The check engine light has been coming on ever sense I purchased this my 92 XLT 4.0L I took it in to Autozone and had the error codes read a while back and got a running rich on the left bank code. The previous owner had recently replaced the O2 sensor so I assumed that was not it. Instead I put in a new set of plugs and wires and cleaned the MAF sensor thinking that would solve the problem. Well it did not.

I have been driving the truck now for nearly a year now. The light only comes on once the engine is warm and then stays on most of the time though it will occasionally switch off. There is absolutely no noticeable performance problems, the engine runs smooth and has plenty of power. Well, that light gets pretty annoying so I took it back and hooked the diagnostic tool up. It had the following codes stored:

0172: "The O2 sensor is sending a very low signal all the time, that means the fuel system is fixed lean or there is a problem with the O2 sensor"

0193: "The O2 sensor is sending a very high signal all of the time. This means that the fuel system is fixed rich, or there is a problem with the O2 sensor"

0543: "indicates that the ECM is energizing the fuel pump relay but the pump is not running during vehicle operation or key on a hard start cycle"

0211: "the profile ignition pickup signal was erratic or out of limits for a short time on an intermittent basis during vehicle operation"

Any ideas what the combination of these codes mean? I don't see how an engine running as good as this one is can have so many stored codes. I am thinking about resetting the ECM, driving until the light comes on again and then have them read. Hopefully that will tell me which one is causing the light to come on first, and the others are just a result of that system failure.

My instinct tells me that something is up with the O2 sensor sense it is giving high and low readings consistently and sense the light only comes on once the engine is warm and thus running closed loop. Is there more than one O2 sensor on these engines? Otherwise how would the error code know which side was running rich?

Thanks in advance for any help provided

 

I'm preaty sure I've read on this site that the 4.0 has three O2 sensors. One on each sde and one just after the converter I think. It seems to me that if one up front was bad and reading lean alll the time (making the enfine run rich) it would cause the other to read rich. I think you should first pick up a haynes manual, and second, either brake down and buy your own code reader ($30 at autozone) or do it the manual way described in the haynes. You can then clear the codes and do an engine running test. I don't know this, but it seems that the one bad O2 sensor could be the cause of most of those codes.

Hope this helped

 

Do you ever have any black smoke from the exhaust, any gas in the oil, any vacuum leaks, any exhaust leaks, is the PCV system working good, is the fuel pressure within specification and constant, do you have gas in the fuel pressure regulators vacuum line? The 4.0 can have vacuum leaks around the fuel rail upper intake.

There are three different types of codes and they should be addressed in a specific order. When you had them pull the codes did they say which type they were? Did thet run the key on engine off test and/or the key on engine running test? You can pull the codes/run the tests without a scanner by using a jumper wire and the CEL.

You have at least 2 O2 sensors, one for each bank and possibly a third one which only monitors the cat and does nothing for mixture.

Sorry for all the questions but this is a tricky problem.

 

No, never any black smoke at all, truck appears to burn nice and clean, no gas in the oil, no vacuum leaks that I am aware of, however, I will take a close look at this as I had not considered it being the cause. I assume the fuel in the fuel regulator vacuum line would indicate the regulator has blown a diaphragm?

I have to admit I do not have a manual, and I am actually selling this truck to move up to a full size for towing the new boat so I would like to avoid purchasing one. So, can somebody tell me where I should attach a fuel gage, and what the pressure at that location should be?

Autozone did not tell me what type of codes they were (two employees had trouble counting them the blinks because they were looking for two digit codes, not three). However, the test was done with the engine off, key in the "on" position.

I need to crawl under the truck and have a look at the O2 sensors, I only recall seeing one last time I was under there, but that is all I expected to see (can't remember if it was before or after the cat). I am wondering if the previous owner only replaced the one sensor.

I will do some investigating around the truck when I get home from work. Thanks for the tips, no problem in terms of asking me questions, if we can get to the bottom of this it would be a tremendous help.

 

You are correct about the diaphragm.

Attach the fuel pressure gauge to the valve on the fuel rail and it should be around 35-40psi, I don't have my specs with me.

The key on engine running test is an important test. The test that they ran will give you KOEO codes and continuous codes. You should address the codes in this order, KOEO, KOER and then continuous. You really can't say for sure which type they got so it might not be a bad idea to run them your self.

 

I don't get time to work on the truck much, but here is the latest news....

When autozone pulled the codes for me they printed a list of pin-point tests. I spent several hours completing most of them, looked for vacuum leaks, checked electrical system, and some of the fuel system.

Well, everything seamed to be checking out, and I got to thinking, most the other codes were probably triggered wile I worked on the truck, I disconnected the fuel pump fuse one time when the truck got flooded (triggered the 543), had just put a new set of wires on the truck and had one loose connection at first so that may have triggered the 211. I thought "what the heck" sprayed some CONTACT CLEANER on the O2 sensor connector, cleared the codes and drove back to autozone hoping to only get the root problem codes.

Well, on the drive the check engine light only flashed briefly for less than a second, (half hour drive). Usually it comes on as soon as the engine is warm and stays on. The only code returned was 173 - or the rich code, same one I got the very first time I pulled the codes.

Thus, I though, geeze, it has been the O2 sensor connector this hole time, just dirty. Sense the light did come on once I opted to take it apart again and clean it up really good. Well, after that, the light is back on all the time.

Would clearing the codes make the light stay out that long? Or is there really a problem with the O2 sensor connector?

Also to my surprise, even though I am told the truck should have two O2 sensors, it only appears to have one, just after the left and right banks go through a collector.... anybody else have this?

Finally, is there any good way to look for vacuum leaks other then visual? I looked for cracks in the vacume lines and listen for leaks, however, it seams so easy to miss the various gasket leaks (like the intake and vacuum diaphram valves).

 

Clearing the codes would only turn off the CEL until the error happened again.

I use carb cleaner to check for vacuum leaks, the idle speed changes when the leak is blocked. Do this with a cool engine since the cleaner is flamable.

Did you try running the pinpoint tests for the O2 to see if you can figure out what connection is bad, it might be the wire and not the connector.

 

92 models DO NOT HAVE downstream ego sensors . They are only on the 96 and up OBD2 models. My guess is bad MAF sensor and possibly the TWO ego sensors are contaminated.

 

That truck only has 1 or 2 O2 sensors. No post catalyst sensor.

It does sound as if there is one sensor bad.