code p0171
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code p0171
I have a 1997 ford ranger coming up with a code p0171. Lean on bank one. It has a 4.0l engine 4x4 5 speed trans. I have changed all 3 of my ox. sensors, cleaned my maf, cleaned my throttle body. I also changed my egr valve and air charged temp sensor. i am stumped can anyone help. I also sprayed my intake and plenum to see if there was an airleak there but nothing showed up. I clear the codes than about 10kms later the code comes back up.
Last edited by info_napl; Feb 17, 2003 at 05:16 PM.
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From: suburban atlanta
code p0171
The O2 sensors detect oxygen in the exhaust. They put out voltages from .1 to .9 approximately. (Low is lean is my mnemonic)
As the engine runs, there can be excess O2 in the exhaust when the mix is lean and when there is a misfire. The misfire leaves the O2 uncombined with the fuel, so it is still there.... and measured.
On the older cars, the ECM was too dumb to figure out that there was misfire, just that the O2 was reading low...lean. The OBD-II cars, such as yours should be, detect misfire in specific cylinders by using the acceleration or deceleration in rpm as measured by the CKP sensor, and can identify it down to a specific cylinder.(At least that's how I think they do it)
I would inspect the EGR for working properly as its flow volume is considered by the ECM when calculating how much fuel to spritz. I have also heard of the 4.0l engines having bad gaskets on the intake, both upper and lower O-ring style gaskets. If it is just one bank, then I'd have a hard time looking at the MAF and other parts out that far... They'd hit both cylinders I'd think. I have read of the EGR passages getting full of crud, and letting most of the inert gas into one cylinder, causing it to run poorly. For sure, the wires to the O2 sensors are in good shape, right? If damaged, they can mislead the ECM with false values.
just my opinion.
tom
As the engine runs, there can be excess O2 in the exhaust when the mix is lean and when there is a misfire. The misfire leaves the O2 uncombined with the fuel, so it is still there.... and measured.
On the older cars, the ECM was too dumb to figure out that there was misfire, just that the O2 was reading low...lean. The OBD-II cars, such as yours should be, detect misfire in specific cylinders by using the acceleration or deceleration in rpm as measured by the CKP sensor, and can identify it down to a specific cylinder.(At least that's how I think they do it)
I would inspect the EGR for working properly as its flow volume is considered by the ECM when calculating how much fuel to spritz. I have also heard of the 4.0l engines having bad gaskets on the intake, both upper and lower O-ring style gaskets. If it is just one bank, then I'd have a hard time looking at the MAF and other parts out that far... They'd hit both cylinders I'd think. I have read of the EGR passages getting full of crud, and letting most of the inert gas into one cylinder, causing it to run poorly. For sure, the wires to the O2 sensors are in good shape, right? If damaged, they can mislead the ECM with false values.
just my opinion.
tom
Last edited by tomw; Feb 20, 2003 at 07:41 AM.
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code p0171
Check the wiring, checks out ok. The funny thing is the code only comes up while driving in town at 50kms per hour or less. On highway nothing comes up. I drove 300kms this weekend a little at 100kms per hour and made stops in between and drove speeds around 80. No light came on. Drove aroung the city, about 10kms and light comes on.
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