A Gas Cap Question

[tenro1]

Back when I first bought my T4R (2001 - 2wd 6 cyl) I got the P0420 code, and found the gas cap was not tightening properly. I replaced it with a gas cap from Autozone. The one they had listed in the computer did not fit at all, the guy behind the counter said they had to go up a year to the 2002 model to get the correct fit.

So, I installed it, and it fit where I could tighten it down. This was back in December 2013.

Ever since then, when I stop to buy gas, I have a real hard time getting this cap off - like I have to take 2 hands and really turn to get it off. But when I put it back on, I turn it, and then it clicks 2-3 times...but it even takes a bit of turning to get it to do that.

The other concern I have realized is that, when I do take the cap off, I hear no hissing sound of releasing pressure in the tank...doesn't matter how much fuel has been used...I never hear that sound.

Lately, I have begun smelling gas intermittently inside the vehicle when driving...cold or warm days, cold or warm vehicle. I have checked all the locations to check...fuel filter, fuel injector rails, fuel pump seal by sniffing around and under the rear seats, etc...cannot detect anything...The smell is not constant, but, can get a bit strong at times.

It's making me wonder if this gas cap I got is not the right fit for the vehicle...and yeah, by the way, still getting the P0420 codes as well...

Thoughts....????

 

[Blitzkrieg]

This happened to my 2002. I replaced the gas cap with a Toyota factory replacement but it would occasionally throw the code which is the fuel system evaporative system or similar.

I spent hours going through everything and (which does not happen very often) I was at a loss.

I took it into my Toyota dealer and after 1.5 hours of diagnostics they found the root cause - my plastic charcoal canister had a small crack in it.

The tech said he had seen it happen a couple of times and I guess the canister is a real PITA to get to. I don't remember what the tab was exactly but I seem to recall like $300.

Also if your evaporative system is functioning correctly you will not hear any hissing or whooshing when you open the cap. The fact that your cap takes two hands to remove tells me the system is failing and your tank is vacuum locking the cap.

 

[tenro1]

Thanks....

I am not getting the codes for the evap system...my code is P0420, catalytic converter below threshold error. And, as far as the cap goes, I went out just now and took off the gas cap, (no woosh), and then put it back on with exactly 3 clicks...then turned it off again...this time, it was not so hard to take off. So, I started the truck and drove around for about 10 mins to build up pressure in the fuel system...came back home, and took the cap off again...this time, it was a bit harder to take off.

So, I am thinking you might have something regarding the vacuum aspect. But here's the thing: I looked at the gas cap after reading your comment, the cap is a Slant cap, and below the trademark, it says "Vacuum Only".

So - if you are saying that a vacuum should not be building up behind the cap, then why does this cap say this? Is this an incorrect cap?

BTW - while I was doing that little test drive, the good old P0420 came back on...yeah....lol

 

[tenro1]

So, I guess my question at the moment is: Should the gas cap be of the vacuum design, or the vented design? I see the one I bought at Advance (not autozone) was the Stant/vacuum only design, and the one they sell at Autozone is the CST cap, which is of the vented design, not vacuum.

Which one is correct?

 

[Blitzkrieg]

I believe the Toyota factory cap is a vacuum unit as the EVAP is a sealed system.

Check this out:

P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1)

You need to start looking at your O2 sensors IMO. I am assuming this vehicle never had leaded gas run through it (or do we not know)?

I got sidetracked by your "cap not fitting" and was not paying enough attention to your actual OBD error code. I have the one mine was throwing recorded on the invoice to get it fixed and will try to find it, but it was not the downstream cat/02 you are seeing.

And what I meant by vacuum locking was not a failure of your cap, but a failure elsewhere in the evap system. The pressure from the gas in your tank expanding should vent to the charcoal canister and equalize things out more/less.

 

[tenro1]

O2 downstream sensor was replaced in January...still getting the code. So...why would one parts store sell a vacuum only cap, and the other sell a vented cap, no vacuum design according to the specs? This is a bit confusing...anyone else running the Stant vacuum only design (part #10834) on their 3rd gen?