164 fuel smell

[C M Smith <cmsmith@domain.elided>]

After several years of trying to track down fuel vapour smells in my 91 164 
we have traced the fault to the machine screws holding down the access 
cover for the fuel pump. As another digester has found, the fuel can 
migrate up the threads, presumably by capilliary action, without revealing 
any measurable pressure loss and without leaking any liquid fuel except by 
seepage. The resulting leak smells like a leak from the vapour recovery 
system, as it smells only of vapour, not of liquid fuel evaporating.

My fuel system was pressure tested with no loss of pressure and certainly 
the tank would hold significant pressure evidenced by that typical Alfa 
blow off every time you open the filler cap. The seepage only occurs when 
the tank is completely full, degenerating to the point where seepage occurs 
whenever the fuel in the tank sloshes around heavily (hard cornering or 
braking).

My mechanic was initially sceptical but pressurized the tank when 
absolutely full and left it for a few hours with the result that fuel 
seeped up the threads aggressively enough to show up as liquid drops.

It's fixed now, as far as we can tell.

If you get fuel smells in the trunk and you've fixed all those pesky fuel 
lines and clamps, check the top of the tank under the cover that hides the 
fuel pump access port. If the tank is full and under pressure you'll see 
and smell that seepage. Remove each machine screw one by one and seal with 
fuel resistant gasket sealer suitable for fuel lines, fuel pumps and 
similar applications.

Cheers


(wow, eh, useful technical info, not just ranting about SUV and US 
regulations) (exciting performance driving hints are now available from 
this source)
Michael Smith
White 1991 164L
Original owner
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