o2 sensors...idk...

 

John:
You mentioned in earlier post that the plugs were black. All 6, or just 5? If one injector is not opening, the unburned air from that cylinder will fool the O2 sensor into thinking it's too lean - it will increase the fuel to try to get bring the exhaust O2 down, but won't be able to.
You can actually listen to the injectors click - take long screwdriver, lean the tip against the injector, and put your ear to the end of the handle (watch out for the belts and fan!).

The rapid drop in fuel pressure could indicate one injector not closing - but then you would expect only that one plug would be black. Also, you said you pinched off the line from the tank (while engine off), and the pressure did not drop. So the fuel is leaking back through the pump. Shouldn't be a problem, unless the long-ish cranking before it starts gets to be too much nuisance. (It's like 2 to 3 seconds cranking, instead of like 1/2 to 1 seconds, right?).

About O2 sensors - they need to breathe fresh air on the outside. If the outside is contaminated badly, they won't work. I had a car with a badly leaking transmission output seal, spraying tranny fluid on the outside of the O2 sensor. It didn't like it at all. I've never had one fail from being carboned up on the inside, even when I had a pressure regulator fail, putting 100-120 PSI to the injectors (perfect for making a smokescreen getaway).

The O2 sensor is like a battery. It generates voltage when there is a difference in O2 concentration between inside and outside. Rich = about 1 volt output, lean = 0 volts output. It can only make a tiny current, so any damage in the wire insulation gives a place for the voltage to short out to ground, so none makes it back to the PCM. Then the PCM think's it's lean all the time, driving it rich. In order to troubleshoot the contaminated O2 sensor problem, I connected a (digital) voltmeter to the wire from the O2 sensor at the PCM (it was easier on that car, the PCM was at the passengers feet area, with connectors I could insert the probe into. You may need to get creative to be able to get connected and still be able to safely drive.). I also have a OBD scan tool (like $35 from ebay) I've connected to a laptop computer, that lets me watch the O2 sensor signal while driving.

In summary, my suggestions:
- listen to each one of the injectors while running at idle.
- confirm all 6 plugs are black.
- check the voltage signal from the O2 sensor.

HAROLD

 

Hi Harold,

Thanks for your suggestions.

All six of the sparkplugs are evenly carbon fouled.

Just yesterday I listened to the injectors with my screwdriver (and I managed not to get myself caught in anything moving). All 6 clicked just fine and they all sounded the same to me. But I think they would click even if one or more are clogged, yes? And even if it's only a partial clog, the messed up spray pattern could be causing unburned fuel, and therefore unburned oxygen to get into the exhaust, causing the lean condition, causing the O2 to tell the computer to dump more fuel in, causing the rich condition, causing the carbon fouling and eventual death of the O2 sensor. And, I'm back to square one...

Regarding the fact that the outside of the O2 sensor can get fouled, this whole fiasco started last summer when I had a leaking power steering pump that coated the outside of the upstream O2 sensor. I THOUGHT that's what caused the original O2 sensor to fail. But that leak was corrected, and since then, I've gone through two more O2 sensors. There's nothing leaking on the outside of the current sensor, or the one that died last month.

I don't have a voltmeter and I'm a bit afraid to go poking into the wires with a voltmeter's probe (just my luck would be that I'd ruin the wire). And besides, each time the O2 has failed in the past, my mechanic did verify that the O2 voltage wasn’t happening using his voltmeter, probably in the way you recommended. Symptoms are the same again, so I’m fairly certain my present O2 sensor is dead, for whatever reason. Finding out what is killing them over and over is what I’ve GOT to do.

So here's what I'm going to do today:

I'm going to thoroughly spray clean the Throttle Body, remove and replace all 6 spark plugs and install a new upstream O2 sensor. So if the problem was the MAP sensor – fine, I’ve replaced it (day before yesterday). If it is that the plugs are too fouled from the previous O2 sensor’s failure – fine, those are getting replaced today. If the problem is a fouled up Throttle Body – fine, I’m cleaning it today.

If that doesn't fix it permanently, the next thing I'll do is to install a new Pressure Regulator / Fuel Filter assembly (the Jeep's got 177,000 miles on it and I'm sure it's the original fuel filter, so it's time to change it out anyway - and the Regulator and Filter are one unit on this vehicle).

If THAT doesn't fix it, the plan is to go after the fuel injectors - I'll either hire a shop to do an off-car cleaning and inspection of them, or I'll replace them with new ones myself ($$$$ - yech!).

And if THAT doesn't fix it, if I'm in a good mood, I'll get a full valve job done, or if I'm in a bad mood, I'll do something drastic, either involving my shotgun, or the placing of lots of Jeep parts for sale on eBay... or maybe a bit of both.

The bottom line seems to be one of two possibilities:

1) Something other than the O2 sensor is making the car run too rich (or WAS, if it was the MAP which I just replaced). Then, the overly rich condition fouls the O2 sensor to the point where it fails, causing the car to go into open-loop condition since the O2 is not reporting anything, causing the CEL to come on with the P0171 code saying a lean condition has been encountered.

2) An exhaust leak (so far none detected) or leaking valves is causing oxygen to enter the exhaust after combustion, causing the O2 sensor to read a lean condition (when there really isn’t a lean condition in the actual combustion chambers) and then the O2 sensor directs the computer to spray more and more fuel into the mixture causing in reality a hopeless rich mixture which eventually fouls out the O2 sensor until it fails and the CEL and trouble code P0171 comes up for a lean condition (due again, to a lack of signal from the O2 sensor due to its being dead at this point). I have to begrudgingly admit, that at 177,000 miles, worn out valves is a possibility – yet the Jeep uses no oil between oil changes!

Any and all help and suggestions still very much welcome!

John

 

John:
Sounds like you've got a good handle on how it's supposed to work. I haven't got too much to add (but I'll blather on a bit anyways...)
- a clogged injector could still click OK, yes. But will all 6 plugs evenly black, that reduces the probability of a single bad injector.
- a bad temperature sensor (Intake Air Temperature or Coolant Temperature) could cause the PCM to stay in Cold Enrichment mode.
- O2 sensors can be tested quite easily on the bench: hold it by the hex in a vise with the sensor up. Hook a voltmeter to the output pin and ground (the vise). Up to you to find out which pin is output. 2 are for the heater, the remaining one should be the output. If you fully envelop the sensor end in a propane blowtorch flame, the sensor should output about 1 volt. (yes, it gets red. Don't know if that much heat hurts it - I think not).
- jeeps have heated (3-wire) O2 sensors. The problem started after you replaced the first O2 sensor. Is it possible the heater circuit wiring or connector got damaged? Maybe a pin got pushed back or bent in the connector? If you kept one of the old sensors, you could cut the sensor off, and wire a light bulb to the connector, to the O2 sensor heater wires. Be careful not to accidentally short them to the Signal wire - I suspect the PCM may not like 12V going in there.
- Is the wiring and connector clean (from the previous power steering fluid leak)? I've seen it implied that the O2 sensor gets it's fresh air through the wiring harness. If that is true, then the new sensors could still be getting contaminated from the old leak.
- when I had a contaminated O2 sensor, it would seem to work for 5-10 minutes, then the voltage output would go wonky. If I recall correctly, sometimes to negative 0.6 volts, I think I also saw 1.3 volts at one point. To me the voltage readings were what finally clued me into the problem. I understand and agree with your reluctance to poke into wires. The OBD scanners on ebay are less than 20 bucks now, they can give you a lot of valuable information - I highly recommend getting one. (Far cheaper than a valve job!)
- Pressure regulator is a definite possibility. I've had one fail (high, intermittent). The PCM is not able to compensate for that much fuel.
- My opinion is that all 6 injectors spraying bad is a weak possibility. I can't see them all 6 being bad enough to make it burn so bad as to allow O2 to slip by.
- There is information on this forum (and others) about using alternate injectors (Neon, Mustang, and others). You could get a set of 6 and swap them in yourself, probably cheaper than getting yours tested. Some claim improved fuel economy, some claim increased power, YMMV. You just need to purchase new O-rings (about $15 for a set of 12)
- Get a compression check before you do a valve job, or I think you will be wasting your money. If the compression checks OK, the valves are good - certainly good enough to not cause this problem. I've got 2 jeeps, each with almost twice that many miles, engines never opened up, still going strong. Of course that doesn't mean yours is good. But worn valves shouldn't let O2 slip by either, unless they are really bad.
- If the O2 sensor wire from the sensor to the PCM is grounding out, the PCM will see lean all the time. The input impedance of the PCM should be really high - several megohms at least. With engine off, disconnect O2 sensor. Using a digital multimeter set to highest ohms range, connect black to good chassis ground, red lead to the sensor signal pin in the connector to PCM. (Measure the resistance the O2 sensor sees when it pushes it's output voltage to the PCM). It should read open circuit, or at least several megohms. Wiggle and push the wire around a bit, to make sure there is no intermittent ground.

I'll restate you two options a bit differently (actually 3):
1: The engine is lying to the PCM about it being too lean, causing the PCM to drive it really rich:
- tramp air leak
- bad O2 sensor
- bad wiring
- other reasons?

2: The PCM sees it too lean, but can't do anything about it:
- excessive fuel pressure
- leaking injector(s)
- bad coolant or intake air temperature sensors
- other reasons?

3: The PCM is bad (VERY unlikely in my opinion)

A OBD code reader will help point you in the right direction.

Good luck, I hope this helps.
HAROLD

 

Call me crazy but if I think I have an O2 sensor problem I just pull it out and clean it. Just because it dose not read right dose not mean it is bad.. The sensor can get clogged up with carbon and need to be cleaned. Pull it out and spray it with brake clean and shake it. Repeat several times and done!

 

Tried that with the first one that failed last year. Since you can't get much of anything into the actual sensor area and if you do, most solvents destroy it, I don't think cleaning them works all that well. Didn't work for me anyway.

Have you ever successfully cleaned a failed O2 sensor and brought it back to life?

 

I think it's fixed (and at this moment I'm not just knocking - I am POUNDING on wood).

If it is really fixed, I'll never know for sure which of four things I did actually fixed it, but I can live with that.

It is running absolutely perfect at this time - not the least hint of any misfiring, hesitation, black, sooty exhaust or unusually high sulfur smell from the Cat. I've put a total of about 125 miles on it since the fix and so far, it's doing well. Filled it up 25 miles back, and even after 25 miles of driving, my fuel needle has not budged one iota from the far side of the Full line. Yes!

The latest and hopefully final fixes were:

1) Installed a new MAP sensor. I actually did this several days ago and posted about it then. But at that time, I had not installed a new O2 sensor yet. So even if the old MAP sensor was bad, merely replacing it wouldn't have probably helped, as the symptoms were being caused by the failed O2 sensor (which in theory was killed by the bad MAP sensor).

2) Spray cleaned the Throttle Body. I doubt this is what fixed it, but who knows. I performed this action at the same time I did the final two things on this list.

3) Replaced the fouled spark plugs. I'm pretty sure the plugs were carbon fouled due to the O2 sensor failure, but it is possible that it was the other way around. Either way, I needed new spark plugs as the old ones were completely blackened with carbon.

4) Replaced the failed Bosch O2 sensor with a MOPAR O2 sensor. This is the interesting one! Because, I pretty much knew the symptoms were being caused by the failed O2 sensor. But what made the O2 sensor fail? And the one before it? And the one before it? etc. Well, here's my theory:

I read on another jeep forum in regard to O2 sensors that for whatever reason, Jeeps and Chryslers, and especially Jeeps with the 4.0 engine do not get along well with Bosch brand O2 sensors. Though the Bosch sensor has OEM type fittings on it, the electronics are slightly different, as the actual sensor is made to work in a variety of car brands. In particular, the resistance in the Bosch’s heating circuit is higher, which causes the Bosch brand to take longer to get up to operating temperature. There might be differences in the voltage output levels as well. Anyway, I read several different accounts of people who couldn't get Bosch brand O2 sensors to work in their Jeeps for more than a month or so. And when they installed a MOPAR O2 sensor, the problem went away.

So here's my theory, and I'm sticking to it:

Toward the end of last summer, my Power steering pump went bad, catastrophically spraying Power Steering Pump fluid all over the left side of the engine compartment, including all over the outside of the original MOPAR O2 sensor and its connection. I replaced the pump with an Autozone pump. Big mistake. Right from the get go, this "lifetime warrantee" pump leaked fluid through the main seal - and again, kept the O2 sensor coated. After about a week or two, I found the time to R and R that pump with another Autozone replacement pump (under the warranty). That 2nd Autozone pump lasted all of a week before it started leaking through its main seal. Now I was in the middle of my semester at school and didn't have time to replace it right away. After about a month or two of topping up the fluid, a bad thing happened: The Jeep started running rough, getting 9 mpg and the Check Engine light lit up. The original O2 sensor had failed. I suspected its failure was caused by the leaking Steering Fluid, and this time I took it to my pro mechanic (too busy with school and it was now winter in Chicago - I'm not a masochist). He installed a decent power steering pump (Autozone returned my money including my core charge), and my mechanic installed a replacement O2 sensor. I remember him telling me that he'd installed a Bosch brand sensor because he thought they last longer than other replacement brands. Maybe he's right about that, but in retrospect, not when the vehicle is a Jeep! Anyway, that first Bosch O2 sensor lasted about a month. Then he replaced it under warranty, and also replaced my Cat - because he thought the Cat caused that sensor to fail (now I know it was most likely the other way around).

Then, the next O2 he had installed failed about a month later and he installed another one, claiming that it wasn't the front one, but the REAR one that had failed. I find this a bit dubious, because if the rear one fails, I don't think the symptoms that had returned (the identical symptoms from every other FRONT O2 failure) would have returned. But I trusted him because he and his family's shop have always been fair with me. There have been times in the past when a problem could have been a big repair bill or a little repair bill depending on what they told me the cause was - and almost without fail, it was always the littler repair that they told me they needed to perform - so I think they are a good, honest facility. But maybe this one time, having no idea what caused the 3rd FRONT O2 sensor to fail, he had just put another one on, but told me it was the rear one to "keep me quiet". I'll never know for sure...

Well, to make a LONNNNGGGG story short, I think the problem was, that all these replacement sensors were Bosch and for whatever reason, they just don't play nice with Jeep electronics. Or maybe it was that MAP sensor. Or maybe…

The main thing I need to know is: is it really fixed, or is this latest O2 sensor also going to fail? Time will tell, and I'll report back (and I promise, it'll be a quick, easy read next time).

Best wishes, and thanks for the suggestions,

John

 

And, just a bit more than 200 miles since replacing the O2 sensor for the 4th or 5th time (lost track), the new Jeep (MOPAR) O2 sensor I installed a few days ago is failing. The CEL has come on, and the symptoms that have haunted me 3 or 4 times now in the past 7 months are back.

In trying to fix whatever is causing the O2 sensors to fail, we've:

· Replaced the Cat
· Checked for Vacuum Leaks
· Checked for exhaust leaks (see below)
· Replaced the Plugs, Wires, Cap and Rotor
· Checked for proper fuel pressure (see below)
· Replaced the MAP

Note that when I did the fuel pressure check, though the pressure when running was fine (49 lbs.), as soon as I turned it off, the pressure dropped quickly. I verified that the fuel was not leaking through the injectors (pinching off the fuel feed line kept the pressure from dropping at all, so it's not leaking through the injectors). A fast drop in fuel pressure after turning off indicates a problem with the Fuel Pressure Regulator / Fuel Filter module (slow leak would mean it's the Fuel Pump).

Do any of you think the Pressure Regulator could be causing a condition that would harm the O2 Sensor?

What seems to be happening is one of three things, either:

1. The O2 Sensor senses a supposedly lean condition (i.e. detects unburned Oxygen in the exhaust) even though the mixture is not really too lean in the actual combustion chambers and then tells the computer to enrichen the mixture (which then really makes the mixture too rich). The overly rich mixture eventually kills the O2 sensor. Basically, O2 sensor suicide. An exhaust leak before the sensor could cause this. But I can't detect one. Except: when I installed this latest sensor, I do see a tiny bit of exhaust gas seeping out from around the threads of the sensor itself. I didn't overtighten, and when I saw the bit of smoke, I tried tightening it more, to the point where I felt if I tightened it more, I might mess things up. And though I know it should not seep exhaust like this, it seems to me that since the pressure is on the inside of the pipe, any leaking would just be smoke leaking out - not oxygen leaking in. Does this make sense to you? Or:

2. One or more injectors is partially clogged and causing unburned oxygen from the affected cylinders to go down the pipe, alerting the O2 sensor to a supposed (but not real) lean situation, causing the O2 sensor to tell the computer to tell all the injectors to squirt more fuel, causing the overly rich condition which eventually kills the O2 sensor. This would be a case of fuel injector(s) murdering O2 sensors. Or:

3. Something else in the system (not the MAP since I already replaced it) is telling the fuel injectors to squirt more fuel then they should be and so despite the O2 functioning correctly, too much fuel in the mixture is causing an overly rich mixture until the O2 sensor is eventually killed (this would qualify as something - maybe the computer itself - murdering my Oxygen sensors.

Any ideas or suggestions?

What should I spend my money replacing next?!?!

John

 

Hi Harold,

I just carefully re-read your post, and now I FINALLY understand how the pressure regulator could be the cause. I couldn't understand before, because I kept thinking of it only being possibly a low pressure problem. Now I see what you mean - if it allows too much pressure, then even though the computer tries to modulate the amount of fuel, it can't.

When you say you had an “intermittent” high pressure problem, how intermittent? Were you ever able to see it actually happen on a diagnostic pressure gauge, or did you figure it out by logic and deduction?

Thanks for your help,

John

 

Soon after posting my previous entry here, I read over on jeepforum.com that Bosch brand O2 sensors don't play nice with Jeeps. It seems that even though they offer an "exact fit" replacement sensor with the correct attachments, the internal electronics are of a universal variety. In particular, their heating elements have slightly more resistance in them than the Mopar sensors do. And this leads to... having them fail every couple of months. Gee, that sounds familiar...

So I replaced the freshly failed Bosch sensor I had put in with a new Mopar one. And:

Its now been around 1,000 miles or more since I replaced the (3rd or 4th) Bosch Sensor with one from the Jeep dealer. And all seems to be well now. About 300 miles into having the new sensor, the slight misfiring, surging and Check Engine Light did come back. So again, it seemed that carbon was building up on even the new Mopar O2 sensor. ARGH! But I performed a trick I learned in another Internet discussion: To clean the carbon off, I ran the engine (in neutral) at 3,000RPM for 3 minutes to heat up the exhaust system thoroughly and burn the carbon off. This worked. The misfire and surging immediately went away, and 3 days later the Check Engine Light went off on its own.

Since then, I have done the 3,000RPM for three minutes trick one more time, but just as a precaution - there weren't any symptoms coming back. Now my wife's been driving her visiting parents all over Chicago for the past two weeks, with no problems at all.

Here's my take on why I did have the problem pop up at around the 300 mile mark even with the new Mopar sensor: Though I did reset the computer when I installed the new Mopar O2 sensor, I don't think it totally reset and it was probably still dumping too much fuel into the mixture for a while from the instructions it had received from the old Bosch O2 sensor. With time, it seems the computer has gotten its act together and maybe, just maybe, my seemingly endless O2 Sensor problem is gone.

Thanks to all who wrote replies here!

John

 

Wow painfully long and frustrating.
Just browsing rough idle threads.

But lucky me I've got a cracked head and it's the coolant in the chamber snuffing ignition.
Crappity crap

 

Yech! Sorry to hear about that. On the bright side, it's now been ages since I suffered the O2 Sensor problem and it is very clear that replacing the Aftermarket Bosch Sensor the proper Factory Sensor did the trick for me. Having had a problem since my last post, and I haven't done the High RPM trick to burn off residues since then either.

Never use anything but Factory O2 Sensors in any Jeep or Chrysler product.