Good afternoon gentlemen. I am new to the forum, so naturally I have a question.

I will start at the beginning.

I have a 2005 5.7L with about 72K on the odometer. The truck is completely stock as I am going for longevity and fuel mileage rather than performance.

I started with a code 305 cylinder number five misfire as well as a p0300 random cylinder misfire in addition to rough starting and bad idle on initial start-up.

I changed plugs, wires, and PCV as part of the 60K service at 70K.

After noting that I had no fuel pressure when the truck sat overnight, I narrowed the misfire down to a bad #5 injector.

Changing the injector cleared up the misfire codes.

Several days later, a P0420 bank 1 catalyst efficiency code popped up. My working theory is that the liquid fuel that was sitting in #5 destroyed the cat before I fixed the problem.

Now for the question.

Can anyone think why the P0420 didn't show up until after I cleared the misfire code?

Second, is there anything meaningful in the attached readings of my o2 sensors?





Thanks for any help you can provide

 

PCM stoped testing when it found the intial problem. Once you fixed it, it starting testing again, and found the o2 sensor issue. Not an expert reading o2 waves. someone can jump in. Looks to me Downstream o2 sensor for bank 1 is not working. Also called switching. Note the longer lines on the others and not much change on that one. Its possiable just a bad 02 sensor.

 

I can't diagnose the charts either but it very well could be the sensor. I was getting a P0420 on my daughter's 4runner and thought it was worth the $60 it cost me to try changing the sensor before buying new CATs to the tune of $1500 to $2000. That was over 6 months ago and I haven't had any codes or CEL since. If you give it a shot - don't buy a Bosch sensor. Since then, my mother in law's Buick started throwing emissions codes. I changed her sensor several months ago and her problems are gone as well. Sometimes it's the sensor itself and not actually the problem that the sensor is reporting.

 

As others have said, O2 sensor issue. Simply replace it. Reset PCM and move on in life

 

I will give it a shot this weekend and update you on the results.

Thank you for the help.

 

well i had that code pop up this morning ,,,and for poops and giggles i removed my neg cable from the batery ,,,and the code went away ,,,,will it come back ?? if so will i have to change my sensors??

 

I got the sensor changed this weekend. I also took the negative battery terminal off to clear the code.

I believe if the sensor is truly faulty, the code will come back.

My has yet to come back.

 

Most likely. All you did was clear the code and nothing to address the problem itself. However, it may take a while before it comes back. See my response below for more info on that.

That code rarely comes right back. Those sensors have to complete a "drive cycle" before they will start throwing codes again. How long it takes depends on how you drive it and for how long. I have seen sensor specific drive cycles documented online where you can follow certain steps and force a completed drive cycle. The easiest thing to do, though, is just drive it as you normally would and see if it comes back.

When I picked up my daughter's used 4Runner, the CEL came on and threw that code within the first 20 miles on the way home. I stopped at an AutoZone and got it scanned and cleared and drove it another 200 miles or so before it came back on again. When I got it home, I cleared the code again and it took 3 days before it came back on. I cleared it once more (just to keep the wife from freaking out about my daughter driving with the CEL on) and it came back the next day. I changed the rear O2 sensor, cleared the code again. That was over 6 months ago and haven't hade a code since.

 

I was able to pull some new sensor traces this morning.

Old sensor:



New Sensor:


The suspect sensor is in red in both graphs

I think I found my culprit.

 

Makes you wonder how many people go buy new CATs just because a sensor went haywire. Then they find out after the fact that the sensor was bad and they wasted a lot of $$$.