working on 95 Mercury Cougar V8 4.6l OBDII showing MIL 1131. Have tested components (using voltmeter) down to oxygen sensor. This car has heated oxygen sensors, each front sensor has 4 wires to it, 1 black, 2 white, 1 grey or orange depending on the side. Does anyone know which wire is the signal wire?
Thanks
Just a few random thoughts, here...
P1131 is indicating that the system is correcting for a lean condition... when someone is down to testing O2 sensors.... I am giving them funny looks.
When faced with a lean code, the very first thing you need to do is see what the other bank is doing. Look at both long and short term fuel trims... Is the other bank into major fuel corrections but not far enough to set a code yet? This is an important consideration. LTFT, as a "rule of thumb", generally has to be at a fuel correction of 25% or more before you will get an light and code.
If all you have is a code reader, you are nearly trapped.... a good scan tool with graphing capability will allow you to monitor engine parameters and decide if your P1131 is because of lean mixtures or (a very rare - VERY, VERY rare) O2 sensor failure.
Fuel pressure.... all too often we see some unwitting soul test fuel pressure sitting in the driveway with the motor idling... I see "trained techs" attempting this same fools errand way too often. If you actually did test fuel pressure properly (why do I feel a nagging doubt?) it would have been on a road test and in a manner that would maximize the fuel system demands. If fuel pressure was so bad that it would show in a no load condition, you would have immense drivability concerns. Sometimes we see someone test fuel pressure by pushing in on the Schraeder valve.... it's never been a good indication for me...... and I been doing this crap for "some time".
Freeze frame data... "common" code readers cannot access freeze frame data.. Shit... most people don't know it exists and many that do don't know how to use it... When some codes set, they may be accompanied by freeze frame data... (mixture codes will nearly always generate freeze frame data). The amount of info given will vary from car to car, year to year and concern to concern. At the very least it will include engine rpm, vehicle speed, coolant temp, TPS, runtime and other engine basics to help the tech recreate the conditions that set the code in the first place. I can't place enough value on this info and how it can help us avoid unecessary problems.
O2 sensor wiring... When we refer to the factory wiring diagrams, all of the wiring colour codes are given for the harness in the car... not for any component pigtails. Describing the colours for these pigtails is going to get real rough - If you purchase a replacement pigtail from Ford, you will notice that all of the wires supplied with the pigatil are the same colour.. The two white wires you describe are, most likely, the wires to the heater... any wire with a hint of black is very possibly a return wire and the other will likely be the signal wire.... If you look at the car side of the connector, things should get a little easier...
My first initiation into electronic fuel injection was in the early 70s with VW, Porsche and Audi.. in the 80's this became even more vivid. In all of those years, I have replaced very few O2 sensors... and those usually for burned wiring harnesses...
You might check here
Possible bad o2 sensor. In a perfect world they would last forever but due to fuel contamination they wear out over time. By 120,000 miles most have a degraded voltage /time switching signal.
TSB 98-23-10 Dirty MAF can cause this code. Clean it, clear the codes and see if it comes back. I like to try the easiest cheapest stuff first... HTH Ben
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