CEL on and driving me crazy..... - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 01-02-2011
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CEL on and driving me crazy.....

So my CEL has been on a few weeks. Took it to autozone and the code reader gave me P0171 and P0174, . my truck is a 1997 Ford Ranger XLT 4.0 V6. Ive read on here another thread that had the same problem but I believe was on a 2003 Ranger. My question is can anyone tell me where to find the "cracked" elbow on my truck? Or if this is a common problem on Ford Rangers before 2000. And I have changed the MAF sensor, CEL stayed off two days then came back on. Gas Mileage slipping. Thanks
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Old 09-23-2017
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the CRACKED ELBOW is the hose that runs from the intake manifold to the brake booster

also check the rubber seal on the fuel tank gas cap

clean it and apply some lithium grease to both sides of the seal

this method will put oils back into the seal and make it swell to seal out air
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Old 09-24-2017
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Elbow issue was on Rangers with 4.0l SOHC engines(2001-2012), you have a 4.0l OHV engine(1990-2000), yes common issue on 2001 and up, not on earlier 4.0l OHV

P0171 and P0174 codes mean the computers calculation of air/fuel mix is too low for the amount of air it is reading coming into the engine
Often called "Lean codes" but engine is never running Lean, lol, so..............grain of salt with any "codes"

The Computers main purpose is "on the fly" air/fuel ratio calculations, it gets the air flow data and then uses the 14.7:1 air:fuel ratio for gasoline engines to add the correct amount of gasoline to the reported amount of air, by opening the fuel injectors for a specific time, milliseconds
It then gets the "burn report" from each side of the engine from that sides O2 sensor
It then "trims" the open time for the injectors on that side of the engine to get correct Oxygen Levels in that sides exhaust.
If open time for the injectors gets too high(or too low) then computer will set code(s) and turn on CEL to let driver know it's calculations are too far off

The fact that BOTH sides(banks) of the engine are showing low fuel mix calculations means problem is common to BOTH sides

Air flow data starts at MAF(mass air flow) sensor on the air cleaner, it can be cleaned, and should be cleaned every 5 years or so, more often in dusty areas

The air tube from MAF to upper intake on the engine must have a tight seal, or MAF sensor won't be correct in reporting ALL the air coming in, leaked air is unreported air so computer is basing its air/fuel mix on "bad data", garbage in garbage out
Same for a Vacuum leak, unreported air is leaking in.
To effect BOTH sides of the engine it must be upper intake vacuum leak.

Simple test for Vacuum leak
Warm up the engine first
Let it idle and unplug the 2 wire connector on the IAC(idle air control) Valve, its on the upper intake near throttle plate
When IAC Valve is unplugged the valve will close and idle RPMs should drop to 500 or engine may even stall, either is GOOD, it means no vacuum leak

If idle stays high then there is a leak, leave IAC valve unplugged and pull off each vacuum hose, one at a time, from the intake and plug that port with your finger, when Idle drops you found the hose or device with the leak.


If idle does drop to 500 or engine stalls with IAC valve unplugged then there is no vacuum leak.
So either the MAF sensor is dirty/failing or its air tube to intake is leaking

OR..............fuel pressure is low
There is no Fuel Pressure sensor, Computer is programmed to expect 35psi pressure in 1997(1998 changed to 65psi)
So if fuel pressure gets down to 20 or so PSI then each time computer opens an injector to add fuel, less fuel flows in, so computers calculations are off, and it sets the codes
Dirty fuel filter can lower pressure, should be changed every 5 years as well
There is a Fuel Pressure Regulator(FPR) on the lower intake by alternator, has Fuel Return hose attached and a vacuum hose
This is just a spring loaded valve, keeps pressure under 45psi, if it starts to leak then pressure will drop below 20psi, and fuel is just flowing back to the gas tank so no external leak, just lower pressure


And ultimately the computer relies on the two upstream O2 sensors to tell it the Oxygen levels in the exhaust to determine if the fuel burn was lean or rich, these use a chemical reaction to detect oxygen, so will wear out just like batteries do, 100k miles is recommended change period for upstream O2s, downstream last twice as long
This is NOT your problem, because BOTH O2s would have to fail at the same time, which is extremely long odds
Just mention it because as O2s get older they do lower MPG so new O2s will pay for themselves in fuel savings over the next 100k miles

Last edited by RonD; 09-24-2017 at 02:40 PM.
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Old 09-24-2017
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Quote:
Originally Posted by cheese_man View Post
the CRACKED ELBOW is the hose that runs from the intake manifold to the brake booster

also check the rubber seal on the fuel tank gas cap

clean it and apply some lithium grease to both sides of the seal

this method will put oils back into the seal and make it swell to seal out air
I think you might mean silicone grease, not lithium?
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Old 09-24-2017
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silicone grease will work as well , but not as common as lithium grease

lithium grease is not petroleum based and will not eat rubber
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Old 09-24-2017
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Quote:
Originally Posted by cheese_man View Post
silicone grease will work as well , but not as common as lithium grease

lithium grease is not petroleum based and will not eat rubber
I think you're thinking of silicone grease, lithium is typically petroleum based.
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