1998 Lexus GS400 - P0172 - Runs Rich
06-19-13, 02:40 PM
#1
1998 Lexus GS400 - P0172 - Runs Rich
Hello all,
Recently after changing my motor mounts, I have noticed that my engine runs rougher than before. The car will sometimes "stumble" into running, when trying to start the engine. It occasionally bogs down with light throttle at low RPM, usually accelerating from a stop. A few days ago, it got so bad that I received a CEL of P0172. I truly don't know what to do next. I've tried two different MAF sensors to no avail, the spark plugs were replaced 20k ago, and the fuel filter only 30k ago. The throttle body has also been cleaned. What should be my next plan of action? Thanks in advance!
Recently after changing my motor mounts, I have noticed that my engine runs rougher than before. The car will sometimes "stumble" into running, when trying to start the engine. It occasionally bogs down with light throttle at low RPM, usually accelerating from a stop. A few days ago, it got so bad that I received a CEL of P0172. I truly don't know what to do next. I've tried two different MAF sensors to no avail, the spark plugs were replaced 20k ago, and the fuel filter only 30k ago. The throttle body has also been cleaned. What should be my next plan of action? Thanks in advance!
06-20-13, 03:48 PM
#3
Thank you very much for your response! Here's everything my scanner showed me:
STFT - Bank 1: 3.1%
LTFT - Bank 1: 9.3%
STFT - Bank 2: 1.5%
LTFT - Bank 1: 9.3% ( Don't know why it shows Bank 1 LTFT twice)
Bank 1 - Sensor 1 O2S Output: 0.715V
Bank 1 - Sensor 1 STFT: 2.3%
Bank 1 - Sensor 2 O2S Output: 0.070V
Bank 1 - Sensor 2 STFT: 99.0%
Bank 2 - Sensor 1 O2S Output: 0.085V
Bank 2 - Sensor 1 STFT: 3.1%
Bank 2 - Sensor 2 O2S Output: 0.055V
Bank 2 - Sensor 2 STFT: 99.0%
STFT - Bank 1: 3.1%
LTFT - Bank 1: 9.3%
STFT - Bank 2: 1.5%
LTFT - Bank 1: 9.3% ( Don't know why it shows Bank 1 LTFT twice)
Bank 1 - Sensor 1 O2S Output: 0.715V
Bank 1 - Sensor 1 STFT: 2.3%
Bank 1 - Sensor 2 O2S Output: 0.070V
Bank 1 - Sensor 2 STFT: 99.0%
Bank 2 - Sensor 1 O2S Output: 0.085V
Bank 2 - Sensor 1 STFT: 3.1%
Bank 2 - Sensor 2 O2S Output: 0.055V
Bank 2 - Sensor 2 STFT: 99.0%
06-20-13, 04:23 PM
#4
Alright, so, what I need you to do is see if Bank 1 Sensor 1 stays at or around .715V, or does it cycle. Even with rich codes, the voltage from that sensor should vary at least some - a full rich sensor will read close to .90 volts, and if it is stuck around .715V, then the sensor is not working properly... Ideally what we want to see of a properly working sensor would be voltage sweep from .1 to .9 volts cycling once every second or two...
06-20-13, 04:55 PM
#6
Does the car have any modifications at all??? system rich is fairly rare... two most common causes of system rich is a leaky fuel injector or incorrect fuel pressure...
what year is your car? On the GS4's, I don't know if they ever had a conventional fuel pressure regulator, or if it is returnless, but if I know the year, I'll find out... check vacuum lines - a vacuum line off the fuel pressure regulator will cause system rich...
actually, not that I look at it again... are you sure those are positive numbers for the fuel trims? system rich should be pulling fuel and have negative numbers...
06-20-13, 05:03 PM
#7
Well, that generally means that the O2 sensor is working properly...
Does the car have any modifications at all??? system rich is fairly rare... two most common causes of system rich is a leaky fuel injector or incorrect fuel pressure...
what year is your car? On the GS4's, I don't know if they ever had a conventional fuel pressure regulator, or if it is returnless, but if I know the year, I'll find out... check vacuum lines - a vacuum line off the fuel pressure regulator will cause system rich...
actually, not that I look at it again... are you sure those are positive numbers for the fuel trims? system rich should be pulling fuel and have negative numbers...
Does the car have any modifications at all??? system rich is fairly rare... two most common causes of system rich is a leaky fuel injector or incorrect fuel pressure...
what year is your car? On the GS4's, I don't know if they ever had a conventional fuel pressure regulator, or if it is returnless, but if I know the year, I'll find out... check vacuum lines - a vacuum line off the fuel pressure regulator will cause system rich...
actually, not that I look at it again... are you sure those are positive numbers for the fuel trims? system rich should be pulling fuel and have negative numbers...
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06-20-13, 05:09 PM
#8
Alright, a couple more things to check - what does the ECU report the coolant temp and intake temp as??? Do they seem accurate for the outside temp when the engine is cold? Does the coolant temp go up to about 185-190 when the car is fully warmed up?
06-20-13, 07:47 PM
#10
So, yours doesn't have an external fuel pressure regulator - it is inside the fuel tank... I found one instance of a similar issue someone else had on a GS400 and their solution was fuel injector cleaner in the gas tank and resetting the pcm...
Doesn't seem like a viable solution, but if you have an injector gummed up, could potentially work... what happens is if an injector is partially clogged, the fuel doesn't atomize well and it doesn't burn well... lack of power and a rich condition is the result...
Doesn't seem like a viable solution, but if you have an injector gummed up, could potentially work... what happens is if an injector is partially clogged, the fuel doesn't atomize well and it doesn't burn well... lack of power and a rich condition is the result...
06-21-13, 04:14 AM
#14
mitsuguy, after using a MAF sensor I had laying around, I cleared the code to see if it would come back. This was about 3 days ago. The CEL has yet to come back on, but the car is still running kinda rough. It's not as bad as before, but it is still there. In light of this, I purchased a brand new MAF sensor from the dealer to see if would help, thinking that both of the MAFs I had at home were bad. This didn't help the situation one bit. I wonder if it's a coilpack starting to go bad on bank 1?
06-21-13, 06:35 PM
#15
mitsuguy, after using a MAF sensor I had laying around, I cleared the code to see if it would come back. This was about 3 days ago. The CEL has yet to come back on, but the car is still running kinda rough. It's not as bad as before, but it is still there. In light of this, I purchased a brand new MAF sensor from the dealer to see if would help, thinking that both of the MAFs I had at home were bad. This didn't help the situation one bit. I wonder if it's a coilpack starting to go bad on bank 1?
check for obstructions in the intake as well - a severely restricted air filter or inlet could cause this, though usually set codes for both sides...