Running rich - jumps in Fuel Trims

Hi all,

Fixing up an 2002 Impreza TS (though I'm sure you'll forgive me) that I picked up cheap with mis-fires and rich codes. So far done timing belt, plugs, filters, patched up exhaust....

Basic problem is that it has 'moments' under light load where the response dies/it slumps heavily. Clutch in and accel kick seems to re-waken, but I'd like to understand the problem and fix.

Initially I though it might be fuel regulator, but that seems fine (at least at idle/static).

Off prime = 34psi

Idle = 36psi

Idle (vac disconnected) = 44psi

Deadhead/return blocked = 76psi

Off @ 2:05pm = 40psi

Off @ 2:15pm = 40psi (so no leaks)

I believe that I caught on the these 'events' in line 764 (32910ms) in the attached log. The output does not seem to make sense! All of a sudden the combined fuel trims jump from -10% to +10%, injectors open up and the AFR drops....

Anyone here have a suggestion what else I can log, or check out? Is the ECU seeing another sensor issue, and making a bad decision?

Cheers, Simon

romraiderlog_20170827_imprezza_20170827_150702.csv

Nice fix-up target! See if you can log CL/OL Status, A/F Learn and Correct #3 (especially if the car also has a rear O2 Sensor.

Not sure if those cars, ECUs had a concept of a 'Learned Value' (LV). If so, see if you can capture an LV to see what Fuel Lean ranges, IAM and Learned Timing look like.

Did some more logging, with the added parameters you suggested. Couldn't find the CL/OL flag though :-(.

In the attached log, starting around line 6900 (496859ms) I got a big 'slump' pulling away from waiting at traffic lights.

I note that the rear O2 sensor does not seem to be doing much. Can anyone confirm whether this influences fueling, or whether it is only used for emissions monitoring. Part store lists this as different from front O2, is the active part the same (I have an old front I could patch in... maybe)?

One thing worth stating is that since it was brought at auction I have zero history on this vehicle, so I don't really know what might have been 'fixed' previously or could have been swapped out for incorrect parts (injectors?). When I got it, it was missing the inlet ducting so presumably previous own used some form of pod filter.

The ECU-ID (0x1B12000405) is not recognised RomRaider, so 'Learning View' is not possible, and does not produce any hits in Google.

I'd like to understand issue, rather than just drop in new parts on a hope and a prayer... but the local breakers yard is having a sale this weekend.

Simon.

PS. Again the car is the 2002 Impreza TS 5-sp, 2.5L with MAP (and no MAF).

romraiderlog_impreza_rich_20170828_184631.csv

For the section which is 'bad' (from line 6900); I note that the 'Learned Ignition Timing (degrees)' is asserted (values above 4) for a much longer duration - whist the combine Fuel trims are around -35 to -40%. It seems to stay this way until I let up on the accelerator... around 8s.

This seems 'better' at other points in the log, when I was pulling away from a standstill. Wonder whether this is a cause or a symptom?

Simon

Forgot to stress that this car is not throwing codes, just that the trims seem a little excessive and it has the driving issue(s).

Injectors confirmed as "FBLC100 000 1727", although not convinced that these are correct, seems that the Impreza/Forester have different to Outback/Legacy:

http://www.autozone.com/fuel-delivery/fuel-injector/gp-sorensen-fuel-injector/56619_594834_0

http://www.autozone.com/fuel-delivery/fuel-injector/gp-sorensen-fuel-injector/262621_594834_0

ECU is also confirmed "22611 AF402", but don't know that the tune is stock.

The other thought I had was perhaps the Air Assist Solenoid is the reason for bogging sometimes from idle. It appears that this introduces air from in-front of the throttle plate, and thus would not be accounted for by the MAP sensor.

http://www.scoobyluke.co.uk/scoob/techdoc/engine/fuel.pdf

The valve is located in the piping between the throttle body and the air assisted injectors and is secured to the intake manifold. The valve is connected to the inlet side of the idle air control valve to regulate the flow of air to the base of the air assisted fuel injectors. At idle, the air assist solenoid is ON, allowing an airflow of 20 liter/min per injector. The air assist solenoid is turned OFF during off idle conditions, allowing an airflow of only 5 liter/min per injector.

I experimented a little with it, seems that it is not closing off completely. Maybe it's sticking in real driving. Completely open/closed did not have a huge effect on the trims at idle/static.

Perhaps I am just overthinking this problem and its just the O2 sensor lying. It does seem to be 'working' with changing values, but maybe it's worn out in some way.

Simon

Update:

Although didn't have data to confirm that the O2 sensor was lying, I (finally) swapped it out and the fuel trims (and driving behavior) improved substantially.

Simon.

Final solved.... although not having any evidence (that I swore I'd get before throwing parts at it) I swapped out the O2 sensor and all is fine.

Dam you you lying O2!!!

Simon.

PS. Now have transmission issue to deal with :-(