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Discussion Starter #1 (Edited)
My 2002 Rav4 is running lean. The Long term Fuel Trim on Bank 1 at idle hovers around 14 to 16% and on Bank 2 around 3 to 7%. While accelerating both LTFT are increasing and while driving at highway speeds around 60-70m/h the LTFT on Bank 1 stays at 19.5% and on Bank 2 stays at 13%.



I've kind of excluded the possibility of vacuum leak at which the LTFT would actually be decreasing while accelerating instead of rising. Possible causes could be either a dirty MAF sensor, weak fuel pump or maybe some other fuel delivery problems? Few other things are happening with the car as well; 1] car stalls for just a second at stop light or intersection from time to time very randomly tho. 2] also this only happened few times that the car's idle got very low at stop at around 300-400 rpm. Car started shaking, with rough idle but as soon as gave some gas it drove ok.
Little history, year ego, I got a P0420 code and had my Cat replaced. Last month I got the same code again plus P0430 and had the same CAT replaced under warranty. Now I am thinking that maybe the fact that the car has been running lean all this time caused the CAT to go bad twice on me. Since there are no codes, no mechanic ever bothered to look into the reason for the CAT going bad. Where should I start to look? Whats the most possible cause for the engine to run lean? How do I change the fuel filter or replace the fuel pump myself? Are there any other tests I could run to zero down on the problem? I am looking forward to any suggestions... Thanks
 

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"no mechanic ever bothered to look into the reason for the CAT going bad."


Why Catalytic Converters Fail

mine is currently throwing a code telling me the converter is bad, I believe my problem stems from a head gasket repair, removing those rusty exhaust system bolts and nuts I may have contaminated it, but that doesn't sound like it would be your problem.

a bad O2 sensor can cause a cat to go bad, either adjusting the mixture too rich or lean, I don't think that was my problem, my problems started just after doing the head repair, no codes before the repair, just a loss of coolant, also I had used brake sytem cleaner to clean the threads in the head, that's nasty stuff, with all the chemicals I used, and my liberal use of them (vehicle had 180,000 miles) and the code coming on shortly shortly after the repair (I think a couple days) I'm pretty sure that's what did my cat in

BTW, too lean causes the temp in cylinder to go up, but in the cat isn't it a too rich mixture which causes the overheating ?
 

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Discussion Starter #3
"BTW, too lean causes the temp in cylinder to go up, but in the cat isn't it a too rich mixture which causes the overheating ?"

From what I read, both, running rich or lean can make the CAT go bad if it's happening for long enough. I would suggest for you to check the Fuel Trim on your car as It may be also running out of range. For my case, I suspect either a MAF sensor went bad (ordered a new one as it cleaning did not help) or some kind of fuel delivery restriction. With 205K few things maybe old and in need of replacement, fuel injectors, fuel pump and filter, or even the fuel regulator (unfortunately the last 3 are located in the fuel tank :()? I am not sure how to check all of this especially in the beginning of Chicago Winter. My hope is that some Rav4 owners on this forum maybe went through a similar problems with their cars and could maybe steer me to what to do next?
 

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shouldn't the wrong fuel trim or anything else which changes the air/fuel ratio affect gas mileage? and possibly power?

I have kept track of mine for 201,000 miles, since new, in summer it gets 29-31 like always, and now gets 25-28 like it always has in the cold and that they changed over to winter gas

I know what you mean about working on them in winter, MN winter here :)
 

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Discussion Starter #5
shouldn't the wrong fuel trim or anything else which changes the air/fuel ratio affect gas mileage? and possibly power?

I have kept track of mine for 201,000 miles, since new, in summer it gets 29-31 like always, and now gets 25-28 like it always has in the cold and that they changed over to winter gas

I know what you mean about working on them in winter, MN winter here :)
Yes, the fuel trim does effect the gas milage. In my case the car runs lean at 19.5% so theoretically I am using almost 20% more gas then the car should. The Torque App I'm using shows only 22-23 M/Gal in the winter and mainly on the Highway (City driving would be even worst). Summer I am not sure as my wife drives this car normally. Today I am getting my own Fuel Pressure Kit from Harbor Freight ($11.99 on sale now) and will finally find out if I may have problem with the fuel pressure in the system. Before that I will try a new MAF sensor in case its that as cleaning the old one did not result in any improvement.
 
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