I'm kind of a little astonished.

Cut to the last paragraph if you don't want to read the novel I've written. :laugh:

So for the better part of 1.5 years my 2001 has have seven malfunction codes. I'm not motivated enough to fix everything in one swoop, so over the past few months I've rebuilt my NSS and sorted out my AUX fan circuit problem. That was two codes taken care of.

Three days ago I was underneath taking my broken front driveshaft out and was messing with the half inch round plastic line that runs along the driver side unibody rail. I was pushing it back into it's clips when I also noticed what looked to be a steel line that runs right with it. I was pushing on that, and noticed it seemed to move around way too freely for something that came from the engine bay. So I climb out from under the XJ...pop the hood...and start to look for it.

Sure enough, it wasn't connected to what appeared to be it's only possible receptacle. I plugged it in and trace where it went to in the engine bay. To my surprise the tag on the line says "EVAP." The Evap code has been something I couldn't figure out for the life of me for the last 16 months.

I then bring it over to Advanced Auto and have them scan the codes. Five came up, like I expected. Two for a cylinder misfire, two for catalytic converters/O2 sensors, and the Evap. He cleared the codes for me...and they haven't come back yet. I've even put over 100 miles on it just to see if it would come back on.

So, I guess what I'm trying to build up to here, would an Evap line cause catalytic converter/O2 sensor codes to be thrown? Let alone a cylinder misfire? I'm not holding my breath on the misfire one though. I'm sure that one will bite me in the ass again.

Anything is possible, but its not likely

Spend 50 on ebay and buy yourself a decent scan tool. You'll save that in gas going to the parts store to have them check codes.

Pen_Two said:

So, I guess what I'm trying to build up to here, would an Evap line cause catalytic converter/O2 sensor codes to be thrown?

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The codes may or may not be related.

What can happen, is that a bad sensor or a failed part will cause the engine to run too rich/too lean, or to misfire. The ECU is not smart enough to add 2+2 and get 4. It sees a bad sensor in one location and an out of tolerance sensor reading in another location, and gives the trouble codes for both "problems". Fixing the sensor and/or the lean/rich/misfire conditions, clears the original code and the other (related ?) codes clear up as well.

Your fuel return line (what I think was unplugged) was disconnected?! You should see your gas mileage improve a bit soon. Unless there are four lines on that frame rail on the 2001, that's the only thing it can be, because the other two are rear brake (you would notice this!) and fuel supply (you would also notice this). As Tim said, the ECU isn't that smart - I'd suspect what happened was the evap error made it drop into rich mode, which resulted in the O2 sensor code and possibly the misfire. The misfire could also be from a long time ago when your spark plugs needed replacement or something, and just never got cleared - that is, if the ECU keeps records of errors from previous runs, I'm not sure if it does.

kastein said:

Your fuel return line (what I think was unplugged) was disconnected?! You should see your gas mileage improve a bit soon. Unless there are four lines on that frame rail on the 2001, that's the only thing it can be, because the other two are rear brake (you would notice this!) and fuel supply (you would also notice this). As Tim said, the ECU isn't that smart - I'd suspect what happened was the evap error made it drop into rich mode, which resulted in the O2 sensor code and possibly the misfire. The misfire could also be from a long time ago when your spark plugs needed replacement or something, and just never got cleared - that is, if the ECU keeps records of errors from previous runs, I'm not sure if it does.

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97+ does not have a fuel return line, the fuel pressure regulator is in the tank. This is an evap line that is used to burn vapors from fuel tank.

goodburbon said:

97+ does not have a fuel return line, the fuel pressure regulator is in the tank. This is an evap line that is used to burn vapors from fuel tank.

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Ah, my mistake! Sorry to mislead.