Diagnosing a Fuel Leak

Hi everyone, I the very proud new owner of a very used Tacoma. I topped off the fuel tank for the first time today and had an unsettling experience-- fuel leaking as it hit maximum capacity. There is zero leakage under any other circumstances. Can anyone suggest to me how I might troubleshoot where this leak is coming from, preferably without putting fuel all over my driveway? A visual inspection shows no obvious holes, but the fuel hose (between the inlet and tank) is decayed, sticky and mushy to the touch. No obvious holes though, and no fuel leaked until the tank was totally full, so I'm unsure if this is the culprit or a symptom. I'd imagine if it were the culprit fuel would leak during the entire filling process, which it did not.

Any tips would be MUCH appreciated! Thank you in advance.
Jon

 

How are you sure that it is leaking if there are no visible dripage?

 

if you see the fuel on the ground light it up and follow the fire



honestly replace those fuel lines first and see if that cures the problem, those lines are bad and its most likely the issue and if it isnt you needed to replace them anyways so keep looking

 

Surpa- fuel was definitely, visibly leaking as it hit full capacity when filling. It's just totally dry the rest of the time, and out of respect of the gas station dudes and for my wallet, I wasn't about to try putting more fuel in to see where it was leaking from.

BFA- That's good advice (the replace the hose part, not the spark it up part-- I think my days with the local fire department would come to an abrupt end if I tried that ). I'll start from there. Thanks!

 

let us know if it helps, then i would consider replacing all rubber components soon since its old enough to have rotten fuel lines

 

I'm having the same exact problem when I fill up my tank. I suspect the inlet hose as well. Mine is a 2005 model, I wonder if other 6 yr old models are having this problem?

 

IIRC, the filler neck is a hose held on by band clamps. Check the connections at the tank end and the filler neck end.

 

It's definitely possible that you could have a leak at one of the band clamps, but I wouldn't expect that unless the clamp has corroded so badly as to actually fail. Toyota designed the system very well-- there's a flange on both the tank end and the fill pipe end, little divots in the rubber pipe to mate with the flanges, and to top it all off the OEM clamps are the foolproof kind with a little nub to stop 'em when they hit proper tension, making it impossible to crush the pipe and pretty obvious if you under-tension it. And that fill pipe fits on there good-- I had to actually cut it off to get the old one out it was so snug on there. But certainly worth checking, if that is the problem you could fix your fuel leak with 30 seconds of wrenching.

As for my truck, I replaced the filler hose last weekend, and while it was in pretty sorry shape there were no obvious holes, so I don't think that I found the source of my leak yet. I haven't tried topping off the tank, but if it still leaks my next suspect will probably be the fuel pump gasket.

 

I can't see the top of the tank good right now, to verify, but from further reading with a similar problem, another possibility is the vaccum/vent hose. My inlet hose is fine so I suspect my vacuum canister or one of it's hoses. Will keep you posted.

Glad to hear toyota goes the extra mile on clamp hoses, thanks for the insight JonW

 

I hadn't even considered the vacuum/vent hose as the culprit, I'll check that out before I start wrangling with the fuel pump. Thanks for the idea!

 

Great Info here! and im currently looking at the EVAP section here: Good luck to us all!

 

I got some more gas in my gas jug and brought it home, to see where this fuel was leaking when the gas tank was full. I was previously just looking at the top of the tank from above the tire, up under the rear fender well. After filling the tank completely full, I could see gas puddling towards the front of the fuel pump lid, but the back area was dry. I of course checked the hoses and inlets first, and I can see all 3 of these, the main inlet, the canister inlet and return line on the left side close to the frame rail. They all have red cap pieces the hoses attach to. None of them were leaking, but there was a lot of fuel in the front of the fuel pump cap, lid thing...the big white gear looking thing in the close up pic.

I wanted a better look, and as i was crawling under the truck more toward the front, I noticed that I could actually see the top of the tank pretty good from between the cab and bed. I'm probably just slow and/or forgetful, but its a good vantage point, so I thought I'd share it and my findings today.

Also, I was thinking of the vacuum lines only because mine popped the P0441 Check Engine Light Code, but from what I've read elsewhere, it should be physically impossible for the vacuum lines to carry this much solid fuel.

Thus as the Great Detective Holmes stated, when you have alleviated all the probable causes, whatever is left, however improbable, must be the truth: Vis a Vis: There must be a problem with the tank or main fuel hoses themselves, causing the EVAP system to lose pressure and not complete the vacuum seal.

Thanks to JonW for mentioning the fuel pump gasket in the first place, looks like that's the culprit.

​

Looks like a huge job. I won't lie, I'm kinda scared of this one. I was able to pick up the Haynes manual for the 2nd gens yesterday.

But I don't know...anybody ever dropped the fuel tank before?

 

I have better quality photos I can email you if you want to try this yourself.

Toyota Dealer here in Jackson, TN quoted me 400 dollars for labor and said it would probably take 5 hrs. So, I'll prob be trying this one on my own.

 

Hey 7A7ER, have you tried dropping the tank yet? I'm a little wary of this job as well, I'd be very interested to hear how it goes for you.

 

Not yet. Gonna wait till I'm at my Uncle's garage, prob some time around the 4th, with multiple vehicles in case something needs to be went and bought, lol.

But it's definitely the fuel pump retainer ring, from the proper angle I can see where it is actually cracked and separating in the front area!

I'll let you know how it goes.

 

Allright, I finally got a chance to remove my fuel tank with the help of my very knowledgeable and very helpful Uncle. I tried to take as many pics as possible, but seem to miss getting any of the fuel tank being lowered by a small floor jack and thin 1x8 type board.

I have to say, the Haynes Manual was pretty spot on except for one small oversight. And funnily enough, the "quick" disconnects definitely took the most time. Especially the fuel pump/gauge electrical connector. More on that later.

I calculated the drive to my Uncles across the state, and rolled into his driveway after my fuel "Dummy" Light had been on for several miles. This only left a couple of gallons in my Fuel Tank and seemed very suitable enough for my experience. If you wish to siphon the tank completely dry that is of course an option and I leave that choice to you. I only lost a small amount of fuel through the fuel lines, just enough that you don't want it on the floor, so have a bucket or suitable container standing by for any over spill.

So lets get started shall we?

BEGIN BY PURGING ALL PRESSURE FROM YOUR FUEL SYSTEM

There are Three Steps:




(1) First remove the Gas Cap.



(2) Then disconnect the Fuel Pump Relay inside the Fuse/Relay box Under the Hood.

(3) Next Start your Engine and let it run until it dies. It may not start at all, but mine did crank up and run for just a few seconds then died just like the manual said.

NOW YOUR FUEL SYSTEM SHOULD BE PURGED OF ALL PRESSURE



Disconnect the Negative Terminal of your Battery

Now that the Fuel System is Purged and the Electrical System disconnected we can start removing the fuel tank.



Here is your gas tank rock guard cover. Behind it lies the gas tank...



It is held in place by only 4 nuts and is easily removed since it is lightweight but endurable plastic.



Here you can see the filler hose clamp screw through the cleverly placed access hole placed by the Toyota Engineers. Up and to the left you can also see the vacuum line quick disconnect, still embraced by it's yellow cover plate.



Loosen the Filler Hose Clamp by inserting your Phillips screw driver though this access hole.



Next unlike the instructions in the Haynes Manual, save yourself some time and go ahead and unsnap the yellow cover plate off of the vacuum line quick-disconnect BEFORE depressing the blue tabs and disconnecting the line with more force than you think would be necessary.



This is your Fuel Lines Quick Disconnects Cover Plate
Located just above and in front of your fuel tank.



Snap this off so you can get to the quick disconnect tabs.



Depress the Blue Tabs on each side of the lines and PULL



Leaving you with fuel lines like this. This is where I leaked good amount of Fuel. Have a bucket or suitable container ready to catch any fuel that runs out of the fuel lines. This seems to be the fuel that was trapped in the line forward of your tank, between the tank and the engine.

After this my Uncle was able to help, and things starting going fast. Before I realised it, the Tank was out and on the ground and I hadn't taking any more pics. I hope my words can paint a nice enough picture for ya...

Next we placed a small floor jack and about a 4 foot plank on top to support the fuel tank up against the bottom of the tank.

With slight pressure on the tank from the Jack, I disconnected the tank strap Pins by removing the retaining ring and hammering the pin out with a screwdriver and hammer. Then we removed the nut holding he strap on the other side. Repeat the process for the back strap and then the Tank is ready to lower slightly.

Lower the Tank slightly until you can get to the vacuum pump Quick Disconnect Line. This one was pretty stubborn, but keep at it and it will come off eventually.

Now Lower the Fuel tank just enough to get your hand over the top and get to the Electrical Connector. There is one Tab on the passenger side that only presses in with Great Effort and pressure. With only one hand, it was hard for me or my Uncle to press in enough to detent the tab and have any hand muscle/inertia left to force the connector up and off the pump. However, from the Driver's Side of the Tank My Uncle was able to somehow get it off. I know he had tried using a small screwdriver to assist him in applying pressure he may have used it the final time too.

Now you can lower the Gas Tank all the way down slowly while watching the fuel and vacuum lines for any snags.

Since its some sort of Plastic, the Tank is pretty light and manageable compared to other older tanks I have handled.

Slide the tank out from underneath the truck and begin removing the fuel pump retainer ring by disconnecting the fuel lines like so:




Remove these fuel lines by sliding/un-snapping the yellow holding clamps then pull up on the fuel lines to disconnect.

The blank hole is where the Electrical Connector that hangs on the frame of the truck was Disconnected.



My Retainer Ring was already cracked so we used a hammer and screwdriver to start to unloosen the ring. The little curly brackets are what keeps it from loosening and make it hard to take off. Just press in on the each curly tab as it approaches a stop and keep going around the ring and pressing in each tab in succession as you loosen the ring and eventually while one person presses down on the spring loaded pump the ring will unscrew the rest of the way off. (No Special Tool Required)

My Uncle held the pump down and in place once the Ring was off so that I could clean off all the dirt and debris from the top of the fuel pump, so no dirt or dust would fall into the tank once the pump was allowed to spring up.

Once it was relatively clean, we eased it up and replaced the fuel pump gasket while we were into it.



Then I replaced the Fuel Pump Retainer Ring with the New one.

Now the Haynes book says to stop turning the ring on, when the three lines on the cap are between two arrow markings on the tank. However after several tries, it was our experience that the retainer ring was too loose, since the fuel pump could still be pressed down and spring back up. We didn't want any more fuel leaks, so we kept going just enough until the fuel pump wouldn't spring up any more...which was turned out to be an extra half turn around. Hopefully this will prove OK. No leaks yet and everything operates as normal.



Reconnect the Fuel Lines and Yellow Retainers

Then we slid the Tank back under the truck and on the jack and board.

Everything was pretty much in reversal from here...jack it up enough to connect the Electrical connector and vacuum line to the vacuum pump. Then jack it into place by the markings on tank and frame.

Start the Tank Strap Nuts onto their bolts, just enough to hold them...this leaves enough play in your straps to slide the Pins in and complete with Retainer Ring. Once the strap pins are in, tighten the Strap Nuts all the way Tight.

Reconnect the Fuel Line quick connects and Reinstall Cover.

Connect filler vacuum line and yellow cover.

Connect Filler Hose and Tighten Clamp.

Replace Fuel Pump Relay

Reconnect Negative Battery Terminal

Reinstall Gas Cap

Crank Engine and MOC Fuel Tank by filling up and watching for leaks.

All in all it only took me and my Uncle about 6 hours. Hopefully you can have better luck and quicker time.

$70.00 dollars in parts and 6 Hrs of my time VS $400.00 dollars for the Dealership to do it.

I think I made the right choice. And you will too!

NOTE: According to the Haynes Manual there is supposed to be some big dark cover over the whole retainer ring/fuel lines/ and electrical connector to protect them. Mine was strangely missing. And given that the old retainer ring looked to be baked and one "spoke" was actually black as to have been burnt...I can only conclude that sunlight came through the space between the bed and cab just enough to "Bake" the front edge of the Fuel Pump Retainer Ring until it cracked in two. Look in between your drivers side cab and bed (Ext Cab Model at least) and make sure that Cover is there on top of your tank and that you CAN'T see your Retainer Ring. If your cover is missing too, this may be a problem, I can't say for sure, just my suspicion.

​

 

I have the exact same problem of the fuel tank leaking when I fill it right to the top. To remedy I have only been filling to about the 3/4 mark so Im not leaking fuel everywhere freaking the people at the gas station out.

Originally I thought it was the gasket between the filler neck and the tank as this looking like where the leak was coming from. I replaced this rubber gasket (and a broken gas tank strap) and it didn't fix it. PAIN in the ASS of a job dropping tank enough to remove filler neck. I couldnt remove the bolt on the top hose which goes to the fuel pump. So I just partially dropped the tank. Well the filler neck gasket wasnt the probelm. I figure there is a leak at that fuel pump gasket and the excess fuel is running down the top of the tank past the filler neck and then on to the ground, giving the illusion it is leaking at the filler neck just because you cannot see the top of the fuel tank.

To do this job again, I think I would just take the bed off.

 

Wow 7A7ER, thanks for posting such a detailed description of this operation with so many photos. This is all sorts of helpful to see as I prepare to do the same on my truck. Cheers!

 

I'm having the same problem with fuel leaking from the top of the tank.

 

Can you email me the haynes instructions on doing the job. Also would it be easie to just remove the bed instead of dropping the tank?