I took my 91 explorer and finally got someone smart enough to run the scanner, and it threw a 41 code on the snapon tester. This says HEGO sensor lean. Where is this sensor at? Also the NEW O2 sensor I put in reads almost maxed out. This thing is running way rich. This 91 explorer 5 speed only has one O2 sensor right?

 

O2 sensor is located in the Y-pipe just in front of the cats.
'91 only has 1 O2 sensor.
Is the 41 a memory code or a KOER code or both? If that doesn't make sense, review tests at www.dalidesign.com/hbook/eectest.html You'll also see that you can pull codes yourself with nothing more than a paper clip. After you get the new sensor installed, be sure to clear the memory codes and make sure the 41 goes away.

 

I had already replaced the 02 sensor Mr. Shorty. The cats were so clogged up because the previous owner had been driving it rich like that for a long time. I replaced the cats with a straight pipe.

I have replaced:
MAF
O2 sens
Coil pack
plugs/wires
crankshaft pos sensor
reset all codes

I checked for gas in the FPR vacum tube, there was none. The new o2 sensor reading was ultra rich according to the guy who scanned it. What would happen if I unplugged it?

Thanks for the help so far, i am about to lose my mind. I dont know what else to do. Going to the gas station everyday is getting expensive.

 

So it all started with a CM (=continuous memory) 41 and it was running rich? You replaced the above items, and it's still running rich but now you have a CM 42? or do you have CM 41 still? I'm just trying to understand exactly where you stand right now.
Has anyone checked the fuel pressure? Checked for gas in the vacuum line to the fuel pressure regulator (after running the engine for a couple minutes. indicates a bad FPR)?

 

It is still showing a 141. It was 141 all along not 41 sorry. HEGO sensor. It has no gas in the vacum line on the fpr. How hard is it to check fuel pressure? I want to do it myself. I am not spending another cent at my local garages. I printed the home test with a test light.I can check the codes myself now (thanks for the link). Is the fuel pump inside the tank?

 

So it's still showing a CM 41 (that first 1 is a separator pulse separating KOEO from CM codes), and you reset the codes after replacing the O2 sensor. In contrast to the 41 code (lean), it's actually running rich. This suggests to me that you have a bad connection between the computer and the O2 sensor. It's not uncommon for wires to touch the exhaust (or other part of the engine) and melt/rub through. Basically, the second thing I did would be to trace the wires from the O2 sensor to the computer (get a wiring diagram) and make sure they are intact.
The 1st thing I would do is to run the KOER test (after warming the engine up) and see if I get a KOER 41 to go with the CM 41.

 

A bad Engine Coolant Temperature (ECT), or a problem in the ECT circuit, can cause an engine to run rich. For example, corrosion at the connection can adversely affect the ECT's "voltage drop" signal back to the PCM. The PCM, in turn, will think that the engine is colder than it really is and hence increase fuel injection pulse times to a greater degree than is warranted by the engine's true temperature.

 

Could this problem be intermitent, or once i goes does it run bad forever ?

 

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See you on the boards.

 

It could be intermittent, that's why I suggest running the KOER test, rather than diagnosing this from the CM code. If you get the same code from the KOER test (be sure to warm the engine up first or you get a false 41 from a cold O2 sensor), then the fault is reasonably reproducible, rather than some intermittent thing that comes and goes.

 

I would question the exhaust system. Did you put on a larger diameter exhaust? Your ecm could be running rich if you don't have enough back pressure.

 

I think the exhaust is the same size.

As far as it being intermittent, it does it all the time cold or warm. I ran it on the road at 3500 rpm and it was like clock work, meaning it would surge/fall every 1.5 seconds.

I unhooked the o2 sensor and went to drive it a couple miles, it would not hardly get out of its own way. I then unhooked the battery cable for 12hrs,connected the 02 sensor back up, connected battery, started it up, went for a drive and it surges really bad.
I am about to drive it off a cliff. It is the only car I have, and i cant hardly take off from a stoplight. If you floor it, it will go but it only seems like you are running on 50% of the cylinders. Thanks

 

This is a lean condition we are talking here. I think the last line of your first post confused me. As such, please disregard my previous post.

Regarding the #41 lean code and stumbling, it sounds like a fuel delivery problem to me. You really should check the fuel pressure, as mrshorty suggested. You will need a fuel pressure guage to hook up to the schrader valve located on the fuel rail on the top of the engine. Easy to do if you have the gauge. What about the fuel filter, has it ever been changed?

 

yes the fuel filter has been changed. I do not have a gauge. Are they readily available? How much pressure should I have? Thanks

 

Fuel pressure gauges should be available from any self-respecting parts house/tool shop.

Instructions for a complete fuel pressure test (including specs) can be found in any self-respecting manual (Chilton's included. see the vehicle repair guides at www.autozone.com for an online version of Chiltons).