high miles 2011 xc90 3.2L rich/lean

ikeever · Post by **ikeever** » 13 Jul 2025, 10:56

Friends,

BLUF: This car thinks it's running lean and throwing WAY too much fuel if you leave both O2 sensors plugged in.

I'm reaching out for a little help with Bank 2 lean codes. Long Fuel trims for bank 2 are very high, like +30%. If I leave both O2 sensors plugged in, I get both bank lean codes, and it runs VERY rich, smells like a carbureted 1970 Corvette. Currently, I'm running with only the upstream bank 2 O2 sensor unplugged, and bank 1 is running normal trims, no lean codes, just the bank 2 O2 sensor codes. Open loop on bank 2 with O2 sensor unplugged car runs fine. (3.2L, 275k miles...)

-Smoke tested multiple times, intake and exhaust, no leaks intake or exhaust
-warm/dry Compression test: all cylinders are 190-ish psi +- 3 psi
-Replaced oil trap/pcv, again. (Idle crankcase pressure is -0.06 psi)
-Two new Denso upstream O2 sensors
-6 new plugs/coils
-new Mass air flow
-new bosch fuel pressure sensor (fuel pressure is moving between 55-65psi)
-Fuel pump duty cycle is ~40%
-6 new Denso injectors and orings
-2 new VVT actuators
-Cleaned throttle body

... I'm stumped! Any ideas?

Post by **pgill** » 13 Jul 2025, 18:18

I got a PM with this question and here is my response for everyone to see

You are going after the correct items.

I am surprised with all that you have done that you have such a high fuel trim problem.

Do you have a scan tool that can read mode $06 data?

I recommend that you get one and look into misfiring.

Do you know what a noid light is or have you back probed the injectors to make sure that the electrical connection is good?

If the fuel system is adding fuel then either extra air got in or the fuel is missing.

I would check the actual vacuum in the intake manifold at idle.

The easy way is to use your scan tool and look at the live data.

I did exactly that for my E400 Mercedes and the measurement was BS. It looked good but when I blipped the throttle the reading didn’t change.

If you measure absolute pressure it should go up when you press the gas pedal and the go down very low when you release it and then settle back to where it was where it was before you blipped the throttle.

My Benz did none of that and I had a lot of fuel trim but it was negative not positive.

If the MAP responds as expected then let me know if it is stable at idle.

You can verify with an actual gauge but you will need to remove the fuel vapor recovery valve to find a vacuum line.

Summary of the investigation

1. Check misfire counts

2. Verify electrical connections at fuel injectors

3. Verify MAP sensor is working

4. Confirmed MAP sensor is stable at idle

Report back with your findings

Note: we should post this because Matt is really nice and he asked us to

Post by **scot850** » 13 Jul 2025, 18:24

The other thing that determines how rich the vehicle runs is the temperature sensors. Not sure if the XC90 with the 3.2 is similar to the older 5 cylinder engines in having temp sensor built into the mirror and also on the intake.

Have you confirmed the engine is running at the correct temperature for coolant?

Neil.

Vova585 · Post by **Vova585** » 13 Jul 2025, 21:04

Sorry for your troubles. Never had to deal with such engine so please dont be strict. Issue is localized to bank 2 so I would try to focus here
1.are we 100% sure the upstream O2 sensors are correct for the car and from reputable source? Denso is great manufacturer, but with current cars sometimes it asks for oem part(yes, I know that denso is likely making oem and O.E, but in IMHO it is still different at times). If you are happy with bank 1 fuel trims is it possible to switch(not sure wires length wise) sensors between banks and see if anything changes?
2. Given everything you did above, I think that your next best test is to test backpressure in the bank 2. Possibly catalytic on this side is getting clogged and thats what causes your upstream think that it needs to add fuel.
Best case scenario is to find someone with PiCO scope or alternative and in cylinder transducer. Measuring waveform on the affected bank you will be able to accurately see backpressure presence or no.

You are in Florida, those guys are well equipped
Royalty Auto Service

https://g.co/kgs/7xQRfmi

ikeever · Post by **ikeever** » 15 Jul 2025, 09:15

1. Check misfire counts:

No misfires detected

2. Verify electrical connections at fuel injectors

Fuel injectors are brand new. All connections are good. With a stethoscope you can hear all injectors firing perfectly.

3. Verify MAP sensor is working

Driving 60 mph at 2000 rpm’s the map sensor is approximately 28 inhg. It does fluctuate. Coasting downhill map sensor is 6 inhg with foot off gas. So it appears the map sensor is reading manifold pressure accurately.

4. Confirmed MAP sensor is stable at idle

Map sensor is stable at 7 inhg at idle.

It does appear that the spark advance jumps around more than I think it should between 8 and 12 degrees at idle.
Temperature sensor appears to read normal 90 degrees
Mass airflow while driving at 60 mph is around 28 g/s.
Throttle position does move and correlates with moving the throttle.
Baro reading is 29.8. Local is 29.9
Ambient air temperate says 82 which matches current air temp.
Idle voltage is 14.0 volts.

ikeever · Post by **ikeever** » 21 Jul 2025, 14:11

1. Check misfire counts:

No misfires detected

2. Verify electrical connections at fuel injectors

Fuel injectors are brand new. All connections are good. With a stethoscope you be an hear all injectors firing perfectly.

3. Verify MAP sensor is working

Driving 60 mph at 2000 rpm’s the map sensor is approximately 28 inhg. It does fluctuate. Coasting downhill map sensor is 6 inhg with foot off gas. So it appears the map sensor is reading manifold pressure accurately.

4. Confirmed MAP sensor is stable at idle

Map sensor is stable at 7 inhg at idle.

It does appear that the spark advance jumps around more than I think it should between 5 and 30 degrees.
Temperature sensor appears to read normal 90 degrees
Mass airflow while driving at 60 mph is around 28 g/s.
Throttle position does move and correlates with moving the throttle.
Baro reading is 29.8. Local is 29.9
Ambient air temperate says 82 which matches current air temp.

ikeever · Post by **ikeever** » 21 Jul 2025, 14:13

Can anyone with 100% certainty say the downstream O2 sensors have no effect whatsoever on DME fueling and trims? I’m not an expert on the code. I think they only monitor cat health and nothing more…

Vova585 · Post by **Vova585** » 21 Jul 2025, 20:24

Thats my understanding as well. Should mostly report back to the ecu about catalytic efficiency.

Post by **Krons** » 21 Jul 2025, 20:39

I would give Cataclean a try in case it is the catalytic converter.

ikeever · Post by **ikeever** » 27 Jul 2025, 13:18

Ok might have got somewhere. Investigating knock sensor, I’ve never seen a knock sensor code, but it does ping a bit when cold. But it’s done that since it was new. Anyway, there isn’t any parameter in VIDA to look at knock data, but the parts are cheap enough I’m starting to just throw parts at it. The knock sensor plays a significant roll in setting ignition timing and camshaft timing, which coupled with timing maybe the cause of my lean code????