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Hi guys…ops and gal’s
I am working on a 8/98 Ford Explorer(VIN X)4.0L Calif model.
Came in with a P0171 and P0174 code. Hooked up scanner,vacuum and fuel pressure gauges. Vacuum reads 14Hgs(alt 3000ft), fuel pressure 33lbs(w/regulator plugged) 45lbs(w/regulator unplugged). But on live data my STFT LTFT both reading -100% and all 3 O2’s show a 0votage. So I tried swapping a known good O2 into it and no change. So I am thinking maybe intake or vacuum hose leak,but spraying brake clean all around I can not hear any change or hear any leaks. No signs of any exhaust leaks. Cleaned MAF no change and it reads 0.94lbs/min and changes with RPM so not sure proper reading but assume this is acceptable.
So basically before I tear this down and do a intake gasket any other suggestions of what I can check?
Oh let me add the customer said it was a progressively worsening problem.
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OK, tried all that and get no change at all in any of the trims or voltages. And maybe misread but a posative number means lean and negative means rich? So 171-174 is saying lean but O2’s are maxed at rich? reading is solid -100% 0 Volts? And all 3 are reporting same value even one being a known good O2
All 3 O2’s are heater type could there be a fuse for all 3 heaters blown and so they are not getting hot enough to report any voltages? Is that possable?
Basicly no matter what I do(unplug hoses spray carb cleaner in intake ect…) I can not cause any change in O2 readings.🙂 I have been reading my books about this. I appreciate all the sensor data and complete readings, they do help to give a way to go with this. I would test your ECT or coolant temp sensor for the computer, it may giving the computer a cold reading and the MAF may be giving the engine a hot reading and are confusing the ECM. This may help. Good Luck.
sorry on slow reply got side tracked on another car(you know how it goes…lol). I used a infraid thermo and ECT is reading correctly. The thing that confuses me is that I can in no way get any change in the O2’s readings. All 3 O2’s always read 0.00Volts and -100% no matter I cause a vacuum leak or induce carb cleaner I get no fluctuation at all. I even put a new drivers side upstream O2 in and same reading. Have checked PCV hose all around the intake with carb cleaner the intake hose between the MAF and throttle body and all vacuum hoses. I mistakenly erased the codes and noticed it hasn’t reset the 171-174(yet), but it is still running rough and now I am noticing a little bit of a backfire going on. Oh and right before I reset it there was a P0306-misfire cly 6, but it hasn’t returned either.
Going to pull up the wiring diagram and see if there is any one thing that ties the 3 O2’s together beside the computer.
Also going to do like Scotty Kilmer says and spark up a stogie and see what I can find or at least get to enjoy a cigar…lolHow are you reading the O2 values? Through the scanner or with a Volt Meter? I’d make sure the circuit they’re on has good power and ground.
Hmmm. All O2 readings being that way is a red flag for me. I could see one sensor being bad and causing those kinds of readings, but having 3 give you the same readings is suspicious. You might be dealing with a computer issue. Either the computer is not getting the correct information due to a wiring problem, or it’s pooped the bed and needs to be replaced. Thing is, you need to eliminate all other possibilities before you call the PCM bad. This means checking the wiring from the computer to the O2 sensors. Just for the heck of it, check ALL the fuses. You might have an important one that’s blown. A service manual would be your friend here. You might be able to find one online for a reasonable amount of money. Here’s a video I did on the topic.
Keep us posted.
Ya checked all the fuses even tho I had no reference saying which fuse was for what, but all checked fine. Have a haynes, but in my opinion the tree served a better purpose then this brand of manual. Went ahead and ordered a intake gasket set and set of new injector o-rings. Mean while I am researching if there is a fuse or relay that ties all 3 O2’s together. Just happened to have a 2000 Explorer that was accessible so plugged my lab top into it and it read the O2’s no problem, so I think that confirms my system is still fine. So it is definitely on the end of the vehicle. Almost tempted to pop open the ECU and see if there isn’t some sort of cold solder joint or something(maybe as a last ditch effort before buying a replacement one).
OK after searching around on different diagrams, apparently they all share orange wire which then ties into a GreyRed wire which then either is supplying voltage or ground(believe its voltage PCM controls grounds I think) to all the other engine control sensors(ie Crank sensor knock sensor ect…). Now according to the diagram this is to some sort of adjustable capacitor internal of the O2’s. But none the less it is the only thing I can find that other then the PCM they all have in common.So hopefully by following the yellow brick road(orange wire) I will find my wizard(issue).
Hope this will also fix the contradiction of a (-100)meaning it is taken away fuel because of being rich but setting a code of lean meaning it would be adding fuel.
Because if you look at the chart on this page http://en.wikipedia.org/wiki/OBD-II_PIDs the first column(for Min value) is exactly what I am seeing on my read outs(for STFT,LTFT{rows6-9}), And strangely also readouts saying what the min value is showing in the rows 14,15, and 18 which says lean… So confusing :dry: :stick:
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