You should be able to do the KOER test. Keep in mind there are 2 connectors... the trapezpoid one, and the single wire spout connector. Both need to be connected.

At this point, I assume you have replaced the plugs and wires. If so, did the engine run OK for awhile before the plugs got fouled again? One of the earlier posts mentioned the cat converter which is also a possiblity. Have you ruled that out at this point?

 

Can a CAT cause an intermittent problem such as this? I have not ruled the CAT out, as I'm not sure how to proceed with that. The KOER test will not run....could this be due to the persistant 522 code, I can't seem to clear? Tester is hooked up correctly. Plugs and wires have been changed. Engine malfunctioned shortly after plugs were changed.....and yes, wires are correctly connected. The engine initally ran ok, but next day started acting up. I don't drive the car much right now as I don't want to get stranded if I venture off too far...?

 

I am truely baffled that an engine with basically 300K miles has the original O2 sensors in it. Amazed! O2 sensors are regular maintenance items. Every 30K miles is proactive, every 50K miles is regular paranoid maintenance, every 80K is your standard OEM recommendation. So if the computer doesn't throw any codes so all must be good but then run the normal replacement items into the ground - and think, gee why does it run like crap - hell I don't know - computers are stupid?

I would get back to basics mechanically. 1 - new O2 sensors, 2 - new PVC valve, 3- new plugs/wires, 4 - clean or new MAF sensors, 5 - OK throttle position sensors.

Getting tired and out of ideas. bottom line is there is a logical cause for this and we've yet to see clerar cause/effect relationship. Keep probing and providing feedback and we'll get you running good again.

 

What are the symptoms of bad O2 sensors? I still have original sensors on my '91 an '92 with 197K and 272K miles on them. Both run great except the '92 doesn't idle perfectly as though it misses on one cylinder but not every time, if that makes sense. Would a bad O2 sensor cause this?

 

We are talking about statistics here and laws of probability. When the mean life of an O2 sensor is about 80,000 miles, and the standard deviation is let's say 10,000 miles, at your typical 6 sigma or 99.8% of the population, the highest mileage would be 110,000 miles, to have not one but two sensors make it to nearly 300,000 - it seems very unlikely. But theoretically possible. I personnaly do not believe it - but that's my opinion.

O2's fail in a variety of ways. I had one physically break and leak exhaust to the outside. This threw off the outside air reference sample and told the PCM things were lean even though all was OK. They can get contaminated say from a coolant leak into the cylinder or intake manifold. They can plain wear out over time.

I can't tell you why your car doesn't idle right. (Not enough info.) And I seriously doubt either vehicle with original O2 sensors is running at it's peak level of performance. I know from my own experience that it is not easy to remember the power my 4.0 had when it was new. Then I started to maintain it and got a bunch of power back. With slight performance decreases over time, we tend not to notice them. But it all adds up and then wow what a jolt when you maintain the car and get that power back!

I also wonder what other preventative maintenance has been lacking if you have never changed the O2's. Plugs, wires, PCV valve, cleam/replace MAF sensor, IAC valve, EGR system, air filer.... All theses things can cause a bad idle.

Now one interesting point to make on maintenance and our perceived performance level - the PCM makes corrections for failing parts over time. It adjust the A/F mix and timing to compensate for wearing parts. If it sees the O2 sensors not switching as expected, it will lean or richen the fuel tables to compensate - to a limit. Once the limit is reached and the O2 is still not switching, you get a CEL and a stored PCM code. So it is possibly, though not real probably, that your cars have been able to run OK due to the PCM intelligence even though you have some bad or ailing parts on them.

The point is, regardless of perceived condition, O2's, plugs, wires, filters...hell even tires, need to be replaced as preventative maintenance. You change the oil every 5K or so right? Same with these other, highly critical, engine control components.

I still can't belive these claims. Is it just me or do others know of cases were an O2 sensor last the life of a car?

 

Well, after I posted my question it occured to me that it is possible that some of the sensors etc could have been changed before I bought my cars. They each had just under 100,000 miles on them when I bought them used. My statement was not based upon verifiable facts. I hang my head in shame.

I have no idea what other routine maintenance items I have missed. There are so many things that go wrong with my Explorers that I only fix the things I know are wrong. I am by no means an auto mechanic. Most of the things I repair I have never done before and have to do a lot of research and get multiple sets of instructions before I begin. There is no way I'm going to take it to a professional and pay thousands of dollars for a car that may be worth only a couple of thousand dollars. But I try to keep them in good condition and do the things I know about. Nearly all of the information I get, aside from step-by-step instructions from my Hayne's manual, comes from the internet. But I cannot ask a question that I don't know to ask. Fortunately there are people like you who share information with people like me so cars like mine are still running (197,000 and 272,000 miles on '91 and '92). I suspect something is amis because neither seems to have quite the power it should but since the CEL doesn't say something is wrong I don't know to look. OTOH if the temp gauge reads high or the battery gauge reads too low I can grasp that there is an immediate problem and so far have always managed to solve it. Both trucks always easily pass the smog test here in California so based upon that they must be running fairly well. I keep good tires on them (Michelin LTX M/S) and make sure the brakes work properly but I do not change my oil or air filters very regularly. It's kinda amazing that they still run, huh? I live on a dirt road so the air filter gets dirty very quickly. I take it out and shake it off once-in-a-while. I make sure things like the serpentine belt isn't about to snap and the radiator hoses aren't about to burst and buy only the best batteries and keep the connections clean. I replace spark plugs and wires and PCV valves and radiator caps etc. as needed. I try to avoid repairs with duct tape and bailing wire. I spend so much per month on auto parts that I could just about make a car payment on a new car but I'm afraid whatever it is may not be as capable as the old Exploders and I'll end up stuck in the mud somewhere. I just bought a '97 Explorer with Control Trac and I have doubts about it's abilities because of the drastic changes on the chassis and suspension. But it's a very good looking 4X4 in very nice condition and I got it for a great price. I'm going to research it now. Say, do you happen to know where the remote entry module would be located, if it has one? It didn't come with remotes but it's an LTX. No sunroof either so maybe it was a package. I know where it goes on the '92....

BTW both (now all 3) of my Explorers actually LOOK nice except for a recent event where one got stuck in a rut and they banged into each other while being pulled out but the damage was very minor. A lesser vehicle might have been severely smashed in the same circumstances. I am working to restore them to their previous condition.

In case it's not clear I really appreciate your help and advice.

 

And what's wrong with duct tape and bailing wire? Go to this web site and learn all about Ford EFI systems. Great site http://www.fordfuelinjection.com/

I learned much of my knowledge on controls systems there. It's not too complicated and once you understand it, it makes a lot of sense and troubleshooting becomes a breeze. But all the items I mentioned above are all inputs or outputs from the computer and all affect how it runs.

Hey - you CEL migh not even be working. Does it flash on when you start the car? If not, he bulb is burned out and you might have a dozens codes stored and never know it. Just check you codes anyway. I do every couple months. You may get codes and never have a CEL flash too.

I don't know much details of the later model trucks. I bought my 1993 new and never liked what Ford did in later years. rack/pinion, independent rear and they look like minivans - in my opinion.

Last thing - study your electrical schematics. Understand what controls components you have, how they are hooked together. in conjunction with the EFI web page, you'll never need to go to a mechanic again.

 

And then when you are all done understanding how it is supposed to work, go to this web site and see how to fix it. Not everything but the typical Explorer issues and fixes are listed here. http://draco.acs.uci.edu/explorer/
last week I used info found here to replace my driver's side door hinge pins/bushings. For $11, my door doesn't sag and it closes almost effortless.

 

Thanks for the link.

This system sure loses a lot of words and crams other words together. Kinda makes it hard to read when you have to guess what was written.

 

Just a short note to update those interested. Jharger shamed me into changing my O2 sensors out. Unfortunately, the auto was running ok at the time so no confirmation of positive fix. To date, O2 sensors, plugs, wires, pcv have been changed. I "think" car is running better with the new sensors, but time will tell. PS for Jharger, in checking my owner's manual, and in my defense, it never had me check or replace my O2 sensors throughout the 120K mile schedule. I followed my scheduled mx pretty faithfully for the first 6 years or so. Honestly, with 294K miles on this engine, everything is gravy from here. Don't know if the Mobil 1 that I ran in it at 15K intervals had anything to do with it or not, and I don't want to open up another bucket of worms, but am so impressed with this engine, just hope my 2004 F150 goes as far.
I'll report back to forum if/when this problem recurrs. Thanks for everyone's input.

 

I too reread all the scheduled maintenance but in my Hayne's manual instead of the owner's manual and it didn't say anything about periodically changing sensors and such. I do all of the recommended maintenance just not at specific intervals but more on an as needed basis. The Hayne's chapter on emissions control system explains what all the sensors do but it sounds like special equipment is needed to test them. Meanwhile I took my '92 with 272K miles on it to get a smog test yesteday and it passed the "enhanced" test easily. The engine runs very close to great. I am attributing it's current remarkable condition to JB Stop Leak. This may be a half-assed way to fix a car but it seems to be at least postponing pulling the heads and replacing the gaskets or whatever other horrible things are lurking down there. Some day I'll get around to fiddling with 02 sensors and such but now I need to find out where all the "clunks" are coming from before it gets to the point of causing roadside adventures.

 

Mr Dblee540 - I'm sorry to have shamed you into performing a maintenance task on your vehicle. My post were to merely show the typical performance of components. It is rare for an O2 sensor to work as design past 100K miles. Your mileage numbers were staggering. So one must first question the reliability of the data provide. Sorry, this is basic science. I do not think any reputiable mechanical would question and not even suggest to not change an O2 sensor with <80Kmiles - just beacause.

As far as the owners manual - you will never see it tell you to change a polution control device on a regular schedule. The auto companies have strong lobbies. This is something you need to take from us your a "good" mechanic if you want your rig to run correctly.

There is no doubt in any self schooled backyard mechanic or any ASE certified and trained mechanic or a mastered degreed engineer as myself, that the O2 sensor is intentionally desinged to be regularly changed maintenance device!

 

OK, you got me thinking about my 02 sensors but they way I'm looking at it right now is that I have no way of determining if they are in any way defective. I would have to spend about $80 to find out. My montly allowance for my '92 in only $15 and I already spent over $200 on it this month ;-) It is semi-retired (don't want to push our luck) and my wife mainly just drives it down the dirt roads when it's raining. The engine runs quite well considering how many miles it has on it. From the driver's seat I can see a $200 repair bill staring me in the face in the form of a cracked windshield. For me that is a priority but you have convinced me of the need to replace the 02 sensors, just not this month. I just bought a '97 Explorer with the same 4.0 EFI engine as my '91 and '92 and it seems to be a LOT peppier. In my Hayne's manual it attributes lack of engine power to, basically, either a clogged fuel filter or inadequate spark. It also mentions brakes dragging but I do my own brakes so I know that's not the problem. The Hayne's manual also mentions that according to Ford the fuel filter should last the life of the engine. It does not, however, say how long that life expectency is. Since they made the odometer only go up to 99999.9 I guess that narrows it down. I would expect that if the fuel filter was clogged the engine would not run very well or be able to accelerate without great difficulty. Is there some way to test the ignition module to determine if the spark is weak but still consistant? The other low power possibililty that Hayne's points out is low, uneven cylinder compression. Well, at 272,000 miles that would probably mean a rebuild so I'll focus on the other two possibilites for now. The fuel filter was changed on this Explorer about 100,000 miles ago. Would you recommend changing it again? What else can I do to try to restore power?

 

Dblee50 - you say "O2 sensors, plugs, wires, pcv have been changed." Did you disconnect the battery right away before starting to drive it again? This not only resets the computer codes but it rests the computer back to a facotr of "1" for all the correction factors it learns over time. If a O2 sensor was off a little and the PCM was compensating for that, it might now be double compensating. So it really depends how far you've driven becasue after about 100 miles, the PCM will be all relearned anyway. It will eventullay get up to its full power potential but if you reset it whne you make any major changes like this, you can notice the difference in performance immediately.

I didn'y msee amywhere where we talked about the IAC or MAF sensor. The IAC valve controls idle. If you had a rough engine only at idle, the IAC could very well be the culprit. These can be disassembled and cleaned - but sometimes still need to be replaced. The more I think about it, the more I think this could be your issue. IAC's can cause intermittent idle problems. They have no feedback to the PCM so manytimes you don't get a code. And for OBD1 EEC-IV set ups like you and I have, there is no code that says bad IAC. You might get a low RPM at idle type code but no ****, the tach is telling you that already. And then you still need to figure out why the idle is low - hence here we are. Try to remove it - looks like a silver canister on the top of the intake manifold. It only has 2 wires going to the connector. Since your problem is intermittent, you may not know right away if it's fixed but if it keeps recurring, I'd go ahead and swap it out.

On the MAF sensor - this will be another one like the O2's. Regular maintence is required even though catastropic failure has not occured. Check this link to find the thread on cleaning the MAF sensor - under "engine pinging". http://draco.acs.uci.edu/explorer/

Typically a real dirty MAF will run your motor lean and you get severe pinging, especially up hil. This drove me nuts for a couple years before I found the above web link. I suggest you do this even if you do not have pinging since it is likely you are still running a little lean and are cutting back on your power somewhat.

And as I mentioned before, disconnect the battery for 10 minutes to reset the PCM after you do either of these.

 

therealulysses - I know what it's like to be on a budget. I don't know of a good way to clean O2 sensors. The PCM can compensate for them a little so it might be OK but eventually performance will start to suffer.

As far as power loss, the repair manuals talk of generic situations that apply to all cars. While these things are all true, we are talking in this thread about a major loss of power due to specific and known reactions of the EEC-IV engine controls system. I would worry about a dragging brake caliper unless you have inspected it and found it to be stuck. Not a typical problem for Explorers.

Fuel filters certainly can get clogged. In the old days, cahnging them was part of any tune up. The ones in all you Explorers are meant to be lifetime filters. Well if you drive as much as Dblee50, a lifetime could be pretty long. I changed mine out twice in the 170K miles I have but I'm just paranoid. Last time was about 70K miles ago. There is alos a filter on the pump unit in the tank. This can only be changed by dropping the tank. The one under the drivers seat in the frame rail (behind a metal bracket) needs special tools to break the line apart. Autozone has them for sale or borry.

I think you older Explorers are suffering from basic lack of maintenace. Plugs, wires, MAF sensor cleaning, O2's, air filter, maybe fuel filter, maybe IAC cleaning... If you get through all this and reset the computer, you should notice some improvements.

If your 97 is a SOHC motor, it has more HP than the standard 4.0 anyway so maybe that's part of the difference you see.

And as you mention, with so many miles, a major mechanical issue may be present. May need valve job, may have cracked heads...