Pegged negative AF Learning - all ranges - no knock - IAM 1.0

As the title says and as shown in the attached screenshot, are these AF results due to a boost leak? Can't be vacuum leak as values are all negative right?

Will do a quick check now. Hopefully, someone will chime in. Car's running fine btw and got 28 mpg last drive. So it's kinna weird .

Found the culprit. Used the technique described on this site to look for leaks and heard hissing around the throttle body.

Took out intercooler and found a loose hose (the big one between the throttle body and the intercooler. Cleaned it up a bit as there was some pretty good amount of oil residue. I think I will need to change the pcv valve.

Tightened everything up. Went for a 190 mile trip WITHOUT resetting the ECU. Pulled LV afterwards. All trims are very good now . However, IAM went down . That may be due to my engine cover not being tightened at all (missing all four screws). I will monitor...

Interesting point. I did not think about that. I did monitor AFR while driving and I thought it looked great.

However, I did notice that when I pushed the car for the first time in fourth gear (after the fix), my max boost went to 18.4 psi. I remember seeing ~17 psi max.

I'd also add that timing has always been around 47deg while cruising compared to 39 on my stage 1 car. I am no tuner, but thought that was a big diff..

right - if it was pulling 15% of fuel with the tb hose leak, then the leak was fixed without resetting the ecu, it would be then running approximately 15% lean, which would cause knock and the IAM drop.

Hopefully it's already resolved

right - if it was pulling 15% of fuel with the tb hose leak, then the leak was fixed without resetting the ecu, it would be then running approximately 15% lean, which would cause knock and the IAM drop.

 

Hopefully it's already resolved

mmh. another good point. Cause I have to say I pushed it in 4th (close to WOT) about 10 minutes after the fix, which was about ~10 miles driving. But then the next 180 miles were just fine and still 27-29 mpg... I should have probably reset the ECU after the fix..

I will post the next LV tonight.

Props to tuning alliance for such a simple way to check for leaks btw. Just need the cap of a spray paint can and good lungs .

I'm guessing your LV will be fine... IAM of 1.000 and nice A/F learning values.

So... 27-29 mpg? I'd like those numbers! Maybe it's the 47 degrees of timing at cruise?

Last weekend I revisited the ignition timing idea. I noticed that my stock 05 LGT ROM had as much as 15 degrees less ignition advance than a stock 09 LGT ROM, and I started to wonder if maybe Subaru learned something in the 4 years after my car rolled off the assembly line...

 

For example, my ROM has 32 degrees at 2000 RPM and 0.5 g/rev, whereas the 09 ROM has 45 degrees.

 

At 1600 RPM and 0.5 g/rev, I have 24 degrees and the 09 ROM has 41.

 

At 2000 RPM and 0.25 g/rev, my stock ROM has 26 degrees, and the 09 ROM has 45 degrees.

 

So, I made a couple of new ROMs, with timing values from the 09 LGT in the 800-2800 RPM and 0.5-1.0 g/rev area. One ROM uses the values from the 09's Cruise timing table, the other uses the values from the 09's Non-Cruise table. The non-cruise table runs the most timing in this area (the comparisons in above this paragraph came from the non-cruise table) and it seems a little smoother. I need to do more A/B testing to be sure though.

 

The result has been significantly smoother driving in the sub-2500 RPM / sub-1.0 g/rev area.

 

I didn't make any AVCS changes because this problem is worst when the engine is cold and AVCS doesn't start operating until the engine warms up. I didn't make any AFR changes because this corner of the fuel table is all 14.7 anyway.

 

I've attached a screenshot of the timing table that I've been running since Saturday, using values from the 09 LGT's non-cruise timing tables. The highlighted cells are the only ones that I have tweaked for this experiment. The corresponding dynamic advance table has no advance in the 0.25 and 0.5 columsn, 1.05 degrees in the 0.75 g/rev column, and 1.4 degrees in the 1.0 g/rev column.

 

I still have more experimenting to do, but I was so impressed by the results of this change that I figure it's worth sharing right away.

^ Food for thought regarding high timing values @ cruise...

Are you using your cars calculated mpg gauge? Mine always reads around 30 but what I do the math at the pump I have never gotten above 25... I think it has to do with tuning and/or larger injectors...

yeah I know that the gauge usually tends to be 'optimistic'. Yesterday 75/25 highway/city was 26.51 mpg calculated (filled up 8.9 gallons and did 236 miles). still not bad .

Mmh, it's now nearly been 100 miles. Just pulled another LV and still .875... I have not been pushing the car for these last 100 miles at full boost to be safe. Fuel trims got worse too. So I just rechecked for leaks and there were none that I could find.

I am now wondering if the tune was really set up with the leak as I can see quite a lot of old oil residue around the throttle body, from where the leak was.

I would contact your tuner and ask him what's up... I would be concerned driving around with IAM <1.00

That's the thing. Trying to get in touch with the previous owner to know who tuned the car. I won't be driving it for the next week btw.

Just to update everyone on this...

Got the car retuned. back to normal now

Great news! Back to enjoying your car

thanks! I love this car. The tune combined with that grimmspeed boost control solenoid, and avo wastegate actuator (and other mods ) makes the throttle response so predictable. Very fun to drive.

Are you back on the road?