I have a 2001 5.4 2v that has 290k miles on it. I've owned it for 5 years and it's been an awesome truck. Recently it has some codes for lean condition on both banks and a non specific random misfire code. P0171, P0174, P0300

It runs rough at idle but only in open loop mode. My scanner shows that the PCM has learned the fix and after the engine warms up it runs fine but it's dumping a ton of fuel to fix the lean code. Also check engine light is not on.

Immediately I assume that the plastic intake is bad, however, I changed this out 5 years ago after buying the truck along with all new plugs, coils, boots etc.

This time I have checked 3 times to find a vacuum leak and can not. My 02 sensors appear to be running fine in the live data. Everything shows to be running correctly in live data except for the timing is jumping for 12° to 25° causing the rpm to jump at idle from 1000 down to 500ish and it has stalled a couple times. Runs absolutely fine at part yhrottle and WOT. I'm probably going to clean the MAF next. Fuel pressure is 45lbs.

Could this be a symptom of the lean codes or possibly a crank sensor? The Camshaft sensor is showing no fault and works correctly but the live data does not show a crankshaft sensor at all.

 

Could very well be a bad MAF. Happened to me. The MAF was producing a bad barometric pressure reading telling the engine I was at 6000 ft elevation. In fact I'm close to sea level. If you are going to replace it, stick with Motorcraft.

 

Well I found the dpfe sensor hoses were bad and went to replace them and the sensor busted when I just looked at it. Lol. I dont think that would cause it but who knows.

I also found my pcv hose had blown off but i dont think that is causing the p0300. I'm going to rescan it after having fixed those issues this morning because it tends to have the rough idle after sitting over night but that is not always the case, it just does it far more often when cold.

 

I had a 94 Ranger that had the DPFE hoses burned off the exhaust pipe end. Turns out it was running on three cylinders (out of four) at that point.

290K miles is a darn good run. I’d do a compression test to make sure that engine isn’t going a similar route.

Also, the PCV hose runs to the back of the intake up against the firewall. The elbow back there rips after some time. It is a huge PITA to deal with.

 

I scanned it again this morning, looking at live data again. The fixes i did yesterday allowed it to run normal enough for ne to check other live data points.

It started running in Open Loop Fault mode. Which I was able to blip the throttle and eventually get it in closed loop mode. This allowed me to see that the front O2 sensors are not performing as well as they should. They are changing but taking a long time to heat up and when they start to work are making changes very slowly but spending a lot of time at low voltage which is indicative of failing sensors.

So my next move is replacing those sensors. that should be the final fix for a while.

The random misfire DTC and the lean codes are now gone.