AFR goes crazy.

[JJ Curbelo]

Hi,

I have a situation with my civic FA5 where the AFR goes crazy from time-to-time. This condition, generally appears after a pull. After I finish the pull and start cruising, the AFR start to become VERY rich (11.0:1 or lower).

I've tried:
S. Trims are +-5% before the problem appears
The O2 sensor have 2 years
Tried different MAPs and also tried MAF
Sent the injectors for a service to clean and replace the filters
I've tried a calibration from another FA5 that I tuned

This has happened like 4 times in a 2-year span and normally I need to start from scratch the calibration because even a base map don't work because is "too rich", so I begin to reduce the fuel numbers to a VERY low level until it become lean. From there, I start to increase the values until the ECU asimilates the numbers pero antes de que la ECU comience a comportarte correctamente, tengo que subir sobre 10 calibraciones.



The only thing I can think is the ECU due to the quantity of reflash I've made. I know that the ECU has a very high limit of times that it can be reflash and maybe this is the culprit. Any help?

[Spunkster]

The number of times it has been reflashed should not matter. Are you using live tuning and leaving it on?

[JJ Curbelo]

I'm not 100% sure so, I'll check that and I'll let you know. Thank you!

[JJ Curbelo]

So after a little more than a month, the problem hasn't come! I remember a similar situation I had with the vtec not engaging at the RPM's I tuned, and the issue was an electrical problem with the rear's turn signal. Because I don't like the idea of cutting my OEM harness to add turn signal bulb for my side markers, I placed a connector for this and sometimes, it produced some false contact. I removed all of the remaining connectors and, I hadn't any issue since then. If something changed, I'll let know. I hope this can help our community in any way.

[Lifeisgainz]

Do you have any updates? I have a similar issue with my recently tuned FA5, although mine will run fine for up to an hour after disconnecting battery then it’s back to pig rich a/f. The shop that tuned it has gone thru it a few times now as well as a buddy and I. Everyone is damn near stumped.

[JJ Curbelo]

After a lot of trials and errors, I found that my mistake was trying to set the short trim as close to zero during warm up. The tables that I modified were the cranking fuel tables and the cranking tables that are under coolant temperature compensation. These tables modify the fuel that remains attached to the intake manifold and the fuel that reaches the cylinder. The ECU also takes this amount into consideration and eventually the engine gets lean. I had decreased the values so I increased the values that I had modified again.

Maybe you can start by looking those tables and see if there's any big changes in comparison of your current ones.