PCV Valve?

[Rearanger]

I'm thinking the PCV system needs to be balanced with computer controlled fuel trims. The fresh air replacement air is taken out of the metered air stream, if that is not replaced equally through the PCV then the fuel trim would be off.

I think my PCV system is operating properly with neutral pressure/vacuum.

Closed PCV system is for pollution control, as you know.

 

[RonD]

Any PCV(positive crankcase ventilation) system is to prevent air pollution.

Closed is just better at it than open.

PCV Valve air is allowed for in the base 14:1 fuel calculations, yes, based on engine RPMs and throttle position, its air volume is added to MAF data air volume.

Fuel trims are done from O2 sensor data.
And with a MAF system even with a vacuum leak engine doesn't run Lean, or with a leaky injector it doesn't run rich.
Unless there is an extreme leak for either, lol.

The CEL coming on and a Lean or a Rich code means the computer is still running the engine according to O2 sensor feedback, but the fuel trims are either too high or too low based on MAF sensor data and the base 14:1 air:fuel calculations the computer is doing on the fly.
On the fly the 14:1 fuel trim is 0, -1 trim mean computer is adding less fuel than calculated because O2 sensor shows a little less oxygen in the exhaust, +1 trim means computer is adding more fuel because O2 is showing more oxygen in exhaust.
It is different on many systems but -10 to +10 is normal range for fuel trims.
-20 and +20 fuel trims are when computer will turn on the CEL to notify driver there is a problem, a code like P0171 means lean on bank 1, but engine is not actually running lean, computer is adding the extra fuel to keep the oxygen level in the exhaust where O2 data says it should be, the code means the base 0 fuel trim calculation is wrong, computer is having to add too much fuel to the air volume the MAF sensor says is there.
A leak in the PCV Valve hose can cause this code, but a vacuum leak is not the only reason for this code.
Low fuel pressure means the computer has to open the fuel injectors longer than it should need to, so +20 fuel trim
-1 means injector is open less time, +1 means it is open a longer time, injector pulse width or dwell time, is the fuel trim.

O2 sensor data along with computer keeps exhaust oxygen levels where they should be, regardless of vacuum leaks, low fuel pressure or PCV Valve failure, but only as long as O2 sensor is working right, lol.

 

[JP02XLT]

I get the p0171 & the p0174 codes randomly, my LTFT's are generally in the -3 to +5 range, the short term FT's are in the -2 to +2 range, I have replaced the stock PCV system with a catch can setup that also utilizes a one way vale on one valve cover to let air into the system and the pcv valve into the other that keeps a constant air movement to vent the engine, I do not put the exhausted PCV air into the intake tube as Ford did, it is routed to the catch can & then back into the other valve cover to create the loop. I did this because of the supecharger, at times with the typical pcv system it would blow oil vapor into the intake tube. This way I blow the vapor back into the valve cover, but venting the block this way is a true controlled vacuum leak by the inlet check valve in the valve cover.

Even before changing the PCV system I randomly had the P0171 & P0174 codes, I have checked all the hoses, connections etc & I still get the codes once in awhile.

I also wanted to add that the truck has a wide band O2 setup on it and under "normal" driving it stays any where from 14.6 to 15.0.

I dont think the Ranger ECU corrects the trim levels as fast as some other vehicles, Dad has a 2010 Jaguar that keeps the short term trims at or near 0 consistently, my truck wont do that.

JP02XLT