does stay essentially the same, right about 825 RPM. The car goes in for a safety inspection tomorrow morning so it can be registered here in MD from VA. Once that get done, I will put the new MAF in and take it for a spin and record the same stuff again.

I'm chasing a hard start when HOT situation. We think we have a vacuum leak that is making idle too lean which is shown by the readings. More work and more data to come.

Some really good logging info I have found:

http://www.6speedonline.com/forums/996-turbo-gt2/320625-durametric-logging-101-how-log-what-log-what-do-afterwards.html

[911monty]

Yep that's a good read. Don't know if you saw this one but I really like it. The youtube videos are great and he really does a great job of explaining how to determine leaks.

How to diagnose and resolve engine issues using Durametric.