Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Very high fuel trims, no fault codes
1 week 1 day ago - 1 week 1 day ago #65940
by Bifojo28
Very high fuel trims, no fault codes was created by Bifojo28
Hi, I'm trying to diagnose a problem on a Renault Clio 1.2 16v, the idle is unstable, smell of gas from the exhaust, when driving from cold I can see white smoke and sometimes slightly blue coming out. When coasting downhill, pressing the accelerator sometimes throws a visible white smoke cloud. The car is not loosing coolant.
I've already check for leaks with a smoke machine and didn't find anything.
This is at idle, not sure what happened with the O2 sensor there at the beginning.
Further tests and watching graphs I'm almost 100% sure that it is a fuel delivery issue because the STFT goes up when the engine rpm increases. It slowly climbed to 65% at 2200rpm BUT at 2700rpm it decreased to 52% then hovered around 60%. Perhaps a partially blocked injector too ?
I also unplugged the upstream O2 sensor and ran the engine for a minute just to see what the STFT would be, and it was fixed at 50% and the O2 at 0.51v.
What does this mean ? Shouldn't it go to 0% or near zero, why straight at 50% ?
I then plugged back the O2 sensor and unplugged the MAP sensor (this engine only has a MAP sensor) it turned on the check engine light and defaulted to 10 kpa, the O2 sensor at first was fixed at 0.51v (STFT fixed at 50%) took like 20 seconds to react, then it increased to 0.82v, the STFT at the same moment dipped to 33% and then spiked between 32-40% in correlation to the O2 sensor activity.
MAP sensor is almost within spec, it's reading at idle 27-28 kpa, the manual says 35kpa +/- 5kpa. I already cleaned it with contact cleaner, perhaps that made it worse can't remember now.
Do you consider it faulty or enough deviation to cause the high fuel trims?
I did some throttle blips.
The downstream O2 sensor seems to be dead, it's giving an intermittent open circuit and when it does work it reads the same as the Upstream or just reads low voltage.
I read that it doesn't affect the fuel trims, it only monitors the cat efficiency, I have this thought that the engine is running in this lean condition for months or perhaps years (the car is not mine and is neglected), it damaged the catalytic converter and the sensor and probably something more.
EDIT: Added photos to better show the problem.
I've already check for leaks with a smoke machine and didn't find anything.
This is at idle, not sure what happened with the O2 sensor there at the beginning.
Further tests and watching graphs I'm almost 100% sure that it is a fuel delivery issue because the STFT goes up when the engine rpm increases. It slowly climbed to 65% at 2200rpm BUT at 2700rpm it decreased to 52% then hovered around 60%. Perhaps a partially blocked injector too ?
I also unplugged the upstream O2 sensor and ran the engine for a minute just to see what the STFT would be, and it was fixed at 50% and the O2 at 0.51v.
What does this mean ? Shouldn't it go to 0% or near zero, why straight at 50% ?
I then plugged back the O2 sensor and unplugged the MAP sensor (this engine only has a MAP sensor) it turned on the check engine light and defaulted to 10 kpa, the O2 sensor at first was fixed at 0.51v (STFT fixed at 50%) took like 20 seconds to react, then it increased to 0.82v, the STFT at the same moment dipped to 33% and then spiked between 32-40% in correlation to the O2 sensor activity.
MAP sensor is almost within spec, it's reading at idle 27-28 kpa, the manual says 35kpa +/- 5kpa. I already cleaned it with contact cleaner, perhaps that made it worse can't remember now.
Do you consider it faulty or enough deviation to cause the high fuel trims?
I did some throttle blips.
The downstream O2 sensor seems to be dead, it's giving an intermittent open circuit and when it does work it reads the same as the Upstream or just reads low voltage.
I read that it doesn't affect the fuel trims, it only monitors the cat efficiency, I have this thought that the engine is running in this lean condition for months or perhaps years (the car is not mine and is neglected), it damaged the catalytic converter and the sensor and probably something more.
EDIT: Added photos to better show the problem.
Last edit: 1 week 1 day ago by Bifojo28.
Please Log in or Create an account to join the conversation.
Time to create page: 0.241 seconds