P0171 HIGH AND ROUGH IDLE
#1
12-09-2019
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P0171 HIGH AND ROUGH IDLE
I got a 98 3.0 ranger I just picked up and I got it home and the check engine light
popped up and the code was a P0171 lean code in bank 1. I checked for vacuum leaks and I didn’t find any and unplugged the iac while it was running and the rpms went to about 400-500. What should I replace first ? Most people have a p0171 and a p0174 with this issue but I just have the one. Any one could help it’d be greatly appreciated.
popped up and the code was a P0171 lean code in bank 1. I checked for vacuum leaks and I didn’t find any and unplugged the iac while it was running and the rpms went to about 400-500. What should I replace first ? Most people have a p0171 and a p0174 with this issue but I just have the one. Any one could help it’d be greatly appreciated.
#2
12-10-2019
Welcome to the forum
I would run a can of Seafoam or similar injector cleaner in the gas tank and then reset the code after running 1/2 a tank or so
Also check for exhaust manifold leak on passenger side, that will cause a False Lean because air is being sucked in
P0171 is Lean on Bank 1, which is passenger side of a "V" engine, this means that the computer's calculation for injector open time on that bank is more than 15% off(low) so computer is having to open the injectors on that bank longer than it calculated
Engine is never actually running Lean, well maybe for 1 second, lol, the code is just a "heads up" to let driver know of a problem
You can check spark plug tips on that bank to see if they show Rich running, darker tips, so a False lean, which can be an exhaust manifold leak or a failing O2 sensor on that bank
A clogged injector on that bank would produce the same effect, which is why you try running injector cleaner thru them
O2 sensors only "see" air, too much air is lean, too little rich
They use a chemical reaction to detect the air, and after 100k miles or so they can start to run out of the chemical needed and they start to show too much air even though its not, so false lean on that bank
Its often a good idea to change both upstream O2 sensors after 100k miles just because MPG will start to go down because of the false lean, its not much but with the price of gasoline new O2 sensors will pay for themselves over the next 100k miles with best MPG
The rough idle is misfires, of course, and when there is a misfire no air is burned/used so that air is dumped into the exhaust.................so lean condition
I would address the misfires, first by cleaning injectors and then checking spark plugs for condition inside the cylinders
I would run a can of Seafoam or similar injector cleaner in the gas tank and then reset the code after running 1/2 a tank or so
Also check for exhaust manifold leak on passenger side, that will cause a False Lean because air is being sucked in
P0171 is Lean on Bank 1, which is passenger side of a "V" engine, this means that the computer's calculation for injector open time on that bank is more than 15% off(low) so computer is having to open the injectors on that bank longer than it calculated
Engine is never actually running Lean, well maybe for 1 second, lol, the code is just a "heads up" to let driver know of a problem
You can check spark plug tips on that bank to see if they show Rich running, darker tips, so a False lean, which can be an exhaust manifold leak or a failing O2 sensor on that bank
A clogged injector on that bank would produce the same effect, which is why you try running injector cleaner thru them
O2 sensors only "see" air, too much air is lean, too little rich
They use a chemical reaction to detect the air, and after 100k miles or so they can start to run out of the chemical needed and they start to show too much air even though its not, so false lean on that bank
Its often a good idea to change both upstream O2 sensors after 100k miles just because MPG will start to go down because of the false lean, its not much but with the price of gasoline new O2 sensors will pay for themselves over the next 100k miles with best MPG
The rough idle is misfires, of course, and when there is a misfire no air is burned/used so that air is dumped into the exhaust.................so lean condition
I would address the misfires, first by cleaning injectors and then checking spark plugs for condition inside the cylinders
Last edited by RonD; 12-10-2019 at 10:07 AM.
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