-I don't think part number "3" is bad, because it is so much higher then fuel fill tube. Also it is "one-way-valve" and not ment to spill outside. Vapor can you can see in my thread and it is ment to return fuel back to tank.

-Check clamps top of tank, ones fitted to tank you can tight, rest of them is pressed.

-You should take out inner fender front "hatch" so you can see where it comes, it could be filler tube seal to tank. When you see this issue, be very carefull not to brake plastic that is aound fuel filler neck, it is very brittle.

 

,,,,be very carefull not to brake plastic that is aound fuel filler neck, it is very brittle.

what he said...

 

From the topsides with the carbon fiber cover off that reveals the top of the fuel tank and radiator tank, etc, I could see absolutely no signs of any past or present leak! It must be something under or along the drivers side firewall. I could see the entire fuel filling assembly from the inside and again no leaks. And after the initial small amount of fuel cleaned up by taking off panel 14, there has been no other drips sitting in the garage. I.e. it is not an active leak, it only appears to be residual from fueling. Everything else is bone dry.

If any of my comments jog the memories of the readers, I would appreciate your experiences.

 

Option there really is to fill up car while everything is visible on garage and see where it comes.
Small leak starts small and spreads as it goes down, not easy to see.
I would not drive car if it got fuel leak because those are where fires starts, right mixture of fuel and air.

 

They are pricey to buy NOS, so I rebuilt mine with wurth plastic bond and reinforced the back with fiberglass, will post shots tomorrow

 

Here is the damage to mine. I would love to see the back of yours to see what you did. I was thinking a strip of fiberglass in the back and lots of resin after bonding the cracks together. Also in the last pic, where is this hose going to? I cant find it in my Diablo wonder if it fell off.

Thanks
CCIE

 

I laminated it with glass fibre, it makes it stronger and keep rest of it splitting again.

https://www.lamborghini-talk.com/vbforum/1584802-post217.html

 

I think I’ll need to chase this gremlin by removing panel 17, the riveted one. (See my diagram above - panel 14 is to access the fuel pumps and has removable bolts for access). Has anyone done this? Is there any concern in doing so? Also, it’s unclear to me why there are two plugs in the panel 17, both small drain type plugs and not access points like a panel. Condensation drain? Water drain if rain wate collects?

 

There should not be anything behind that panel, unless you think someone have done something there or for some odd reason tank itself has leak, what it very unlike.

 

Thank you everyone. For future reference if anyone is in my situation, remove the passenger rear tire and fenders. They are attached with maybe 12 bolts 8mm and 10mm, very simple to remove. The photos attached are the view you will get with the rear passenger fender removed. It is significantly easier to access this location than from under the engine bonnet above.

 

Wow. That is one of the most useful and helpful posts in the history of automotive forums.

 

So, I removed Panel 17 under the car, the one with all the rivets. Photos attached. Also removed Panel 14, the one with the screws that accesses the fuel pumps and prefilters. Some evidence of prior leak around forward part of the gas tank. Filler tube and filters and tank all spotless.

I also removed the rear passenger tire, removed the rear fender, then put the tire back on, drove briefly down to the gas station -- fire extinguisher on the ready -- let the car cool, opened the bonnet, and fueled up fully. Nothing. No smell. No drips. So, back up the hill, cold start and cold engine with low RPMs to get home, then quickly shut the car down. Nothing. No smell. No drips. Onto something else for a few hours and came back to a very stinky garage - small puddle under where Panel 17 and 14 meet. Kitty litter in a pan collected the drips, and then started another 8 hours this weekend of sleuthing.

Followed the drip evidence upward to the top of the fuel gauge sender unit. Puddle! There is puddling fuel sitting on top of the indentation housing the sender unit, shown here. Match, anyone?!

 

Followed the drip evidence upward to the top of the fuel gauge sender unit. Puddle! There is puddling fuel sitting on top of the indentation housing the sender unit, shown here. Match, anyone?!

Another great day for German engineering and VDO... You need change that gasket, it is similar to other VDO gaskets, don't overtight it, tank is aluminium.

 

The top of the fuel tank in this location is accessed by the rear passenger fender with tire removed. You must have a six-jointed elbow, however. It is also accessed from the engine bay, past the CF shield, and naturally under the radiator tank and behind a frame member. For this, either have an 8-jointed wrist/hand combination, or simply remove the following 'ancillary' items: main fuel filters, power steering pressure system, vacuum tank and tubes, radiator tank and tubes having first drained the radiator of course, and remember to take many photos and label everything! Oh, and take the bonnet off -- mine is suspended here for easy storage

Good news is I found a random screw and the electrovalve for the bonnet is laying loose. All good: my winter project has begun!

 

Mikael, I had not even thought it was leaking upward from the VDO gauge gasket when fuel fill level is higher than that gasket. I thought it must have been dripping from fuels lines externally and pooling there. Great idea, thank you. Getting to that gasket may not be easy, given the many systems that need to be removed to get to it. Anyone know if this gasket work can be done with the tank in place in the car?

Mikael or anyone, "while I'm in there".... comes to mind. What other parts would you suggest I should replace while there? I see no other visible issues: vacuum lines look good, radiator hoses all look good, power steering hoses all look dry. Maybe the fuel filters, proactively? The whole VDO unit, too?

 

The whole VDO unit, too?

No, only rubber gasget under it, if it works, don't replace it.

You could LITTLE re-tight fuel line clamps, not much, just the slack. (ones with regular screw clamps, not pressed ones)

 

Good job. There's a price to pay for the beautiful lines of the Diablo, and that's working on them! I can't think of anything else needing attention there except I'd probably change the filters.

 

That hose drops straight down to drain out the vent slots in the bottom of the body panel below it. It is wire-tired to stay in place down there about 1/2 inch below the panel to drop gas onto the street. (Truly, it’s a water drain so rain water does not puddle and drip into the gas tank intake.)

 

@Diabloclyde I cannot answer on your PM. Something in your settings seems wrong.

Best,
Leo

 

Just changed my PM settings. Thanks for letting me know.

 

Ok, so I spent a few more hours on this. The radiator tank must be removed to access the fuel filters and the sender unit, but it is a huge PITA! It is darn near impossible to get out from outside of the car reaching over and back in under the body panel, so I had to carefully climb on top of the engine headers and access the radiator overflow tank from inside the engine compartment, (channeling my inner Sudesh!). At least on my 97, the radiator overflow tank has two large tubes coming into and out of a T on the inside of the overflow tank (see third photo), inside meeting closest to the street not closest to the engine. The removal of those two lines proved very difficult because there is just not enough room for human arms and the appropriate amount of leverage to pull the tubes off because the frame member as shown in the first photo prevents pulling the radiator overflow tank toward you to expose those lines. Keep in mind the radiator must be fully drained and you will still leak residual fluid all over the place. A side note: dog training pads with plastic on one side and highly absorbent cloth on the other side, the kind you will see in hospitals for patients that are bedridden, worked wonderfully in this application and in changing the fuel filters which I will get to next. Still, I could not get either radiator hose off of the T on the hidden side of the radiator tank so I had to actually cut the radiator line from the overflow tank back to the rear radiator. On re-installation I will install a union in an accessible location there, because if my fix of the gasket for some reason is not correct and gas still leaks, I will have to do this project all over again! It would be infinitely easier to have a union in the middle of that radiator line leading rearward from the overflow tank back to the radiators in case I ever have to pull that tank out again.

 

Once the radiator overflow tank was removed, I had easy access to the fuel filters. I ordered new OEM filters despite my relatively low miles because while I am in there .... The shop manual recommends replacement at if I recall correctly 45,000 miles but this is not a task you want to do again and the filters in this location are only around $80 per.

A word on the fuel filters. There is enough slack to pull the fuel filters aside and get to the sender unit with out needing to replace them, but it is very tight if you leave them in place. So I had to devise a way to disconnect the fuel line and filters and leave them disconnected for a time allowing me to get to the crux of the problem: the sender gasket.

I am an overly cautious neat freak and did not want vapors or liquid gas dripping un- collected, so again note the doggy training pads underneath. Worked like a charm. That said, I found some random rubber caps and plugs in my supplies and temporarily capped off the filters so as not to leak fluid or vapors shown in the 3rd photo. This allowed me to set them aside while I spend time on the sender unit which is doubly important with a family and kids and other distractions as they have been sitting in this picture for a week already!

 

I have now removed the radiator tank and upper fuel filters, replaced the fuel filters, and set them aside only to then be able to have a view of the top of the sender unit. All of this time I was worried the sender unit would not be able to be removed past the frame member visible in this photo. This was a nail biter: if there was not sufficient room for removal my entire fuel tank would need to be loosened and jockeyed enough to remove the sender unit or the tank would need to be taken out completely!

Thank God there was approximately 1 mm to spare. I forgot to attach a photo of the old fuel filters where I have temporarily blocked them from potentially leaking.

Now, when I got to this point it is a matter of loosening the five lock nuts being careful first to absorb any gas, clean any debris or liquids or sand or particles sitting in this indentation where the sender unit is. It would be bad to open the sender unit hole, pull the unit out and drop a screw, bolt, sand, bits of a gasket, or other material into the tank.

 

Regrettably, I forgot to take photos of the sender unit being removed as I tried to work fast. no matter how you drain your tank there will always be gas and vapors present that could ruin your whole day if sparked. I used a non-electric blower to blow the vapors out of the engine compartment, opened all of my garage doors, and insured plenty of air circulation. Battery is disconnected and electrical items in the garage are disconnected. Now is not the time to take up chain smoking either. The sender unit was perfectly fine. I could hear the float freely sliding up and down the tube when I moved it, therefore I did not feel the sender unit itself needed to be replaced. That said, I have never had troubles with my gauge level providing false readings. There seemed to be no damage or problem to the sender itself, other than needing the top cleaned that was exposed to the exterior of the tank. The gasket shown in this picture appears to have no visible breakage or failure, which gives me some concern when I put the car back together. What if it wasn’t the gasket? In that case, I will be taking this part of the car apart again to diagnose the problem a second time. For this reason, one must think of being able to get back into the radiator overflow tank and area of the fuel filters again. This is being taken into consideration as I re-assemble by adding an inline union in the above mentioned radiator hose and I will not fully tighten down the fuel filters’ housing. I did tighten the five locknuts down very carefully like you would Lugnuts on a tire with equal torque going to opposite nuts and progressing back-and-forth as you go. These appear to be brass screws and aluminum gas tank and you do not want to over tighten. As an abundance of caution per my normal routine I added anti-corrosive grease to the knots and threads.

Upon reassembly, I will take it to the gas station quickly after a cold start and refuel entirely. I hope I do not need to re-siphon 26 gallons of fuel into my other two cars! If upon full refill there is no gas leakage from the sender unit area, then I fixed the problem! I will report back.

 

Maybe fuel filter union was lose or sender gasket lost it tightnes.
You could fill tank up while everything is out from car.

Btw. easies place to drain coolant is from heater hose from lower radiator aluminium tube.
Also, it is worth noting coolant expansion tank is attached only from one end and it will only lift up from front side.

 

Not on my car. The tank has a tab that slides into a groove toward the passenger firewall while the easy bolt attachment is in rear of the tank. With no extra play in the radiator hose there was not enough wiggle
Room to remove the hoses by twisting the tank, pushing it aside, rolling it, etc just was not enough. Suggest anyone replacing radiator hose in this location to cut the new hose several inches longer than the hose coming out as just-enough is not enough.

 

On attaching the fuel filters and tightening down the bolts, I had two unions not want to seat properly. I carefully fired up the fuel pump by turning the key to its first position to ensure fuel pressure. And I saw drips. At this point I tightened the unions down further but I decided to add absorbent pad around each union to determine if any were leaking as seen in this picture.

Which leads me to another possible culprit: upon removal of the old fuel filters I found all four rubber O-rings, but only three of these thin metal washers shown (one is shown in my hand). these o-rings go on the metal fitting followed by their larger interior diameter washers such that when you tighten down the fuel filter the rubber expands into the inside of the washer to ensure a gas-right fitting. For some odd reason at the factory Luigi never added the fourth washer and that may have been my cause all along as I originally suspected. It likely worked just fine for these past 20 years without the washer but the O-ring started to fail and therefore leaked gas. This does not solve for the symptom of the gas leak only being noticed when the tank was full, but it could also have been leaking worse each time I turn the car on and therefore I only noticed recently. Keep in mind the fuel filters lie horizontally directly above the sender unit so any drip of leaking gas from this failing O-ring would have collected in the tank indentation for the sender unit. It’s either that or the sender unit gasket but at this point I may never know.

But amazingly I found a perfect fitting washer at my local parts store. In the Lamborghini parts manual the washer, O-ring and threaded union all are listed as one part, and I did not want to have to buy a new piece and wait for delivery.

 

For those of you contemplating doing the same work, absolutely replace the filters if you were to get into this area of the car as it is cumbersome enough to not want to do twice. I ordered new OEM filters which are Weber FI 02/2. As noted above, you will want to have 4 new O rings on hand which you can source at a local parts supplier. And you will want to have many absorbent towels, the ones I referenced that they use for puppy training or hospital uses work brilliantly.

That said, putting the car back together I need to ensure everything works perfectly before buttoning it all up. However I have to button the car up enough in order to make it run to the gas station to fill up the tank! So I reinstalled the radiator tank and added two inline unions, one each in the input and output tubes since they are behind the radiator tank and hard to get to. With these two unions and several inches of additional radiator hose in the lines, future removal of the expansion tank will be made much easier. This enables me to get the car to run again and test the new gasket on the sender unit to ensure it is no longer leaking and to ensure the fuel pumps are dry at their unions. If not, the entire expansion tank needs to come out again in order to get to the filters and sender unit. As they say, an ounce of prevention is worth a pound of cure.

 

there are two sets of 2 filters right? My upper filters (webers) were new, but the lower filters were very crusty and old. Did you replace both?

 

Good thing you found issue and notied possible leak source that is easy over look. There is fair amount pressure behind that and could cause fire, because sparkplugs are right next to it.

Filters might also be changed in some usual service, they are in "service program" and it could also be mistake made by mechanic later.

 

Yes, there are 2 upper filters as shown in my above posts and also the 2 pre-filters that come out of the tank before the fuel pumps. Given they are located next to a vented panel under the gas filler tube under the car, there is dirt and water access in this area and so at least the outward appearance you are experiencing is they are dirty. I'm actually replacing mine tonight or tomorrow because I have the fuel tank emptied and this would be an easier task now than in the future, though I expect residual fuel to spill from the hoses. I have pans with kitty litter on the ready! I am not touching the fuel pumps since both are just fine and I've had no issues.