Intermittent Fuel Leak?

[ubster01]

Sunday evening as I was backing out of the drive I noticed a trail of fluid, I stopped and smelled it and immediately realized it was fuel. Fuel was dripping from the driver’s side rocker, exactly where the fuel filter is, I figured it was a hose as I replaced the filter about two years ago. I had my wife’s minivan exhaust torn apart and needed to get a clamp before the auto parts store closed, not wanting to be two cars down on a Sunday night I opted to drive to get the clamp and put some gas in my car so we could both get to work Monday. Maybe not the smartest choice but the weird thing is the leak stopped and hasn’t come back since I put ½ tank in three days ago.

When I parked it in the garage the Friday night before the fuel light was on so the tank was low from driving (still getting the 16.5 mpg average I always get), it was a hot weekend so I’m thinking the vapors expanded, maybe a vent isn’t venting and the system leaked at the weakest point at or near the fuel filter. When I backed out I think the trail of fuel was from it pooling / sitting on the cover. Again, it hasn’t been leaking since and I’ve been driving it to and from work this week (I have been venting the tank by opening the filler cap every morning and night). I think this has been happening in the past because I noticed a few "trails" down the drive over the last few months but assumed it was watery oil, remnants from my leaking valve cover gaskets.

I plan to check the hoses near the fuel filter tonight and replace as needed but am wondering if there is a vent I should check and how to check it. Also wondering if anyone else has had this problem and what they found. Thanks.

2001 540i 150,000 + miles

[geargrinder]

The tank vent system is a whole elaborate complicated sub-system as it is in all cars post-1980's for emissions mandated reasons. Typically called the 'evap' aka evaporative emissions system.

On any modern car for decades the tank vent goes via a 'charcoal canister' which is itself vented, but functions to trap the gas vapor from just going into the atmosphere. Originally you'd basically just have that vented to air, but from here they started adding stuffs over the years, and by the late 90's you've got a complicated system.

A vent from the canister typically runs to the motor via a "purge valve", so it can periodically suck on that canister and suck out gas vapors, purge valve opens for a while at startup and lets the motor suck on the canister for a bit.



In addition, the emissions regulators decided "BUT WHAT IF THE EVAP SYSTEM BREAKS!!!! WE BETTER TEST IT ALL THE TIME!"

So there are various ways the evap system is tested, in the later E39's by using a vacuum pump called "DMTL" (diagnostic module - tank leakage) which closes all the valves and sucks on the system to be sure everything is all sealed up. There's an earlier version of this called LDP, but it's not really that much different except for some minor technical differences.

http://workshop-manuals.com/bmw/5_se..._(dmtl)_all_u/

So... it's not common for the evap system to really crap out, the most common thing is the purge valve craps out and so it sucks gas vapors all the time and sometimes raw gas when the tank is full. But its possible your vent valve got borked or something I suppose but I'd be more likely to think your leak is/was really minor, and maybe there's some other factor going on. Maybe the hot weather is manifesting as inducing the rubber line to leak when its hot and soft. Maybe it's only "long parks' where the drips accumulate, and its' been leaking this week but you just drive it all the time and the few drips never add up before you drive off and they spray out and evaporate?

- - - Updated - - -

Oh and BTW, the DM-TL in theory should be testing your evap system all the time (OK not all the time, I think its something like "on every other cold start unless it's a Wednesday with a waxing gibbous moon" but still... happens regularly) , so you should have codes and an SES light if the system isn't sealed and/or isn't venting properly...

[ubster01]

Thank you geargrinder! I changed the hoses near the fuel filter and am pretty sure that took care of the problem. You were correct;

"Maybe it's only "long parks' where the drips accumulate, and its' been leaking this week but you just drive it all the time and the few drips never add up before you drive off and they spray out and evaporate?"

IMG_3311.jpg IMG_3312.JPG

I touched the rear worm clamp with my screwdriver and it started to drip!

It sat for a week while I was on vacation, no drips. Issue solved!