AFR gauge reading too high

[charlton]

My AFR gauge has started to read too high 17+ and off the scale, you can also smell the extra unburnt fuel when the Supe is stationary. I know it should be sitting between 14-15 which it previously did.

 

What are the common causes of this/what should I be looking out for, is it something simple like the O2 sensors?

[Ian C]

Is it misfiring? The gauge can read 'lean' because the mix isn't combusting so you get a lot of oxygen come through, and you can smell the unburnt fuel as well.

[charlton]

No misfire from what I can tell, certainly doesn't sound like it or lose power at any point

[mellonman]

If it smells richer but afr show leaner it does indicate a miss fire, or you could have a hole in the exhaust sucking in air maybe

[chrispot]

try disconnecting the O2 sensor as it could be faulty and showing rich so ecu tries to lean it out. when does it show lean? is it just at idle? how does it feel driving and any loss of power?

it could be the afr gauge is faulty.

lets us know what the fault was when you have fixed it, as it could help others with the same/similar problem.

 

regards chris

[chrispot]

try disconnecting the O2 sensor as it could be faulty and showing rich so ecu tries to lean it out. when does it show lean? is it just at idle? how does it feel driving and any loss of power?

it could be the afr gauge is faulty.

lets us know what the fault was when you have fixed it, as it could help others with the same/similar problem.

 

regards chris

[Tricky-Ricky]

The default failure voltage for O2 sensors will cause the ECU to run a richer mixture for safety, and the same goes for a disconnected sensor, but the fact that the wide-band is showing lean indicates its either not calibrated correctly, or there is a misfire or air leak.

[pedrosixfour]

Would this type of fault, if a misfire was ruled out, have any ill effect on the car at WOT. I mean does the O2 sensor have any input at that point?

[chrispot]

The default failure voltage for O2 sensors will cause the ECU to run a richer mixture for safety, and the same goes for a disconnected sensor, but the fact that the wide-band is showing lean indicates its either not calibrated correctly, or there is a misfire or air leak.

 

 

when i mean faulty i mean note in spec, i don't necessary mean not working

 

so by disconnecting the o2 sensor it would/should run richer, as this is the case then it could rule out the afr gauge if it shows a rich afr when o2 is disconnected or if there is no change it could indicate a bad air leak or misfire?

 

i thought that a O2 sensor could go off tune so to speak and report a richer mixture or leaner than it really is?

[chrispot]

Would this type of fault, if a misfire was ruled out, have any ill effect on the car at WOT. I mean does the O2 sensor have any input at that point?

 

the O2 sensor is not used when the car is at WOT as the ecu goes into open loop mode and ignores the sensor and supplies fuel based on the long term trim.

[Guest pedrosixfour01]

Cheers Chris. I think my problem may have been a very undercharged battery. Charged it overnight and the rough running & strange AFR reading seems to have disappeared.

Edited May 3, 2015 by pedrosixfour01 (see edit history)

[Chris Wilson]

Would this type of fault, if a misfire was ruled out, have any ill effect on the car at WOT. I mean does the O2 sensor have any input at that point?

 

If it's a wide band and the ECU is set to run closed loop all the time it then depends on the O2 sensor and the safety features the ECU has and that the mapper has correctly enabled and mapped for.

 

The OP probably has a situation where a malfunction has caused the engine to run very rich, and it needs addressing ASAP.

 

Some aftermarket ECU's can have closed loop set all the time, but with an override to a fixed map if the O2 sensor starts giving bizarre readings. My Motec M800 is set up like that, so if one of the two widebands (one for each "half" of the engine), dies or goes crazy, the engine will revert to a fixed and safe map. It's expressed as a + or - percentage of the expected wide band readout at that load site, anything beyond those percentages and it falls back to to a none O2 sensor map. Without knowing all the intricacies it's impossible to say what the OP will be experiencing map wise. A lot of mappers prefer to just use the wideband for logging, and not read it all for skewing the map. IE, they run open loop all the time.

[Tricky-Ricky]

Would this type of fault, if a misfire was ruled out, have any ill effect on the car at WOT. I mean does the O2 sensor have any input at that point?

 

the O2 sensor is not used when the car is at WOT as the ecu goes into open loop mode and ignores the sensor and supplies fuel based on the long term trim.

 

 

As said lambda feedback is only used by the ECU during closed loop, IE idle, cruse, and up to a very minimum boost pressure,

After this point the ECUs fixed maps are used for fueling and timing, the only trims applied after this are IAT which is very minimal and knock, which is a separate default map.

[Chris Wilson]

If the car is on a stock ECU and has an FCD fitted, the first thing I would do is bypass the FCD and see what happes. Also check hoses to and shared with the MAP sensor.