Help me diagnose this lean running 4.0

Symptoms:

After hard driving (towing 1,500lbs in the mountains, heavy offroad use, stop and go freeway driving), the truck will throw codes for misfire (P0300) and P0171/P0174 (system too lean). The truck will lose power and it can get to the point that it struggles to maintain speeds above 20 MPH. Idle at low RPM can become rough. If I allow the truck to completely cool down (several hours), the truck will return to normal.

Using a Zurich scanner, I determined that the B1S2 oxygen sensor was not reacting to temperature changes in the same manner as other sensors. I replaced it and the sensor now behaves normal. At that same time, I also put sea foam in the engine and a bottle of fuel injector cleaner in the gas tank.

After the sea foam/injector cleaner/new O2 sensor, the next time the truck had these symptoms, they were less severe.

It is very much linked to the engine demand - the truck will not exhibit symptoms unless the engine is placed under demand for at least a 20 minute period of time. Once it starts having the symptoms, it continues until a complete cool down occurs - regardless of decreasing the demand on the engine.

Thoughts?

 

Year and mileage? Any recent work done to the truck? Was it the upstream O2 sensor (engine of the cat) or the downstream? Since you're getting 0171 and 0174, you've got an overall lean condition which makes diagnosis simpler (maybe). Does your scanner show live data? Can you verify that the fuel trims are showing lean?

This could be a lot of things; low fuel pressure, MAF, vacuum leak... I don't like MAF because that should have thrown a code independent of the 71/74 codes. Do you have the ability to test fuel pressure?

 

If you have access to a scan tool.
I’d check the coolant sensor when it acts up.

Besides that, it could MAF Sensor
Fuel pump
PCV
Bad O2 Sensor to ECM communication.

 

2006 and 215k.

It was the downstream sensor on bank one.

 

Original cats? How's the truck for rut. Any change you could have a crack/pinhole in/around one of the cats? That could account for the lean condition, 'thought not on both sides....

 

I did notice that one cat was reading in the 400F temp range and the other was in the 900F range on the scanner.

 

Hello what happened to your truck now? Did you get it fixed? Im having the same problem right now exactly the same losing power then after a minute of engine off it will turn back on like normal but after 20mins its happening again already vchanged the MAF SENSOR sparkplugs same code p0171-p0174 on my 2011 tacoma 4.0 v6

 

I was getting the P0174 and P0171 codes for Bank 1 and 2. Replaced the MAF sensor and codes went away, there was also noticeable increase in throttle response, much better now. I also replaced all 4 O2 sensors, not sure if they needed it but noticed change in idle (got smoother) after replacing the upstream sensors. 162,000 on the odometer.

 

THAT could be an issue...

 

Update:

Ending up being the fuel pump. Replaced and all issues went away.

 

Was about to ask.

Also, check over your vacuum hoses. The ends may be split. Which would also then cause vacuum leaks and poor performance.