rdiggidy

I am wondering if the following would be consistent with a bad tank of gas:

I have had no problems at all with my 2001 4Runner w/ 140,000 miles on it (CA emissions) until a couple weeks ago.....While towing a small trailer (I don't think the trailer is related) the check engine light came on, which ended up being code P0420. I did some research and found this thread the most helpful: https://www.yotatech.com/forums/show...t=89187&page=3. I posted in there (last post), but got no response, so I posted here too: http://www.obd-codes.com/forums/view...hp?p=9022#9022

Just in the last day or two (I noticed yesterday) my check engine light has gone off and has stayed off all day today (at least 150 miles so far). So I?m wondering if I should just chock it up to bad gas and wait and see if it comes back on or if there is another symptom that could have caused this?

?Darkrooms? in this post http://www.obd-codes.com/forums/view...hp?p=9022#9022 says that it?s not possible for it to be my o2 sensor (which I just bought but haven?t installed yet), is that correct?

My game plan for now is to do a tune up (new plugs, wires, fuel filter, etc.) and then see if the light comes back on. If it doesn?t, I?m going to return the A/F sensor and o2 sensor I bought (to a tune of nearly $300) and assume it was a bad tank of gas (or some other phenomenon). And just keep hoping it's not my CATs $$$

Any thoughts or suggestions??

CyMoN

when it was cold out my o2 acted up if yours has never been replaced the you are past due anyway.
also my o2 seemed to kick the CEL every 200 miles then shut off then kick back on within 1 week

icerunner

YES and NO....What was the Code for?

Also, you probably only need to replace the 02 sensor "before" the catilitic converter as that sees most of the harmfull exhaust....Ive been told that the 02 sensor "after" the catty is good for far longer....
so replace the 1 st o2, and save your money on the 2nd o2....
also replace the o2 sensor nuts before they become perminatley rusted to the pipe, if you wait then you may have to cut the pipe off.
at least with chicago road salt

rdiggidy

The code is for "Catalyst System Efficiency Below Threshold (Bank 1)."

The full scoop can be found here:http://www.obd-codes.com/trouble_cod...old-bank-1.php or http://www.aa1car.com/library/p0420_dtc.htm

It seems that it normally means your CATS are bad, but they also suggest that it's possible that "Sometimes a faulty O2 sensor is not bad enough to set an O2 sensor code but is off just enough to affect the accuracy of the catalyst monitor"

That is kind of what I was hoping for as the CATS are expensive. But I don't understand how if either were bad it would just "fix itself" and the check engine light would go off....unless some other factor was causing the check engine light....such as the gas??

icerunner

You got it, I think it pretty rare forthe catty to go out at 140K?..... my 99 has 140K and I replaced the front oygen sensor. You're probably right as it may have been a bad tank of gas.... Where did/do you fill up? I stay away from the older gas stations as I have heard horror stories of rain water ending up in there larger gas holding tanks...
I would replace the before catty oygen sensor anyway
good luck

Beartracker

The A/F sensor should be replaced every 70,000 miles so you are way, way over due.I would be willing to bet that it will cure your problem, improve your gas mileage and you will see a gig difference in power and smoothness of operation. Very rarely will you hear of any water in gas problems from any gas stations. If you did you would hear about it from many people having the same problems and none of the stations want that kind of reputation. Mike

icerunner

You're a smart dude and I aggree with you mostly:
Years back there was a big news scandal that some independent gas stations were found to combining crude oil product to there fuel to save money. TO BE FAIR: I'm not totally sure what they combined with the gas with but it made your car run like crap. I'll need to do some research on that issue before I can talk with confidence on that.

As for the Rain water runoff: Mike, you are right it is rare or their reputation would be screwed.... My father would tell me all the time stay away from the older stations and never fill up when the filling truck was in the process of refilling the gas station tanks (due to debris/dirt being stirred up in the underground tanks)... and ending up in your car.

Now, I personally asked a "tank filler guy" at a BP station one day when I was filling my truck, and he said it not so much of an issue today (at least with BP) due to the fact that the gas stations filter the fuel now as it comes out of the underground tanks, before it is pumped into your car...
Call me paranoid, but I still will never fill up during or after the "tank filler guy" (for lack of the RIGHT job title)shows up at the gas station with the fuel truck... my thinking is , why risk it?

[B]as for water in the tank,[/B] I think it would be kind of a difficult thing to prove or figure out, I mean how many techs will do a "gasoline test" to check for water...?
Unfortunately rain water travels where it wants to and some of the older tanks do leak. If you don't believe me just ask the EPA how many underground fuel tanks eventually will leak andneed to be literally taken out of the ground and replaced. Actually its a big issue when it happens, as they ( the epa) have and commonly do hold the gas station responsible for the pricy ground cleanup $$$$.... AND Some times these gas stations can even contaminate an entire under ground natural water well/aquifer.....
i.e. this is the underground water that many people drink from, scary stuff
I'm not a genius on this topic and I thinkthat the newer underground tanks are better designed.
Yet, with ANY of the older underground tanks, the potential for leaks is there and if someone tells you that underground fuel tanks don't have the potential to leak, they are misinformed (or they are flat out lying).

CyMoN

gas and water do not mix water settles at the bottom.
also at gas stations these days they have water separators and filters.
I am very sure their pumps don't sit on the very bottom of the holding tanks as well.
same reason the fuel pump in our trucks sits up off the bottom of the tank and that there is a metal surround that keeps debris away from your pump.

Beartracker

Don't know how smart I am but I have been around awhile and it's very true that water was a common problem in your gas tank . Most of it came from condensation and some from the water in the gas stations tanks. I worked at a shell station when I was a kid and we Had to test the gas every now and then and it was not unusual to see tanks being replace due to water problems. You could even buy a product called "dry gas" at any auto parts store to ad to your gas tank when it started running rough.
For the most part that doesn't happen very often but that's not saying it never happens. Way to many filters on the gas tankers, the tanks and the pumps and I'm sure the refineries are much better than they were back then. That being said I use the cheapest gas I can find and have never had a problem with my 2.7. If you did some test you would find very little difference (Very cheap gas). Keep in mind that things like ads and fancy stations can drive the price up higher then the company who has a guy sitting in a little booth taking your money like the Duke stations do,Lol. Mike

CyMoN

easy to find out if there is water in the tank is drain it out into a 1 gallon pickle jar you will see real fast in the tank.

Beartracker

Good idea ! It would probably be a good idea for all of us to do that anyway with a few gallons of gas in it just to clean the tank out every few years. Well maybe not! I would just blow myself up as clumsy as I am, Mike