Hi all just picked up a 1998 ranger 2.5 with 115000 miles rough idle with code po 171.... vac lines intact so where is the leak?

 

P0171 Lean on Bank1
Bank 1 is the only bank on a 4cyl engine(2.5l)

Lean code means that the computer's calculated Open Time for the fuel injectors was not long enough, so its having to open the injectors longer to keep O2 sensor reported Oxygen Levels in correct range.
Usually 20% longer before it sets a Lean code

Computer is programmed for a 2.5 liter engine, so it knows exactly how much air(liters) will be pulled in at any RPM, its just Math
Computer's calculated Open Time is based on engine RPMs, throttle position, air temp(IAT) and air weight(MAF)
AND fuel pressure of 55psi, there is no fuel pressure sensor, so this is "assumed"

An intake manifold leak(vacuum leak) is the most common reason for Lean code, because MAF sensor is reporting "lighter air" so computer adds less fuel(less open time)

Dirty MAF sensor, easy to clean, should be done once a year for best MPG, dirty MAF sensor reports "lighter air"

But can be older O2 sensor, they go Lean as they age, if MPG is lower then its a "false Lean" so most likely time to change O2 sensors, 100k miles or 12 years, is life expectancy of an O2 sensor, they run out of chemicals to detect Oxygen

Pull a few spark plugs and look at the tips, light brown means good combustion, darker brown or blackish is Rich mix, change O2 first

Clogged exhaust, this causes Lean codes but would also cause power loss at higher RPMs

Steady misfires, when a cylinder misfires no Oxygen is burned up so that Oxygen goes into the exhaust and O2 sees that as Lean condition

Fuel pressure, if under 40psi then computer's calculations will be off so Lean code

And finally, the computer itself may be the cause of the Lean code, but a real long shot here, not a no shot, but a real looong shot

 

Thanks Ron... pulled two of the spark plugs on the intake side, they were kinda black and wet seemed like oil, anyway cleaned them up, looked no more than 5k on them... pain in the **** to get em out... started up and it cleared out, still a bit shaky at idle with noisy hydraulic lifters clack clack.. added 1.5 qts of maxlife auto trans fluid to the engine oil, ran for half hour .. idle smoothed out, cleared the code, seems ok for now drained the oil changed the filter added 10/30 oil...

 

Change your upstream O2 sensor, for sure, Downstream as well if funds permit

At 23 years old vehicle should be just starting on its 3 set of O2s

 

Well it looks like i bought a problem... road test oil blow by even out the dipstick... pcv is ok... looks like someone else had a go at this... and it pings WOT.... smoke out tail pipe...So i knew it had a leak before i bought it.... looks like i will be pulling the engine lol

 

You could do a compression test to confirm bad rings
But if you plan on full rebuild then doesn't really matter

You can also use vacuum gauge
Under 2,000ft elevation any idling engine should be 17"-20" of vacuum, lower can mean worn rings
Blip the throttle, open and close it quickly, drop to 0" and then goes up to 22", confirms worn rings, then back to idle level
Good rings would only drop to 2" then go up to 25", then back to idle level

 

Good info Ron but there is a lot of crankcase pressure enough to push the dipstick up and push the oil out at 60mph and oil inside the throttle body from the valve cover .... i will post pictures when i get it apart, not sure until i see whats worn in the engine, ....looks like either guides or cylinder wear/rings/carbon.... would like to get away with valve job/rings/bearings/lifters.pump... but that never happens

 

Crank case pressure can only come from rings not holding pressure well enough so blow-by gets higher, and it only takes one cylinder to cause that

Throttle body oil is from PCV and breather hoses when there is too much blow-by and oil vapor, assuming PCV Valve is working

Worn Valve guides and seals can cause excessive oil burning out the exhaust but not oil in the intake/throttle body

 

My 2011 XLT gives me this code occasionally as well. I’ve cleared the code as I’ve believed it isn’t necessarily causing any problems to the Truck. Is this truly the case? Can I just keep driving it until the next time I have the time for a more in depth service appointment?

 

P0171 is a computer calculation error based on sensor input and "assumed" data
The engine is never actually running Lean, that's not what the code means

If engine is pinging/knocking then it IS running Lean which will cause engine damage
If exhaust is smoking then engine IS running Rich, which can also cause engine damage

 

[QUOTE=RonD;2194862]Crank case pressure can only come from rings not holding pressure well enough so blow-by gets higher, and it only takes one cylinder to cause that

Throttle body oil is from PCV and breather hoses when there is too much blow-by and oil vapor, assuming PCV Valve is working

Worn Valve guides and seals can cause excessive oil burning out the exhaust but not oil in the intake/throttle body[/QUOTE

Cold start this morning getting ready to pull in garage turning it over i could tell it had a low comp, one dead cylinder start up...started pulling stuff of the engine, and lots of it lol ..looks like the head was replaced at some time along with water pump, timing belt etc.. at a guess say done a couple of years ago...spark plugs were oil fouled... hope the bores are ok

 

Lima block is a "tank"(and weighs as much) so it will be fine

 

Engine ready to pull Wednesday morning camshaft looks ok

 

 

Pulled engine today tore it down something got on top of # 4 piston and peppered it... only one piston was ok, others pistons had the landings between the rings broken, looks like rebore job deep scratches ..crank looked ok just a polish will do with new brgs.... the head looks not very old no carbon on the intakes but the seats are recessed

 

3 of the pistons cracked between the rings ??

 

All done and running problem it bogs out at full throttle, the front cat was gutted i think the second one is plugged/oil contaminated as the last owner ran it burning oil... i will check the fuel filter .... anyone in California got one of these..... got to be the cat

 

Problem was dirty MAF.... full power now.. fighting with the PO171 vacuum leak... turns out it was the gas cap... got new cat convertor front pipe