timpo1981

Hi Guys,
I have a 2002 ford focus st170. It's throwing up code p1131 Lack of Upstream Heated Oxygen Sensor Indicates Lean - Bank No 1. I am getting loss of power, rough idling and poor fuel economy. After some research I cleaned the maf, plugs and checked for air leaks, but couldn't find any. The car is running slightly better but the cel came back on again with p1131. The lamda that it refers to was replaced last year then the car was stood for 11 months as i was away, so I can't see it being a bad sensor. Any ideas anyone?

Andy

oldford

Could be a lean mixture or a wrong signal from the Oxygen sensor.
Oxygen sensor may produce a lean signal when the exhaust manifold or gasket is leaking.
Lean mixture may be caused by a low fuel pressure.

Any Freeze Frame data available with the code?

timpo1981

Hi and many thanks for the quick reply. I don't have any data to show you, however I have just got hold of a diagnostic programme. What data would I be looking for?

oldford

Freeze Frame data are (sensor) values that come along with the code.
They were captured the moment the fault code was set.

You could also read out the value of the oxygen sensors and the Fuel trims when the code is present.

timpo1981

*Update*

Today i changed the O2 sensor which has made no difference whatsoever. I am still getting p1131 code, rough idling and hesitiation which is worse when hot. I have managed to get some live data info which I hope someone can shed some light on. At idle when cold the MAF reading is around 5.5 g/s and drops to around 3.5 - 4 when warm. short term fuel trim fluctuates between 0 and +35. however long term trim stays at 0! the pre cat sensor fluctuates between 0 and 0.2 and post cat goes upto 0.8. I have no idea what most of this means. Could bad coil, plugs or leads cause these problems?

Please help someone as it's driving me mad!!

oldford

The Oxygen sensor only gives a signal between 0 and 0.2 volt, which normally means a lot of Oxygen present in the exhaust gas for whatever reason.
It should be switching between 0.2 and 0.8 volt in an ideal situation.
That is also why the short term fuel trim that goes up to 35.
The Long term fuel trim is probably disabled because a fault code is present.

However, your post cat Oxygen sensor has a contradicting signal. It gives a signal of 0.8 volt, meaning (almost) no Oxygen present. Now the catalyst will be using some Oxygen, but not that much.

Did you use an original sensor for the replacement?

timpo1981

Hi and thanks for taking the time to comment.

I think its a bosch sensor that was put in. Ł98 from euro car parts. So do you think the cat could be at fault or the 2nd sensor or both? Or something else? I'm at a complete loss myself.

Andy

oldford

If the old Oxygen sensor was also a Bosch then replacing it by a Bosch sensor with the same number is not a problem. When the makes differ it could be or become a problem - usually complete with fault codes about the Oxygen sensor heater.

Without actually measuring sensor signals and exhaust levels I can't say for sure what is the problem. I have to rely on what you're telling me and by you're own admission you have not a lot of knowledge on injection systems and sensors.
It could be that it is the front Oxygen sensor that is causing the problems, or it's wiring.
I don't think you're cat is the problem. At least not yet, but the type of problems you're having (hesitations) could destroy the cat and they are expensive.

I think you should take it to a dealer or good independent garage.

timpo1981

Ok guys, I'm still having the p1131 problem. However for the past few days I have been reading up and learning how to properly use diagnostic equiptment to read live data, and have been able to rule various things out, but I am still pretty stumped as to what the problem could be, so let me run a few things by you all.

The symptoms I am having are all intermittent and include, bogging down in all gears at all rpm's hesitation, severe lack of power and high fuel consumption. Along with code p1131. I am able to clear the code and it might be a few days before it comes back or it might come back in a few hours.
With the diagnostic equiptment I have logged the following live data at idle:

Fuel status closed loop
STFT1 +36%
LTFT1 +0.8%
O2 b1 0.63v (fluctuates between 0.1 - 0.9v)
MAF 4.3g/s (Does drop to 2.8 after a while at idle and stays there)
RPM 843
Absolute throttle 18.4%

The thing is the above values happen as soon as the car goes into closed loop. The stft shoots up very fast to over +30%. If I rev the car up the stft dosen't drop at all but stays still at over 30%, which I believe rules out air leaks? Now if I set off driving after about 30 seconds the stft will drop and fluctuate between -2 to +2 as does the ltft, which I believe is normal and pretty good. The o2 voltage also fluctuates betwen 0.01 - 0.09 which I believe is also normal. If I pull over and idle again everything is fine and the trims and o2 voltage stay well within normal and the car idles smoothly. If I now turn the car off for about a minute and start again the car will be in open loop and as soon as it goes into closed loop the stft shoots up over +30 again!!! Then will drop again after a little driving!! I also noticed on the scanner that I was idling in closed loop and the car went back into open loop and the trims shot back up, so I gave a little tap on the accelerator and it went back into closed loop and the trims dropped again.

I have recently changed the cts, and thermostat, had the timing belt done and replaced the rocker gasket and put in new motorcraft plugs.

So there you have it! It certainly has me stumped! Any ideas from you guys?

oldford

The symptoms you have like severe lack of power and high fuel consumption don't seem to bother you very much, if you keep on driving the car for more than a month with these symptoms..