The Impossible Fuel Vapor Leak (Page 1/1)
James_GT JAN 19, 07:05 AM
Hey all, hate to admit it, but my '87 GT has been giving me grief since winter last year.
After spending a few hours working beside it in my enclosed garage, I felt very unwell. Turns out it had been leaking fuel vapour, particularly in the area ahead of the rear-right wheel.

I started searched for liquid fuel leaks, and found one at the block-to-rail seal. Replaced the seal thinking that would've been it, but wasn't so lucky!

Checked my braided fuel lines, injector seals, CSI-delete bolt, pressure regulator, hard and rubber lines leading to the expansion tank and charcoal canister.
Removed the wheel well liners and attempted to detect vapour in those areas, couldn't notice it there either.

I ended up taking it to two separate mechanics. First shop dropped the tank, and weren't able to locate any leaks. I thought they would find something around the fuel pump gasket, as I had replaced the FP the year before. Instead I was told I did everything right, and it was all sealed correctly. Which wasn't what I wanted to hear!
It was difficult convincing them the vapour leak even existed, because it's a lot more effective at dissipating in a large workshop environment.

Second shop also dropped the tank, and found the rubber filler hoses had grooves worn into them. They had custom replacements made up, and were confident the problem was solved. I would've thought so too, but again, it continues to vent fumes from somewhere else.





Some days it's barely noticeable, but on others it's quite strong. I can usually pick up on it as I approach the driver's door (my Fiero is right-hand-drive converted).
Seems like the leak could also be affected by ambient temperature.

Yesterday I got stuck into narrowing it down. Following my nose, while using a cardboard insert from a roll of paper towels.

Here's a summary of what I've found:

- Vapour is at its strongest in the cavity at the rear of the fuel tank

- Vapour vents up through the engine bay and beside the right-rear quarter panel

- No noticeable vapour in wheel wells, fuel cap area, or where expansion tank and filler tube are housed

- No liquid fuel leaks

- Replacement fuel filler vent hose has kinked

Anyway, that's about all I can say about this. If anyone has had a similar experience or can recommend any tips on how to solve it, I'd really appreciate it!

------------------
James
RHD '87 Fiero GT

[This message has been edited by James_GT (edited 01-19-2020).]

fieroguru JAN 19, 09:35 AM
87 and 88s have an expansion tank for the gas tank vent line mounted right by the battery, on the other side of the chassis sheet metal and bolts to the upper frame rail along the outside of the chassis.

You can see the backside of this tank through some of the holes in the sheet metal if you remove the battery and pull back the insulation

They have been known to clog and leak due to rust.
fieroguru JAN 19, 09:42 AM
The other thing to check would be the braided stainless lines. If they were made from normal rubber fuel line, they have been known to start venting fumes as the rubber breaks down. Some have eventually burst with age and have caused engine fires.

I only use ptfe braided stainless steel for this reason.
Gall757 JAN 19, 10:27 AM
The expansion tank is connected to the fuel tank via metal lines that are visible by removing the battery. Battery acid can eat those lines.
You are right.....the smell would be affected by ambient temperature....Temp goes up.....fumes are pushed out.
Make sure you have a vacuum on the canister....and that the charcoal is not ruined by liquid fuel getting to it in the past.

[This message has been edited by Gall757 (edited 01-19-2020).]

theogre JAN 19, 02:39 PM
Auto Drop Tank is wrong thing to do.
Smoke test would help find many EVAP leaks and vac lines problems.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

James_GT JAN 19, 07:39 PM
Thanks everyone for the info, I have been looking into the expansion tank as a possible cause.
I ruled it out, on the basis I couldn't smell vapour in the wheel well where it's housed.



The hard lines on the other hand, could very well be the source.
Batteries have leaked and caused mild corrosion on the tray, but only enough to strip back some of the paint.

Expansion tank lines running along the firewall appear to be in good condition.

However, the line in the photo below looks a bit concerning. Can't imagine it should be bubbling up like that.
If it is leaking vapour there, is it as simple as applying JB weld to the line to repair it?



The braided fuel lines are from The Fiero Store. As far as I know, they're made from stainless and were only installed a couple of years ago.

Will test for vacuum. If the charcoal were ruined, would it be venting strong fumes directly out of the canister itself?

I agree about the smoke test. Unfortunately, I had a hard time finding a shop with the right equipment.
The second shop I went to claimed they borrowed a smoke machine, but didn't get any results. Maybe they're not as widely used here, as we don't have regular emissions testing in Australia.

One correction I should make is regarding the filler hoses. Looks like they're actually meant to have those grooves (see photo in my original post), which were not just a case of wear and tear.
Factory replacements from TFS are moulded into each other when they're produced.

[This message has been edited by James_GT (edited 01-19-2020).]

Patrick JAN 19, 08:08 PM

quote
Originally posted by Gall757:

The expansion tank is connected to the fuel tank via metal lines that are visible by removing the battery. Battery acid can eat those lines.



Bingo! I have that problem with my Formula. Small pinholes in one of the metal lines, caused by battery acid at some point years ago.
theogre JAN 19, 09:29 PM
Yes, Battery "Leaking" can eat them months to years later... Also the Brake(s) too.
So if any/all fuel lines show damage check brake lines and "T" block as well.

87 88, maybe some earlier, Fuel supply and return lines runs under battery too so check both w/ engine running first.
Return line leaking can weep and not be obvious because that line has little or no pressure.
James_GT FEB 14, 06:58 PM
Quick follow up. I had a closer look at the exp. tank lines underneath the battery, found mild corrosion.



As a band-aid fix, I sprayed the area with WD-40, let it dry, then wrapped the line with black HVAC caulk.
Had quite a bit left over from when I replaced the heater core. JB weld may be better, but this was easier to apply in a confined space.



Sealing this seems to have helped, though I'll still occasionally notice the vapour odour. Doesn't appear to be anywhere near as strong as before.
The workshop will replace the rubber filler hoses (including the kinked vent hose) under warranty. While they have the tank out, I'll be sure to double it's sealed properly.
creaky78 FEB 18, 03:39 PM
Had the same problem, steel lines under the battery tray rusted through. Never did smell any fuel vapor, not sure why not. Anyway, I cut the rusted portions of the lines off at a point between the frame and engine where the lines were still in good condition. Removed the old rubber connection lines from the tank and ran new rubber lines to where I had cut the steel lines off.