7 replies to this topic

[green mini cooper]

I was wondering if anyone could advise me.

My SPi is failing the cat test because the emissions are so high. The co is 9.5% at idle and goes through the roof when the engine speed increases. The lambda reading is 0.7 - 0.8 and the HCs are around 800ppm.

I checked the Vacuum pipes first off, but could find no problems

I have changed the Cat, and then the Lambda sensor, and finally the coolant temp sensor.

Each time I got my MOT man to check the emissions and each time there was no change.


Today I had a diagnostic done on it, there were alot of faults logged (253!)

The man cleared all the faults and ran a new test, this time it said there was a fault with the Lambda sensor, it was "open loop" instead of "closed loop"

We switched off the engine and restarted it, this time it said the Lambda was "closed loop", we ran the engine at 2500 rpm for about 30 secs at which point it changed to "open loop"

Apparently this is the complete opposite of what should be happening and possibly the reason my engine is running so rich.

Any ideas? I'm getting desperate now, this has been going on 3 weeks now and my MOT runs out next Saturday!

Many thanks in advance

Matt

[Ethel]

Hardly an expert on such things but surely the ECU must fall under suspicion?

[Sprocket]

ECU is the last thing to suspect! They are tough old boots and rarely the problem.



First thing I would be looking at replacing thermostat (88c), then the coolant temp sensor, then the air temp sensor, then the lambda sensor.

First two normally the problem

Wrong stat fitted - With the engine just idling, the coolant temp can rise just enough to take the ECU out of warm up mode, once you rase the engine speed, the coolant flows around the engine better and there is more air going over the rad thus bringing the temp down and the ECU then goes back into warm up mode and open loop control, a rich condition is then present. Same can be said for a coolant temp sensor reading about 8 to 10 degrees out.

[green mini cooper]

ECU is the last thing to suspect! They are tough old boots and rarely the problem.



First thing I would be looking at replacing thermostat (88c), then the coolant temp sensor, then the air temp sensor, then the lambda sensor.

First two normally the problem

Wrong stat fitted - With the engine just idling, the coolant temp can rise just enough to take the ECU out of warm up mode, once you rase the engine speed, the coolant flows around the engine better and there is more air going over the rad thus bringing the temp down and the ECU then goes back into warm up mode and open loop control, a rich condition is then present. Same can be said for a coolant temp sensor reading about 8 to 10 degrees out.

Thanks for the replies chaps.

The thermostat has never been touched. i.e. It's the original and has never caused an issue before, althought I accept it may be knackered, but I would have thought the car would be boiling over if it were not working.

I have also fitted a new Coolant Temp Sensor on very good advice, which unfortunately hasn't made a difference.

The lambda sensor was the first thing I tried as the MOT readings were so low (0.7 - 0.8)

I have tried to think of a reason for this and only one thing has sprung out at me, that is about a year ago the car had a short cicuit which kept blowing the fuse for the brake lights and indicators. It took me days to find the trouble (and about 500 fuses!).

The wire for the reverse light switch was touching the exhaust and had melted causing a short circuit. Is there slight possiblity I could have affected the circuit in the ECU for the Lambda sensor, somehow reversing the polarity and causing it to work back to front?

Or am I completely off course and in dream land?!

How would the Air temp sensor affect proceedings?

Thanks again for the replies so far

Matt

[Sprocket]

The air temp sensor adjusts the fueling in relation to air temperature (density) therefore if the air is hot, there is less oxygen there and less fuel is added, likewise, if the air is cold, more fuel is added. These sensors fail cold so adds more fuel than is actualy required. This does not switch off the EGOC (Exhaust Gas Oxygen Correction)


to be honest mate if they guy you had doing the diagnostics cant find the problem then he is not that good. The diagnostic only gives the technician the information, its then up to the technician to diagnose the fault.

The information will be there as to what the fault is, the technician has just not picked up on it.

With the diagnostic connected

Check the coolant temp sensor is reading within a couple of degrees, using a calibrated digital thermometer.

Check the air temp sensor is reading within a couple of degrees, using a calibrated digital thermometer.

Check the operation of the lambda sensor by clamping the fuel flow line momentaraly and watch the volts go low, clamp the fuel return line momentaraly and watch the volts go high.

Drive the car with the diagnostic still connected and watch the engine temp while driving, if its well below 88, with a good coolant sensor, the thermostat is duff.


Remember that the instant you move the throttle, acceleration enrichment is on and EGOC is off momentaraly during this engine condition, but will not last more than a second.


I still think you should revisit the coolant temp sensor and thermostat, the diagnostic should show this with a drive out.


What were the logged faults??




If you can prove al the above to be good than the only other thing to consider is the wear on the valve seats or valve clearancies. This does not turn off EGOC

Edited by Mini Sprocket, 08 September 2007 - 11:25 PM.

[green mini cooper]

The air temp sensor adjusts the fueling in relation to air temperature (density) therefore if the air is hot, there is less oxygen there and less fuel is added, likewise, if the air is cold, more fuel is added. These sensors fail cold so adds more fuel than is actualy required. This does not switch off the EGOC (Exhaust Gas Oxygen Correction)


to be honest mate if they guy you had doing the diagnostics cant find the problem then he is not that good. The diagnostic only gives the technician the information, its then up to the technician to diagnose the fault.

The information will be there as to what the fault is, the technician has just not picked up on it.

With the diagnostic connected

Check the coolant temp sensor is reading within a couple of degrees, using a calibrated digital thermometer.

Check the air temp sensor is reading within a couple of degrees, using a calibrated digital thermometer.

Check the operation of the lambda sensor by clamping the fuel flow line momentaraly and watch the volts go low, clamp the fuel return line momentaraly and watch the volts go high.

Drive the car with the diagnostic still connected and watch the engine temp while driving, if its well below 88, with a good coolant sensor, the thermostat is duff.


Remember that the instant you move the throttle, acceleration enrichment is on and EGOC is off momentaraly during this engine condition, but will not last more than a second.


I still think you should revisit the coolant temp sensor and thermostat, the diagnostic should show this with a drive out.


What were the logged faults??




If you can prove al the above to be good than the only other thing to consider is the wear on the valve seats or valve clearancies. This does not turn off EGOC

I knew you were going to say that! I've been reading your replies for the last 3 weeks going back over a long time on this site!!

Unfortunately the techie who plugged it in was en route to visit his very sick father, so was reluctant to spend more than about 20 mins probing, a fact which I wasn't willing to push as he was doing me a favour in the first place.

We don't know what the faults were, as you say if we'd spent more time probing then it would have come to light.
All I was hoping was if the diagnostic could pin point a fault, then someone in the know be able to help me to recify the problem.

Thanks for taking the time to reply. I'm getting it booked in to a garage with a good reputation tomorrow.

Edited by green mini cooper, 09 September 2007 - 07:48 AM.

[green mini cooper]

The problem was the MAP sensor. Although I had changed the vacuum pipes recently, the damage had already been done.

£45 Job done!

Thanks for the all the advice!

Matt

[Sprocket]

Now that is interesting, The MAP sensor usualy causes alsorts of bad running issues more noticable than just running rich.

Also, £45 fixed, is a bloody good price, the sensors cost that alone and it needs soldering onto the board, it takes about half an hour just to get into the box!

fault noted

Edited by Mini Sprocket, 14 September 2007 - 08:45 PM.