Lacking engine performance - 2010 Volvo S40 T5

Hey all, new premium member here! First I want to start by saying thank you to Paul for his wonderful wealth of knowledge. He truly is an amazing teacher, even in online form. Again, thank you, Paul, and please keep up the good work!

A little background on my issue: I have a 2010 Volvo S40 T5; 2.5l 5 cylinder turbo that seems to be down on power. Not substantially, but noticeably lacking. Just for giggles, I plugged in my code reader and saw a pending P0133 code; B1S1 - slow response. It was just pending and I never saw a CEL. The next morning, as I was leaving for work, I plugged my reader in and it was gone (and hasn’t come back since). From a couple videos of Danner’s, he’s said that with this code, 99/100 times it’s just a faulty sensor and to change it. I believe that, but I don’t want to blow $180 on a new sensor. I want to PROVE it’s the sensor. 

Here’s where I’m at.
I’ve been using the Torque Pro app to monitor different PIDs and here’s what I’ve found;

-The car uses a wideband sensor up front. 
-AFR during a WOT run shows a changing signal from ~14:1-15.2:1 and only sometimes showing a 13.5:1 (whereas my Volvo S60 reads 12.5:1 on WOT). 
-Rear o2 is pegged lean at WOT. 
-Fuel pressure at idle is 43.5psi, drops to ~40 on WOT, then slowly climbs after a few seconds. 
-Load PID is showing 100% during WOT like it should.

What I’m finding odd is that the car doesn’t seem to be running off of JUST the fuel map during WOT because with the front o2 unplugged:

-Rear o2 goes full rich (up to 0.8v) during WOT. 
-Car seems to perform noticeably better, but still not 100%. 
-Fuel pressure rises to 50+psi much faster.

Am I missing something? In every video I’ve seen, and from what I’ve found online, the o2s shouldn’t be used during WOT. Why would my rear o2 read lean with the sensor plugged in, then rich with it unplugged? Have I already proved that it’s just a faulty sensor that isn’t performing like it should? Any insight and direction would be appreciated. Thanks!

You have kind of lost me when you state everything you have seen online states the O2's should not be used at wide open throttle. Your wide band sensor at wide open throttle-the air/fuel ratios are telling me you are running lean at wot. forgot to add this - if your fuel system is mechanical returnless your fuel pressure at idle is the same as at wide open throttle.

In every video of Paul’s he states that the o2 sensors are ignored during wide open throttle, meaning the car is solely being run off of the fuel map without the o2 sensors trying to correct. I agree that the wideband is reading lean at WOT, but it doesn’t make sense to me as to why the rear o2 is ALSO lean when S1 is plugged in, but will read RICH when S1 is unplugged.

As for the fuel pressure, both my S40 and S60 have the same return-less system. The S60 will increase fuel pressure as soon as it sees a high load. I’m talking 55+ psi that will settle back down when I come back to normal driving/idle. The S40 should also do the same, but isn’t doing it as quickly. But to add into the mix, all of it seems to be better when the B1S1 is unplugged. 

I’m sorry if any of that is confusing. I’m trying to lay it out as clear as I can. Let me know if I need to clarify anything else!

I misunderstood your statement. Does your upstream sensor give you a voltage and current pid to monitor? Thanks.

I’ll have to dig a little deeper on that when I get home. I believe it’s only the measured AFR pid

The O2 sensors are ignored during open loop. At WOT they should be rich. It sounds like a fuel delivery issue.

I think Torque Pro will generate .CSV data logs? If so, it'd be awesome if you could take a capture of a WOT run so we can look at some data. We're looking for:

RPM
MAF g/s
Absolute Load
Equivalence Ratio
Commanded Equivalence Ratio
Upstream O2 Current and/or Voltage
Downstream O2 Voltage
Loop Status
Short + Long Term Trims

In every video I’ve seen, and from what I’ve found online, the o2s shouldn’t be used during WOT.

For a long time, that was absolutely true! But I've seen many new-er vehicles with upstream AFR's that will remain in closed loop during WOT. Power enrichment is still generated, but is managed by the ECM. It's not universal, but common enough that open loop power enrichment cannot be assumed anymore.

Why would my rear o2 read lean with the sensor plugged in, then rich with it unplugged? Have I already proved that it’s just a faulty sensor that isn’t performing like it should?

You may be onto something. Another WOT run with the above listed PIDs would help clear that up. For example, if your upstream AFR shows a rich equivalence ratio during a WOT run while your downstream shows lean, I'd tend to suspect the upstream AFR. Looking at Absolute Load and the MAF g/s under the same conditions would help to either highlight or eliminate an air measurement issue.

If you do another WOT scan data capture, try to do so from a roll, through first gear and into second, up through third if possible. Highway on-ramps are ideal.

Glad you commented on this Tyler. See my comment on 2006 Ford F150 low power/ lean condition with Paul bill sullivan comment. My thinking only, most wide bands are going to stay in closed loop at wot- and what the downstream sensor is reading - a narrow band sensor- is going to tell us if the upstream wide band is "being truthful".

Just an add on thought on this one- I would definitely do as Tyler suggested on this and I myself would try one more thing. I would add propane with engine running at idle and monitor the upstream and downstream sensors response to the propane enrichment. Thanks

Thank you guys for the responses! I went out last night to do some logging and realized after I got home that it didn’t capture my run with the sensor plugged in. After I’m off work I’ll dial in the PIDs and get them posted ASAP. 

Alright, thanks for your patience. Attached are logs with the B1S1 plugged in and also unplugged. There are 2 different sheets inside the file, so be sure to view both!

Got both captures, thanks so much!

I'm pretty amateur at working with .CSV files, but I managed to get a couple good graphs out of it. From what I can see, it would seem that the ECM is using normal 14.7: AFR through first gear, and only adds power enrichment through second and third gear. That may be why you're sometimes seeing 14.7:1 during wide open. Here's a graph of the plugged in data, with the EQ ratios and the downstream O2:

 

It looks like there's a delayed response, but I think we're actually looking at a slow data capture rate. Partly because Torque is kinda slow, mostly Volvo scan data is slow to begin with. But the ECM does command power enrichment, and it's getting it.

The unplugged data shows mostly the same, just without the upstream AFR:

 

I did note that in the unplugged capture, there's a definite progression in the amount of power enrichment commanded. Not sure if that's a function of the unplugged sensor or not.

Initially, I'm not worried about air measurement or fuel delivery, as it would seem the ECM is capable of achieving the kind of power enrichment it's looking for under load.

What does that mean for your fault code? It's tough to judge sensor reaction times due to the slow data rate. It's been my experience that, while not always stated in service info, the ECM is actually using the downstream O2 sensor to judge the performance of the upstream. Maybe kinda counterintuitive, but many AFR/O2 set ups work this way.

As long as there are no exhaust leaks ahead of the downstream sensor, I'd be tempted to replace both with OE or OEM.

Tyler - I could not even open it lol. Do you think a propane enrichment at idle would give some good additional info on what the upstream and downstream reaction is during actual time of adding propane?

Bills4065, with the front sensor plugged in, I’m actually getting a -10% to -15% on my long term fuel trim. I guess for testing I could add propane but the computer says it’s already running rich at idle.

Thanks for your response, Tyler! Initially I was thinking it was a fuel delivery issue until I watched a video on the premium channel that said to look at the rear o2 at WOT. That’s when I dug a little deeper and saw that it was going lean with the wideband plugged in. It wasn’t until I unplugged it and watched the rear go rich right away that I knew it was likely a faulty upstream. I’m definitely more confident to replace the upstream now than I was a few days ago. Thank you for your insight! I’ll pick up a new sensor as soon as I can and report back!

Could not open your file but thanks for update.it sounds like upstream biased rich-taking all the fuel away.I am with Tyler needs new wideband upstream sensor. No need for propane from what you are saying.