gwgeep

I noticed recently that I smell gas fumes when I completely fill the rear tank. Normally, I usually use the front tank and keep about a 1/2 tank in the rear for spare and then cycle thru it and put in another 1/2 tank. But recently I decided to use the rear tank more often and use the front less. But, I noticed the smell of fumes when I did this. The engine runs fine on both tanks and even replaced both fuel caps since the 24 year old fuel caps rubber was all but gone. So, I just wonder if there is something about the rear tank that I should investigate. Recently turned 170000 miles and drive it every day and shined it up last nite.

Chris_1

iTrader: (1)

There is a vent line that goes from the tanks up to the charcoal filter under the battery. That's a possibility. Or a leak at the top of the tank that could be a few things from a gasket to a hole.

gwgeep

You can guess what I will be doing soon...like crawling all over, under, in/out engine compartment and tween here and there to figure it out....

Steve83

Get an inspection mirror, and a flashlight that focuses. If you need to access the top of a tank, I find it easier to lift the bed than to drop the tank (especially if the tank is full). Read this & the NEXT few captions:


(phone app link)

For more about the tanks, read all the captions in this album:


(phone app link)

gwgeep

Well, I have been using the rear tank with the front tank full. Came home today and smelled gas around the truck. Looked underneath and saw some fuel on the ground under the front tank. It seems to be leaking from the top of the front tank at this point. I will give it a looksee tomorrow and use a lighter to give me some light...

gwgeep

I investigated the EVAP system and cleaned out the EVAP Charcoal Canister and checked all of those lines. The canister definitely was getting vapors by the smell of the air coming out while blowing air thru it. I did a vacuum check on the "Fuel Vapor Canister Purge Regulator Valve" and it held so the valve is okay. I then did a check on the valve they the hose to the Throttle Body and there was a leak in the hose. Old, brittle, hard hose was not sealing very well, so I replaced it with new vacuum hose and that problem was corrected. IF THERE IS UNREGULATED AIR FLOW INTO THE THROTTLE BODY THEN THAT CAUSES IRREGULAR ROUGH IDLE. So, I will watch that portion of the RPM's to see if the idle stabilizes.

I checked on top of the front fuel tank for a leak, but did not "see" one with camera and light. It is very possible that when I overfill the tanks, the top vapor valve might leak, but do not know for sure. But, as I use fuel from both tanks, and reduce the fuel levels, I do not get an overdose of fuel smell. I will keep a "nose" out for the fuel smell for the moment, but both fuel pumps work fine in either fuel tank.

Chris_1

iTrader: (1)

You may be getting some cross filling. If one of the check valves is faulty the when you're using the other tank it pumps fuel into the tank with the faulty check valve, causing it to overfill.
It's another possibility; keep a close eye on the amount of fuel in each tank to see if maybe one is filling up while you're using the other one. If you follow that.

Shagg

Steve83

Yes, it just happens a different way:


(phone app link)

gwgeep

I have been taking time in inspecting the EVAP system in relation to my fuel smell issue. I cleaned out the charcoal canister and made sure all hoses to/from the canister to the Purge Valve are good and tight. I found one vacuum line going to the throttle body was not tightly sealed. It was old and hard rubber. I tried to hold a vacuum thru the hose back to the Valve and it did not hold, so I replaced it. Then I took off the valve and held a vacuum directly on the output of the valve and applied 12V and the valve opened up and the vacuum was released. I checked the Voltage running to the valve connector and the V was always 12V. I then tried to hold a vacuum on the input side of the Valve - the side that is fed from the charcoal canister. This side does not hold a vacuum. Should the input side that is from the charcoal canister hold a vacuum as well as the output to the throttle body on the purge valve? So, just to summarize if I may, output side of purge valve holds vacuum, but input side of purge valve does not. Is this correct or should both sides hold a vacuum when testing?