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2014 Ford fusion 2.0l Ecoboost
P0171
This is a speed density system with no mass air flow sensor. My question is based on the behavior of the system when encountering various issues. It is my understanding that I vacuum leak on a speed density system will produce higher RPMs at idle and not a lean code. The map sensors pick up on the extra air and just compensate with fuel which raises the idle. So it would seem on a system like this a lean code would have to be caused by a fuel issue.
To make things just a little bit more complicated the long-term fuel trims drop drastically under engine load. Under enough load the long-term fuel trims can drop to nearly zero. This would suggest it is an air leak issue. But speed density systems should not be affected by it that much. My idle RPMs stay steadily around 760 to 780.
I have used starting fluid, and smoke in the intake and have been unable to find any leak. I did introduce starting fluid into the intake and was able to observe changes in the fuel trim so the O2 is responsive.
The fuel injectors have been sent into me injector for cleaning and testing. Fuel pressure is right where it is desired per the ECU. I've swapped both map sensors and the wideband 02 sensor. Readings before and after we're basically the same.
What am I missing on speed density lean diagnostics?
The map sensors pick up on the extra air and just compensate with fuel which raises the idle. So it would seem on a system like this a lean code would have to be caused by a fuel issue.
Not necessarily, depends how much control the PCM has of idle speed; If desired idle and actual are the same the PCM is happy. As stated that your trims improve upon load you most likely do have an air issue.
Do you have the Freeze frame Data from when the P0171 was set?
Did you block off the purge valve? ( this is common on these units, they stay stuck open)
Is the PCV Valve stuck open or hoses leaking, try blocking or pinching them off.
Is thier excessive vacuum in the crankcase at idle?
im sorry for the late reply. while working to diag my lean condition, i developed a nasty smoking habit that turned out to be a blown turbo dumping oil in the exhaust. New turbo was the solution. So, now that ive got that all sorted i can get back to the lean.
I have looked at the pcv valve. I pulled the separator and made sure it was all clean. The valve flows out but not in so i assume its functioning when i need it to. The hose is solid but I ran the engine with it not connected and the trims stayed high. I have crankcase pressure but from what im told by Ford techs its normal so definitely no vacuum there.
I disconnected the purge valve, where it connects to the intake manifold, after the throttle plate. This is where things got interesting. With that line off, and the vacuum port totally open, my long term fuel trims DROPPED to only 21%. I gave it MORE air, then it ran LESS lean. Im not sure why that makes sense, but i am growing more suspicious of the purge valve. This one, has been on the car for about a year, its a dorman product. Do you have an idea wehre i can go testing from here?
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