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New CEL/DTC, looks like a bad o2 or precats

KAOS_3.0

Hard-core CEG'er
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May 16, 2008
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so, I'd been tripping the p0171, p0174, and p0161 for a while and just resetting the learnable memory because the consensus was that it was a bug in the tune, but I decided to leave it alone for a while and see what else came up, and I tripped a p0420, so with all of these codes together, I'm going to say it looks like either the precats or the down draft o2's are toast, or maybe both...

if you remember, when the coil was mis-wired, it was shoveling enough fuel into the mani-cats for them to glow orange at the elbow below the precat (where the downdrafts are...) so I dont think it's really any surprise that something got toasted down there

so, would MIL eliminators fix my problem for now? like, untill I can afford headers? or would I still need to replace the 02 for them to work right?

also, what about o2 spacers? I know thats a junky way to go, but would it get it to run better cheaply for the mean time?

thanks guys.
 
You have to ignore the 0420 until you verify the integrity of the upstream O2 on bank 1.

The 0161 is pretty straightforward. You need a new bank 2 downstream O2 unless there is a possibility of a wiring issue.

The 0171 & 0174 are a result of readings from your upstream O2's and would normally indicate an actual fuel issue, especially given the fact that they are BOTH present. That is probably why people were blaming your tune. However, given your previous problem of overfueling, I would lean more toward bad sensors, ruined by your overfueling problem.

Spacers on your downstream O2's have no possibility of helping your situation. And you definitely do NOT want to put spacers on your upstream O2's, (that is going to give the PCM false readings), unless you've got a way to monitor your actual A/F on each bank, and adjust accordingly.
 
thanks man, that cleared some things up for me. so do you know if the taurus upstreams are the same? I'm under the impression that o2's all give the same voltage readings for the same temperature ranges right? I'll go look at the two I have in those taurus manifolds and see, I believe they were the same as either my up streams or down streams, hopefully, they are the same as the upstreams and I can pop them in.

on another note, I believe I may have a slight exhaust leak, probably at the head, and I'll venture to say, probably on the back bank, since it seems to get mighty hot back there. so I'm probably going to have to get back there and re-torque the back manifold.
 
thanks man, that cleared some things up for me. so do you know if the taurus upstreams are the same? I'm under the impression that o2's all give the same voltage readings for the same temperature ranges right? I'll go look at the two I have in those taurus manifolds and see, I believe they were the same as either my up streams or down streams, hopefully, they are the same as the upstreams and I can pop them in.

on another note, I believe I may have a slight exhaust leak, probably at the head, and I'll venture to say, probably on the back bank, since it seems to get mighty hot back there. so I'm probably going to have to get back there and re-torque the back manifold.

yea an exhaust leak would trip a code.
 
If you have an exhaust leak fix that first. Also make sure that you don't have any vacuum leaks. To me two lean codes (for both the left and right bank) screams lean, not that you have two bad 02s...

As far as the sensors go they are different. The upstream is what ford calls an oxygen sensor and the downstream is called a catalyst monitor. Usually one has a blue connector and the other has a green connector. They usually have a tang in a different location...
 
Also make sure that you don't have any vacuum leaks.
Great advice that completely slipped my mind. A vacuum leak at the UIM would be much more common than BOTH sensors going bad, AND could have contributed to your initial overfueling problem.

As far as the sensors go they are different. The upstream is what ford calls an oxygen sensor and the downstream is called a catalyst monitor. Usually one has a blue connector and the other has a green connector. They usually have a tang in a different location...
This is true of name and tang location. And depending on model year, some have a square connector for the upstreams as opposed to the more common round one. But their differences end there. Their functionality in monitoring O2 content of the exhaust is the same for a given model. Consequently, I have crossed downstream to upstream a number of times - just grind down the tang on the connector, (the wire locations are the same). There ARE subtle differences that CAN cause slightly different readings when crossing sensors between models... learned that the hard way. :blackeye: I wouldn't expect any issues going from Taurus to Contour, though I would definitely watch for any difference in sensor readings, when swapping them out - just in case.
 
Great advice that completely slipped my mind. A vacuum leak at the UIM would be much more common than BOTH sensors going bad, AND could have contributed to your initial overfueling problem.


This is true of name and tang location. And depending on model year, some have a square connector for the upstreams as opposed to the more common round one. But their differences end there. Their functionality in monitoring O2 content of the exhaust is the same for a given model. Consequently, I have crossed downstream to upstream a number of times - just grind down the tang on the connector, (the wire locations are the same). There ARE subtle differences that CAN cause slightly different readings when crossing sensors between models... learned that the hard way. :blackeye: I wouldn't expect any issues going from Taurus to Contour, though I would definitely watch for any difference in sensor readings, when swapping them out - just in case.

thanks guys, I've already been through the intake for leaks again and again, only thing I can think of that might be leaking is the egr gasket, since I reused that one, I think it's 3 bucks, so I'll get one of those, and re-torque the back manifold and see how that works out.

I still want to think there's some kind of o2 issue though. even if there is more than one problem going on here.
 
SicSe,

You seem very knowlegable so I'm wondering if you could help with my P0420 code (lean on bank 1). Bear with me as I'm no mechanic but borrowed a friends diagnostic device and ran a test on my system and my upstream O2 is between .20 and .75 and fluxes in that range. I installed a MAF which took care of my other codes related to it but still get the 420. Haynes manual says to replace the Coolant Temp Sensor so I have that on order with Kragen now. The upstream O2 is next if the CEL doesn't extinguish. Oddly enough, the diagnostic device gives me the P1000 warning saying the evap test cannot complete. The small round icons for O2, Evap, and one other are flashing on the diagnostic computer as well. Unsure what some of this means and would appreciate some technical assistance.

James
 
thanks guys, I've already been through the intake for leaks again and again, only thing I can think of that might be leaking is the egr gasket, since I reused that one, I think it's 3 bucks, so I'll get one of those, and re-torque the back manifold and see how that works out.

I still want to think there's some kind of o2 issue though. even if there is more than one problem going on here.

hey sorry bud, didnt notice your thread until today. Just figured I would point out for you that I was throwing all the same codes as you when I had my header leak. Plus I was running pig rich. Since fixing my leak, I haven't thrown any codes
 
thanks bro, I'm leaning to the egr gasket leaking, since the exhaust hiss is only periodic, and the engine runs like except at mid throttle. I already got the gasket, but havent put it on yet because I'm in the middle of half arsed and in a hurry moving because the bank only gave me ten days to get my stuff when I was expecting 30.

if it still acts like crap after the egr gasket, I'll know I need to torque the rear manifold down again.

pm me about that quaife your selling, I could use one.

as a side note, the ' tour decided to start eating tires the week I needed it the most. front driver pitched a tread, replaced that, then the front passenger that I bought this spring litterally came apart at the side wall.

any body know the speed rating on kumho ecsta ast's? I thought they were at least v rated, but maybe I was wrong...
 
thanks bro, I'm leaning to the egr gasket leaking, since the exhaust hiss is only periodic, and the engine runs like except at mid throttle. I already got the gasket, but havent put it on yet because I'm in the middle of half arsed and in a hurry moving because the bank only gave me ten days to get my stuff when I was expecting 30.

if it still acts like crap after the egr gasket, I'll know I need to torque the rear manifold down again.

pm me about that quaife your selling, I could use one.

as a side note, the ' tour decided to start eating tires the week I needed it the most. front driver pitched a tread, replaced that, then the front passenger that I bought this spring litterally came apart at the side wall.

any body know the speed rating on kumho ecsta ast's? I thought they were at least v rated, but maybe I was wrong...

Already sold the quaife. I would think with your money troubles right now you would not want anything to do with buying parts. All I have left is a hose kit and an IMRC cover. That and the parts left on my car, but I dont feel like pulling the headers and Y-pipe, especially since I dont even have a factory exhaust to throw back on, and that just sounds like 3-4 hours of work I dont want to do.

You know.... I gotta say, you would have less EGR problems if you deleted the EGR.
 
yeah, feel ya on the egr thing, but I'm the kind of guy who'd rather spend a year doing something right than just disabling things for the sake of simplicity.

I hear ya about the money too, but heres the thing, if I dont get a helical in there, I'm going to need another 300 for a replacment case, and I wont be making any money with broke down transportation, besides the clutch is slipping and the mtx is going to have to come out again some time this winter.

in other news, got the egr gasket on today, and reset the memory, and it seems to be running better, and the only dtc I'm tripping is the p1000 so far. I drove it to griffin brothers today because a tire I have the care package on split open down the side wall on the freeway the other day and I'm rockin a steely on one wheel right now. but, being the ass that I am, I forgot it was saturday and they closed at 2, so thats on the back burner till monday.

amazingly, that tire wasnt on there long, and still had half the tread life left on it, yet the two baldies on the back have hung in there since I got the rims. also, one of the fronts pitched a tread like two days before the almost new one blew out. so I'm not having much luck lately. if griffon doesnt replace this tire for free, I'm going to go crazy.

I can't remember the speed rating on ecsta ast's, I sure hope they're not h rated... that would explain a lot. but still, the bald asx's in the back have held up fine, and they're all seasons.

but all in all, I'm just trying to get the 'tour into the best possible shape so I can go on a little extended vacation in the atl, since nobody IU know around here is doing well enough financially to take on a couch surfer while I get up first and security someplace.

sorry for the novel
 
well, it did trip the 0161 again, though it's still obviously running better than it was.

cant remember which one that is since my ford cd is broken and I was tripping so many.
 
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