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Bank 1 system to lean 2001 ford ranger


DZita88

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My 01 ford ranger 2.3 5 speed has been getting engine code p0171 for about 4000 miles now. Bank 1 system to lean. I replaced the intake manifold about 15000 miles ago. I took the intake manifold off to reinsure everything was sealed well. I replaced my pcv valve and my fuel filter recently. I propane tested all of my vacuum lines to check for leaks. Everything is sealed well. I took it to the ford dealership after taking the manifold off to have them check the code. They found a vacuum leak that was just a hose disconnected. They re attached it and my light still came back. I figure the vacuum line they found disconnected was probably one I forgot to hook up when I put the manifold back on. My mechanic found engine code p1537 IMRC stuck open. Ford tested the IMRC and said it is functioning properly. I frequently get it scanned and cleared and keep getting p0171 bank 1 system to lean. I have tried everything I could think of and already spent 600$ to mechanic/ford to get rid of it with no luck. Anyone had a similiar problem or have suggestions??? Or know of a good place near the SF Bay Area?
 


RonD

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A DTC code means computer has reached a parameter set in the software

P0171 means the computer is opening fuel injectors at a dwell time that is at or above it's factory dwell parameter.
Dwell for injectors is also called Pulse Width.

O2 sensor reports Oxygen content, not fuel content.
You just have the 1 O2 sensor for lean/rich on a 4 cylinder engine.
Bank 1 sensor 1

Bank 1 sensor 2 is after the Cat it tests if Cat is working and is not used directly for fuel trim.

So P0171 means there is more oxygen in the exhaust as reported by O2 sensor, than there should be, not less fuel than there should be.

A leak in the exhaust manifold will suck in air, giving a false lean to O2.
When a cylinder misfires none of the oxygen in that cylinder is used/burned, O2 sees that as lean, too much oxygen.

You have looked at extra air coming in from intake which of course would through off the computer calculations.
Computer bases center parameter of air/fuel mix on the MAF(mass air flow) sensor data.
MAF data sets the 0 for the RPMs and load.
Computer then trims the dwell time of injectors with -1(opened shorter) and +1(opened longer).
It then watches the O2 sensors voltage to see which way to trim, normally the trim will constantly change between -5 and +5, this is the computer trying to stay as close to 0 as possible.
If computer gets to +20 for any length of time it will set P0171

This is based on MAF sensor correctly setting 0, which doesn't happen with air leak(vacuum leak)
O2 sensor correctly IDing oxygen levels, which doesn't happen with exhaust leak or older O2 sensor
All cylinders firing
Computer working correctly.

And Fuel Pressure at 65psi(2001 Ranger designated pressure), lower fuel pressure requires increased dwell time.
 
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dla

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A DTC code means computer has reached a parameter set in the software

P0171 means the computer is opening fuel injectors at a dwell time that is at or above it's factory dwell parameter.
Dwell for injectors is also called Pulse Width.

O2 sensor reports Oxygen content, not fuel content.
You just have the 1 O2 sensor for lean/rich on a 4 cylinder engine.
Bank 1 sensor 1

Bank 1 sensor 2 is after the Cat it tests if Cat is working and is not used directly for fuel trim.

So P0171 means there is more oxygen in the exhaust as reported by O2 sensor, than there should be, not less fuel than there should be.

A leak in the exhaust manifold will suck in air, giving a false lean to O2.
When a cylinder misfires none of the oxygen in that cylinder is used/burned, O2 sees that as lean, too much oxygen.

You have looked at extra air coming in from intake which of course would through off the computer calculations.
Computer bases center parameter of air/fuel mix on the MAF(mass air flow) sensor data.
MAF data sets the 0 for the RPMs and load.
Computer then trims the dwell time of injectors with -1(opened shorter) and +1(opened longer).
It then watches the O2 sensors voltage to see which way to trim, normally the trim will constantly change between -5 and +5, this is the computer trying to stay as close to 0 as possible.
If computer gets to +20 for any length of time it will set P0171

This is based on MAF sensor correctly setting 0, which doesn't happen with air leak(vacuum leak)
O2 sensor correctly IDing oxygen levels, which doesn't happen with exhaust leak or older O2 sensor
All cylinders firing
Computer working correctly.

And Fuel Pressure at 65psi(2001 Ranger designated pressure), lower fuel pressure requires increased dwell time.
Excellent description - thanks for taking the time to type all that out. I learned something on this board by reading it.
 

DZita88

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Wow thank you so much for the long detailed reply. I truly appriciate that. So essentially you think it is an exhaust leak somewhere between the exhaust manifold and 02 sensor? It would make sense why is still runs great if it just had a minor exhaust leak. I can take it to the muffler works in my town. He's pretty good at that stuff. He won't charge me to look, only if it needs repair.
 

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