- FORD/FIESTA/1.4 ZETEC/2003 CAT EFFICIENCY & RUNNING LEAN ERRORS Archived Message
Posted by George Georgiou
on June 8, 2008, 12:29 am
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I know there is a similar problem reported before but no solution found as yet to Fiesta with Cat efficiency problem Looked at this Fiesta about a week ago and reset codes to clear MIL light. Scanner gave PO171 system too lean PO420 Cat system efficiency below threshold PO131 O2 sensor circuit low voltage (bank 1 sensor1) Two days later customer reported MIL back on. Scanned today and found same errors as above + one more PO133 O2 sensor circuit slow response (bank 1 sensor 1). Customer did replace both pre & post O2 sensors himself when the MIL first came on some time before I first saw the vehicle. I think he used a handheld scanner and got the O2 codes so assumed it must be those sensors. He assumed he had fixed the problem by replacing )2 sensors and could not reset the MIL so he left it until I opened my big mouth to offer my 'expert' help to solve his MIL problem. The sensors were obtained from Fuel parts, Zirconia type. The pre O2 was a straight swop and the post was a universal one which had to be wired in as per instructions. After clearing the faults today the engine was tested with PICO and from cold to hot the pre O2 was stuck on 0.15 volts and the post O2 was stuck on 0.9 volts. At this time having cleared the faults the system was still showing error PO171 System too lean. The heater circuits were both ON on the scanner and also when scoped. The sensor output was scanned directly on the black wire from each of the sensors. I cannot get the pre O2 to switch correctly , it is stuck to lean indication except on some brisk revving when it responds 2-3 seconds after opening the throttle but only briefly switching to about 0.7 volts and then falling back to lean condition. The post O2 is stuck at 0.9, except when I disconnected it and it showed 0.45 volts on the scanner (ECU default I guess) and then re-connecting it I saw it drift toward 1.0 volts , reaching 0.9 volts when re-connected. MAP sensor scoped with good response up to 4.2 volts on WOT. ECT showed no dropouts and correct temp reading with fan on at 103 degrees and off at 93 degress from memory. Secondaries scoped all showing good coil performance and switching with ping lines to 12KV and burn times all same about 1.3 ms on idle. No misfiring on idle or revs and customer reports engine runs very well except for this MIL light coming on. Gas analyser idle , engine hot, shows : CO 6.64% CO2 9.13 % LAMDA 0.89 HC 325 ppm O2 2.36 % NOX 100 ppm not sure what is going on here but these figures are an emmisions failure ?, maybe indicating a misfire perhaps , or possibly an air leak giving lean condition. Have sprayed carb cleaner on and around manifold but no changes. Removed all sparks and re-gapped to 1.3mm all were about 1mm gap. Problem with all sparks is metal body was badly corroded and evidence of water/coolant immersion was present on plugs and on bottom parts of leads (rust coloured deposits). No explanation for this except some kind of flooding? The spark heads were all good showing good spark burn with no oil fouling or glazing from running lean. Vacuum testing showed healthy 22 inches and revving the engine gave desired drop in vaccuum and recovery down to 25 inches then back to a very steady 22 inches. I guess I can rule of valves sticking . Oil looks clean and vehicle serviced when purchased back in January although I have my doubts as to whether plugs got changed. I suppose the clue to this problem is in the gas analysis and I will try and learn for myself what the figures mean , however the wise on this forum will no doubt be able to help on these figures. I suspect I may have a fueling issue and I need to carry out a fuel pressure and flow test (even though car drives OK) . Also may need to do a compression test as well. Customer has the vehicle and no doubt I will get another chance to find the problem next week once the light comes on again. Could all this be down to 2 or all three of the O2 sensors being faulty? I put back the original O2 on the pre- position and it still showed same lean condition as new sensor. Help please.  George |