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Discussion Starter #1
OK everyone I feel very confident I have figured out how and why the 4.2s have so many problems with low MPG, constant O2 sensor codes and failed Catalytic Converters!
I'll get to how I came to this conclusion later on but I will just get to it...

With the second gen Rav4, Toyota wanted to make a model that the user didn't need to maintain until around 100k. For example, using iridium spark plugs and wait for it... a fuel sock instead of a proper inline fuel filter. The fuel sock is basically a mesh barrier in the fuel fill tube that is suppose to catch any large contaminates that may enter into the fuel fill tube. As you can imagine this is incredibly insufficient at catching all particulates. Once the particulates easily pass the fuel sock they then head for the fuel injectors. After time the injectors then become clogged and are unable to completely close during the normal opening and closing in the fuel cycle, thus becoming "leaky fuel injectors." The computer is unable to compensate for this as this is an electro-mechanical part.
Once the injectors are unable the close all the way, fuel then leaks out of the injector and creates a "fuel rich" environment. This is why MPG starts to go down because the computer is saying to the injector to close and not use fuel for that split second but the injector can't and "spills" fuel the cylinder isn't using.
Now the expelled gasses are fuel rich as they leave the cylinder since they have a much higher fuel content. Increased fuel makes for increased temperature which in turn "burns up" the O2 sensors and additionally the catalytic converter.

How do I know this? I know because once my CEL came on, I too replaced the stock Cat. with a cheap one off of Rock Auto and all 4 O2 sensors. MPG was still down to 17-21 but at least the CEL (check engine light) was off and I passed DEQ testing. BUT, it didn't take long, like 2 years, before the CEL was back on. After thinking about it for a long time I turned my attention to the injectors. I took our 2001 baby to Dr. Injector, here in Portland, and he confirmed that fuel socks do, in fact, allow particulates past and directly into the injectors. He discovered that 2 injectors were completely done and the other two could probably be cleaned and used again. I opted to replace all four with genuine Toyota injectors for a grand total of $675.00. After that I then went to the dealer an bought a Toyota Catalytic Converter for $775! This one went in much easier after having replace the first one myself.
Just after all the work we took a road trip with my wife and I in the front and my two in-laws and our son in the back row. And what do you know I got 27 MPG!!!! Which is what we were getting when we first purchased the vehicle used, back in 2005.
I hope this helps!
Please let me know if you have any questions.
 

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Discussion Starter #3
I have not. My Dad has a 2001 4.2 and lives in Colorado. His tags are due to expire and he will then need to pass environmental testing.
His CEL is on and will do the exact same fix that I went through. At that time he is planning on putting in an inline fuel filter. I'm just waiting to see what he finds out.
If I wasn't moving abroad soon and selling our 4.2, I would have had the injectors cleaned and then installed a high pressure inline fuel filter in order to save the injectors and not have to have the injectors cleaned again.
 

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I have a 2003 Rav4 and it is fitted with an in tank filter as shown in the photos. Does yours not have one like it or are you saying that this filter is not adequate?
 

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Discussion Starter #5
Correct. As a non-serviceable part the "filter" is unable to capture the small particles that eventually clog the injectors.
The proper fix would be to install an inline high pressure fuel filter in the engine bay.
 

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Hi 2001Rav4, have you been replacing your in tank filter? I change mine every 80,000km. My Rav has done 160,000kms and I'm about to replace the one I installed at 80,000kms. How many kms/miles has yours done? What would be the difference between an in tank filter and an inline filter?
 
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