Engine lean issues

Question

Vehicle is a 2006 Ford Courier, started having hesitation/loss of power after fill up at a gas station that I'd never been to before.

I depend on it for transport so I'm forced to still drive it, which does work, but it refuses to go above ~3000 rpm (even with codes reset, and it doesn't sound like it's hitting a rev limiter or limp mode)

I've replaced the fuel pump and fuel filter, no effect. I did obviously miswire the fuel sender, because the gauge no longer works, but does the PCM use that for anything or is it for display only?

Recurring codes: P0171, P0174

Data log of idle with rev up to 3000:

The data in the graphs is offset a bit because of the slow update rate of my scan tool, but the drop to 0v on both O2 sensors surprises me, any ideas on this?

I've also tried spraying carb cleaner all over the intake/air lines in case of vacuum leak but no surging or noticeable difference that I could hear.

My suspicions at this point are:

• Fuel issue after the pump
• Blocked catalytic converter (exhaust has a strange sound to it sometimes)

Very lost at this point, but I'm trying to stay scientific instead of throwing parts at it. I don't have enough experience to be able to interpret the data from the graphs, but they are clearly indicating an extremely lean condition.

Edit: Data from 30s Idle, 30s 3k RPM, 30s Idle

Edit 2: Log while driving ~50km/h

Answer 1

From the data we have so far (thanks for supplying the second set of traces OP!) I'm leaning towards the Mass Air Flow (MAF) sensor being the culprit.

Looking at the initial traces the air flow figures look way, way too low - unless you're trying this at the top of Mt Everest - and the "spike" from t92 to t94 kind of defies physics, the revs are dropping at this point in time which should lead to a reduction in the airflow. This makes me think the MAF can't be trusted.

If the MAF is essentially under reading most of the time then the other readings start to make sense - if the engine is actually getting more air then it "thinks" then it'll be insufficiently fueling, which means it'll be running lean (hence the flatlined O2 readings during the first run) and it will try and reduce the fueling to compensate, hence the precipitous drops in fuel trim on both banks.

Testing this shouldn't be too hard to do - clear the codes (I'm guessing you'll have the lean codes after running the second trace) and unplug the MAF, it'll probably throw a code for the lack of the MAF and might go into limp mode but it should default to using the MAP sensor and a slightly rich fueling. The O2 sensor traces shouldn't flatline like they have so far, the fuel trims shouldn't have that steep drop and generally be a bit more stable and it won't throw the lean codes.

This was my theory yesterday and I hoped the second trace would confirm this, unfortunately it didn't quite do that, the time lag before the O2 readings flatline after going WOT don't quite fit which is concerning but not enough to make me throw the theory out. Would be good to see airflow readings for that run to see if that clarifies things a bit.

If it's not the MAF my next suggestion would be that there was injector issues, possibly dirt or contamination from the suspect fuel - if that's causing a restricted fuel flow then it would make sense that it was running lean when the revs rise. It fits with the inciting incident being the fill up - but not with the weird airflow readings in the first trace, if the MAF angle doesn't play out I'd be tempted to run some injector cleaner through and repeat the test to see if there's any difference.

Finally I appreciate that you need to be getting from A-B so are having to drive it but I'd be wary of driving it more than you absolutely have to (and gently at that) if it's running as lean as it appears then you're going to be seeing higher than normal exhaust gas temps (EGT) and you run the risk of damaging things like the catalytic converter and the lambda probes.

Answer 2

Sorry for the late update, and thanks for all the help. We finally got the issue fixed: injectors. The old ones had basically no flow at all, except for one, which had way too much flow. I think this weird combination was what contributed to it being so hard to diagnose from the logs. In hindsight the massive boost to fuel was a big sign, but I only interpreted that as too much air rather than not enough fuel... thanks again for your help!