[Boxer-Moto]

1999 9-3 HOT. Generic Bluetooth OBD2 module with the Torque Pro app...

Short term fuel trims are pretty low and behaving like I would expect (low single digits and fluctuating). However, the readings I'm getting for long term fuel trim are 35%...

I have a vague recollection that there is a quirk that makes the Tech2 the only reliable measure of LTFT. Something about the ECU reporting it incorrectly to aftermarket devices.

Anybody know anything about this? Am I crazy? Google and the site's search feature haven't turned up much.

I'm pretty confident I don't have vacuum leaks (I've replaced them all and I have smoke tested the car). I do have a probable leak at my exhaust manifold (two broken studs...will be fixed this weekend) and my O2 sensors are who knows how old. BUT...how can my LTFT be so high when the STFT is normal? If long-term is essentially an average of the short-term, shouldn't it be a lot lower?

I should probably just drive and forget about fancy apps.

 

[jvanabra]

Trims are related, but ST is "now" and LT is "over time" so it's possible to see values very different from one another depending on the sampling interval. ST may only read X, but it may be reporting other values at intervals where there is no query. Broadly speaking, LT is the valuable one.

I dont know about T5 misreporting values... I'm not sure how that would work since OBDII datastreams are very well defined. Not saying it isn't possible, but I have never heard of such a thing.

Are you seeing positive 35% or negative? A high positive is definitely possible if you have leaks in the exhaust.

 

[Boxer-Moto]

Okay. I guess I need to do my head swap, clean up the known potential leaks, and re-evaluate. I will report back next week.

 

[jakejm79]

I think, IIRC, that the issue with the LTFT and T5 was that the system was calibrated to report 25% has a 100%, i.e. this results in the values being 4x higher than what they actually are, so your 35% would really be around 9% - which is in the range of normal.

Now I don't know if any of that is true, I just remember that was the discussion.

 

[jvanabra]

I think, IIRC, that the issue with the LTFT and T5 was that the system was calibrated to report 25% has a 100%, i.e. this results in the values being 4x higher than what they actually are, so your 35% would really be around 9% - which is in the range of normal.

Now I don't know if any of that is true, I just remember that was the discussion.

This is reported on trionictunung, so it very well could be. Interesting!

 

[Boxer-Moto]

I just found the info in WIS...

It's in Trionic T5 OBDII ---> fuel injection ---> Global Adaption

The system is capable of +/- 25%...which Tech2 reports as 100%

...so, my ~30-35% should be around 8-9%. I will see how/if that changes when I fix the exhaust manifold leaks.