Diagnosing overfueling

[RAVEN]

Hi!

I have suspected for some time that my clio 197 is running too rich. There is a strong gasoline smell when it stays with engine running, exhaust tips quickly goes to black and it seems to have less power. The only information from the computer was flashing engine managment light, but it appears only one time and for very short time.

Is there a quick method to check does it really overfueling? I have BT OBD reader and I can use some app like torque or pyclip, but I do not know for what I should search (lambda readigns, injection corrections, what values)? If it really works too rich, where to look for reason is there any easy way to test coils/injectors/plugs?

 

[Jack Maxwell]

Use the ODB reader whilst driving and monitor the short term fuel trim as well as voltage from the lambda sensor. Lambda sensor is probably faulty and causing the fuel trim to over fuel.

 

[wootwoot]

Yep check if the signal fluctuates up and down. Also check the long term fuel trim while on the freeway. That signal is very specific to the O2 sensor and should be rock solid stable for the most part.

 

[RAVEN]

Hello, many thanks for the information about which parameters to look at, Jack Maxwell and wootwoot! Today I made some logging and I think it is not looking great. Both short term and long term trim figures are fluctuating a lot and are going pretty high (so I assume too much fuel is being added), but the first O2 sensor is looking good on idle (or so I think; it's fluctuating between 0 and 0.7). The graph from the second O2 sensor does not have that kind of shape, but if I recall correctly, the second one does not make any corrections; it is only for checking the cat, am I correct? Below you can see screenshots from the torque app:

(Looking at the screenshots now, it looks like the Y value for long term and short term trim is wrong (it does not match the respective point of the axis), take it into consideration based on the values which torque is highlighting)

Stationary on long idle:


Stationary with 3k RPM after long idle:


Short and long term trim just after driving on idle:


All parameters just after driving on idle:


And during driving at steady 2,5k RPM:


How should I interpret those logs? My understanding is that the injectors themselves are fine, i.e. they are not injecting too much fuel, because if they were, the correction values would come out negative. It looks as though something was causing too much fuel to be injected, but I don't know what it could be. If the data is not clear I can also upload screen recordings instead of screenshots. What to do next, where to search for the root cause of the issue?

 

[Jack Maxwell]

I've found a couple videos form when I was logging my issue.

First video is from when the lambda sensor was faulty. You can see when im on the throttle the lambda voltage flat lining at 0v and the fuel trim going to 99% as it doesn't know whats going on.

In the second video this must be after I fitted a new sensor. You can see the voltage fluctuating nicely as well as the fuel trim. The short term will fluctuate a lot but the long term will be more steady.

This should help you seeing the difference between a healthy and unhealthy lambda.

 

[RAVEN]

Thanks for your recordings Jack Maxwell! Based on that I think that my first O2 sensor is working correctly, the graph looks exactly like on your second clip. However, the second O2 sensor does not look like that, it is living its own life. But the question is if the second O2 sensor can influence fuel trims; as far as I know it cannot. So, do you have some ideas where to search next?

 

[turkie172]

Over fuelling look at the spark plugs and see their condition if the car has any sort of fault that might not bring up an emission light the car can default to a rich condition for safety. I had a issue of stuttering as if a fuelling problem I bought one of the RS tunner's which can log and show faults a bit easier than the Renault clip I found while driving I had a short circuit on the first lambda that reset if I turned the engine off and on, did not show up at idle and did not bring up any dash warning lights.