Oxygen sensor bad?

[1RadCJ5]

Just looking for opinions before I replace the oxygen sensor in my 92 explorer sport, 4.0.I all of a sudden got a check engine light after about 10 mins of driving.The light stays on until I shut the key off.After a few more mins of driving, it will come back on again.I noticed that my idle is a bit erratic, and the exhaust smells very heavy, like it has too much fuel all of a sudden.I went to the local autozone, and used a code reader on it.I got 2 codes, a 172 and 173, which according to the haynes manual is a lean oxygen sensor and a rich oxygen sensor.I obviously think its the sensor.I have a friend that works at ford, and he seems to think it may be something else, its just the sensor picking up the problem.I have driven this truck for 4 yrs and never replaced it, and who knows if or when it was done before I owned it.Would I be doing the right thing by just replacing it? I looked for any loose vacuum hoses, etc. but found nothing.The truck runs ok, and is still pretty peppy, its just an erratic idle, alot of stinky exhaust emissions, and Im sure i'll see a decrease in gas mileage.Any info is very appreciated.BTW the truck has 160,000 miles, and ran like a top before this. Thanks again! Mike

 

[JDraper]

Welcome to the board!!


I'd agree with the mechanic. Sounds like the 02 sensor picking up something else going wrong, like a bad fuel pressure regulator, stuck injector, or Mass Air Flow sensor acting up.

You may want to spend some time diagnosing before you start throwing parts at it.

 

[ma96782]

You got a "friend" who works at FORD.....what a great resource.....why not listen, learn? Or you don't ,"trust his analysis?"

As for code 172/173......

172 System too rich Bank 1
173 Fuel trim malfunction

At any rate SEARCH.......will give you alot of leads.

Aloha, Mark

 

[1RadCJ5]

Yes guys, I have a very good friend who works in a ford garage here, and has for many years.Normally, I would just have him fix it, but he has a lot of things going on right now, and he just cant help me right now.I have definately reconsidered changing the oxygen sensor.I read in another posting somewhere here that another guy had the exact same problem, and it turned out to be the fuel pressure regulator.I guess I have to locate or buy a guage for it to be tested.I have the mechanical knowledge to replace it, but I'd like to be sure, or at least pretty sure before I just hit it with new parts.Like I said earlier, it is as peppy as it ever was, it just idles a bit rough, and the exhaust smells very rich...Any other input is appreciated, thanks so much guys for taking time out of your thanksgiving to lend me some advice.When I figure this out, I'll report back, and maybe help someone else down the line. Mike

 

[ma96782]

Yes, I've heard that a replacement of the FPR has done it in some cases......but, since you don't like to just throw parts at it (neither do I).....then you'll need to test the fuel pressure.....to KNOW.

Aloha, Mark

 

[1RadCJ5]

Well, Here I am with more info, if anyone is interested.My friend came by with his ford-borrowed scan tool, and fuel pressure guage.The fuel psi was very good he said, and it looked good to me.I think I had around 40 psi with the engine running, and around the same when keying it on to prime the pump.I could be off a bit, but it was around there.The O2 sensor was pretty inactive, and he felt there was good reason the replace the sensor.I replaced it today with a brand new oem sensor.It idled better right away, but after 10 mins the light came back on.I then figured I'd try cleaning the battery terminals in prep for winter, and keep em off for about 20-30 mins to maybe reset the ecu.The light still comes on after awhile, but then went out after a few mins on the pike.On the way home it stayed on the whole 20 min trip, once it came on.It did buck n kick today when it w as cold at a stop sign.I had hoped the sensor would have cured it all, although it absolutely does run better.Im gonna try to test or clean the MAF sensor tomorrow, nothing to lose.Sorry Im long winded, just trying to be informative. Mike

 

[glfredrick]

I'd suggest that the O2 sensor is doing just what it should do -- read and report a bad reading.

Something else is most likely causing the problem. I'd check the intake system. Air filter, MAF, clean out the intake, change the plugs, new wires, etc. By chance, did you install something like a new air filter or intake system? Over-oil a K&N and you get similar problems as the oil kills the MAF.

 

[1RadCJ5]

I have to agree, I think the O2 sensor is just reporting the problem.I just came in from looking at it a bit.The air filter is squeaky clean, MAF seems to be ok, the little resistor thingies look intact, and are clean.Nothing new has been installed, and it has no K&N in it.I dunno why the check engine light went out after awhile last night.I guess its still a mystery to be solved.Worst case, the dealer can mess with it, but then it'll cost a fortune.My ford mechanic friends 15yo son is having heart surgery tomorrow, so that is why I'm not asking him for help, he has MUCH bigger issues.I'll eventually get it.Any other info is greatly appreciated.Thanks everyone! Mike

I'd suggest that the O2 sensor is doing just what it should do -- read and report a bad reading.

Something else is most likely causing the problem. I'd check the intake system. Air filter, MAF, clean out the intake, change the plugs, new wires, etc. By chance, did you install something like a new air filter or intake system? Over-oil a K&N and you get similar problems as the oil kills the MAF.

 

[sumless]

Hi All,

1994 Explorer, 170k.
I'm having the same issue as 1RadCJ5. Codes 172, 173, and rich smelling. I've done the following to try and fix the issue:
Replaced Fuel Pressure regulator, Replaced MAF, Replaced SparkPlugs and Wires, replace both O2 sensors, and replaced the throttle position sensor, all to no avail. One thing of interest is that upon cold startup, runs fine and smooth. It takes several minutes for the Check engine light to come on, once warm just off idle (pressing down maybe a touch to raise RPMs to 1500-2000) it bogs (misses but not consistantly as with taking off a sparkplug wire where theres a destinct rythym there is none). Keeping the RPMs (in park) about 2500-up is fine, like theres a flat spot off idle. When I unhooked the TPS, this problem goes away, but obviously Checklite is on and the Trans won't shift or Lock the converter while driving, so thus I replaced the TPS, no dice. Same problem.
I was suspecting an injector, but what holds me back from that is the fact that cold, it runs great, and without TPS signal it runs great. Does anyone know if maybe the Coolant Temp Sensor might be causing this?
Only other thing I can think of is maybe the EGR Valve is messed up?
What other things might be dropped in limp mode (no TPS signal, computer runs factory defaults).

Thanks In Advance!!!!
-Joe

 

[Positive Vibes]

You guys try and change the PCV or IAC???

 

[1RadCJ5]

I havent replaced either of those, but it's been parked for awhile.I do wantt o fix it though.I did check the pcv valve, and it rattled freely, so I didn't replace it.I never tried unhooking the TPS sensor, but maybe I should, just for the information on whether it runs better or not.I actually was suspecting the EGR valve, but I can't even see the damn thing.I do know that I started the truck the other day, and in the snow it left LOTS of soot, and black.Definately really rich.Keep posting info, maybe if one of us figures it out, it'll help us all! Mike

 

[sumless]

Thanks for the response Positive.

Yeah, been keeping up good with the maintenance on it. When I got it had 120k, I replaced PCV, Fuel filter, cleaned out the EGR, nu Airfilter. Tried high octane, injector cleaners but nada. I'll not mention all of the U-joint replacement since I seriously doubt those play a part in this.
1Rad, I will mention that the sooting seems to have stopped, still present if it idles for a fair amount of time, but always smells rich at idle. The EGR on mine is on the driver's side upper intake, a 3/4"(aprx) pipe feeds it from exaust below on the driver's side.

At one point I thought maybe the Catylatic might be the culprit, since it always seemed lacking in flow on the exaust, so I cut a hole before the cat, about 2inches by 1. Sounded more healthy, but no changes. Ended up welding that back up. A bit too noisy.
Only thing I am perplexed on is the disconnecting the TPS, and Why is it 172,173, (Right side specific) I would think I should see 176, 177 (Left side),
However looking through the Code book, 172&173 are Continous and running, 176 & 177 are only Continous. Hmmm. Maybe the 172s and 173 are rolling over them. Dunno.

The IAC was another thing I checked out. I disconnected that, obvious idle drop and stumble while hot, stall while cold. I took it out tested it and it checks out fine.

Very puzzling. On the off chance it was a single injector, I've done the Cylinder Balance test, didn't see any particular issue.
Only other item, and wondering if 1Rad may have simuliar, there was a remote start system on the truck when I got it, didn't seem to work, but noted a mysterious wire (looks like a tach feed so the system knows its running?) that abruptly ends, from the interior, not a factory unit. But that may only confuse the issue.
Well hopefully with all this snow on the way (here in NewEngland expecting 6-12" tonight tomorrow) it'll just be a nuisance.
Cheers,
-Joe

 

[Positive Vibes]

Have you guys tried to sea foam the engine???

 

[mikeinri]

I had similar problems a few years back. I was getting the CEL, then got lots of soot. Took it to a Ford dealer, they replaced both O2 sensors, plus the MAF sensor. They then cleaned the intake (you could do this with Sea Foam).

The problem went away and has never returned in about 200,000 miles.

Not sure that your problem is identical, but it could be related.

Normally, if any of the other components you mentioned are bad, you get a CEL specific to them, including the temperature sensor. (I also had that problem once, couldn't believe how badly the truck ran from a bad temperature sensor.)

I've also had EGR issues, with CEL, but they didn't really affect the way the truck ran, and certainly didn't cause soot.

One other thing that has caused issues for me is vaccuum lines blown off the tree (sometimes caused be a bad tranny modulator), and leaking vaccuum connectors. Double check those, they don't always cause CEL, but definitely will make the truck run like garbage. You could have a disconnected vaccuum line, or a brittle (leaking) connector.

I'm guessing here, but if you ran it that way long enough, the computer might try to compensate for that by adjusting other parameters, and those changes could eventually cause the O2 CEL.

Joe (sumless), you might look into the tranny modulator, or other vaccuum leak. The tranny needs vaccuum to shift correctly. (Edit: I just noticed, are you only having tranny problems with the TPS disconnected?)

Hope this helps.

Mike

 

[Pollarican]

I had the same symptoms as you guys about half a year ago - Check engine light going on and off (with the same code), rough idle, rich fumes, and worst of all terrible milage. I replaced fuel filter, oxygen sensor, fuel pump, ect. and it was still running very rich. In the end it was the Fuel Pressure Regulator, and my reccomendation would be to get your fuel pressure checked as soon as you can. At one point, I was getting like 130 miles on a tank haha.

Another thing you might want to look into is replacing your fuel pump relay. Pretty cheap at around 15 bucks, and I could hear that my fuel pump would whine for a few minutes after my car shut off before I replaced the relay. Hope this helps, I'm pretty confident in the FPR being the culprit - It seems to have happened to several people on the forum with first gen Explorers.

 

[1RadCJ5]

I did have a buddy check my fuel pressure.He pretty much ruled out the FPR.Had very good pressure both when I turned the key on,and running.Also had good pressure under a load.All my hoses look good, no leaks detected.I did replace the O2 sensor awhile back, no help.I am thinking of taking it in to a mechanic, but know they may just throw parts at it.I can do that myself! My temp guage is all over the place, seems like a common problem on these.Its been that way forever though, with no probs, so I doubt it's the cause of my CEL and crappy mileage. Its a pain in the a**.Well, hope this info is somewhat helpful, I'm on my way out to snowblow all this fresh Maine snow, fun fun! Thanks for all the input guys! Mike

 

[MrShorty]

1RadCJ5: In all the replacing of parts, have you carefully inspected the wiring between the right O2 sensor and the computer? It's not unheard of for wires to contact exhaust manifolds and melt through or, if the transmission has ever been removed, to get pinced between the bellhousing and the engine.

Do you have access to a good scanner? I think it would be real useful at this point to "read the computer's mind" to see what it is seeing.

O2 sensor signal is 0-1 V. Because the signal is so small, it's possible for a fault in the computer's grounds to throw off the measuring of the O2 signal enough to cause problems. Only takes a minute to measure the voltage drop across those grounds and make sure they are good.

I also wouldn't completely rule out a bad computer. One of the toughest diagnoses I ever did was on my old Chevy with an O2 sensor code. Turned out to be a fault in the computer itself. The reason diagnosing a bad computer is difficult is because you diagnose the computer to be bad by process of elimination. If all other possible causes have been eliminated, then the computer is at fault. Of course, it's a pretty tall order to eliminate all other possible causes. (I ended up paying someone to diagnose this one for me).

Diagnosing O2 sensor codes can be among the most difficult codes to diagnose. If you lack the tools and skills, it might just be worth paying someone competent a diagnostic fee to get to the root of the problem.

 

[mikeinri]

Reading these last few posts brings a few things to mind.

The temp sensor for the computer is a different part than the one that sends the signal to the dash gauge. Not saying that's your problem, just wanted to make you aware that they are definitely not the same part, so a waving dash gauge would not cause a computer code, or vice-cersa. The only time they could both give bad readings at the same time is if you really had temperature issues (or lost a bet with Murphy).

Mr Shorty brings up excellent points, and reminds me that the best "accidental" troubleshooting experience I ever had was at an AutoZone a few years ago. They read my codes, then entered them into their computer. It printed out (on a fairly long register tape) a very detailed troubleshooting procedure for the code. In my case, it was the MAF sensor. The procedure was extremely detailed, down to telling you how much voltage or resistance you should get on a particular colored wire in the harness, etc.

Of course, not all the stores are so helpful. Some won't read the codes for Gen 1 Explorers (only have scanners for the newer cars). At the store I went to for the MAF, I had to leave and come back on a Saturday morning, because they only had one guy who knew how to use the reader.

But my point is, if you know the codes, you may be able to check with AutoZone to get a more detailed troubleshooting procedure.

Admittedly, O2 failures suck, because they're at the tail end of a long chain of items that could really be the problem, so you may end up at a mechanic anyway, but it's always good to go in with as much knowledge as you can get!

Good luck, keep us posted.

Mike

 

[sumless]

Hey Mr.Shorty, Mike, and Pollarican,
Thanks very much for the pointers. I've pretty much ruled out and issues with regard to the O2 sensor and the connections. I'm wondering if this might indeed be a computer problem. Luckly, I've aquired another Explorer, long story short, I picked it up for 200bucks. Figure I can salvage the Computer out of that and swap it with my own. Couple of questions for ya guys, 1. Is there anything special about swaping out the computer module, asside from the obvious (disconnect battery). 2. Are all of the computer modules within this year pretty much the same?(i.e. firmware versions) and 3. after all of this, i.e. rich running, are there some other things I should do (change Catylatic) as fall out from the poor running?

Thanks Much!
-Joe

 

[sumless]

FYI, here's what I got for 200bucks. Looks mostly cosmetic, no frame damage so. Almost wondering if I shouldn't rebuild it, since its condition is as good or better than my current Explorer.
http://www.sumless.net/ex/index.html

Tomorrow the computer swap, but kindda holding out to see if theres any advise you guys have about swapping the computer module. Give me a router or firewall, not a problem, but the computer in my Explorer, I can't get a replacement for free...

Cheers!
-Joe