tank venting system, major leak error code: HELP!

[Ryan Turner]

I have a 97 BMW Z3 2.8 with 260,000 miles (yeah, I know). There is a problem that may finally total this car, as I dont know if I am going to spend the money it may require to have it fixed.

There is a check engine light on indicating a "tank venting system, major leak." My very good mechanic has done a lot of things to look for the leak so far. He has replaced the purge valve and we have purchased a new fuel cap as well as new seals for the old one. We cannot get the error code to clear. It looks like the next step is going to be to drop the entire tank, and that is a major deal.

Has anyone else run into this problem?

[lpcapital]

I'm not sure how that is diagnosed in the older car like yours (newer car actually have a separate pump which pressurizes the tank an measure the decline in pressure): I'll try to look around in my literature...

I know the DIS (the official BMW diagnostic platform) has a very through diagnostic procedure when it comes to fuel thank leaks that help you narrow down to the source of it; I suspect your mechanic is an Indy who just uses a general code reader...

In some pictures I once saw somewhere some of the epoxy used to seal some of the sheet metals around the fuel thank was exposed and rubbed against the fuel thank. In that specific instance you could only notice a minor dent in the thank... But as time would have gone by it would have probably ended up causing a rupture in the fuel thank...

The only suggestion I have right now is to fill up the fuel thank ALL the way while on a lift and see if you find a leak...
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2003 Z4 2.5i
2002 Ducati Monster S4

[Ryan Turner]

Thank you for the reply. The shop is an indy, but they only handle BMWs and have an expensive code reader. My mechanic is awesome, but as he states, they only get a small representation of all the problems out there since they are a small shop compared to the dealer.

One thing I have noticed, is that regardless of fill level, after you get done driving and look at the seal around the gas cap, it is always wet with gas. I figure gas sloshed up there, and that is to be expected, but if any of you wouldnt mind confirming yours is wet or not, I would appreciate it.

[lpcapital]

Fuel is not supposed to escape...

Try this.

If you have an old tire tube laying around cut out a disk so that it fits tight on the fuel cap. The gasket might have dried and shrunk over time.
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2003 Z4 2.5i
2002 Ducati Monster S4

[Ryan Turner]

Well, thats the problem. We have done the following:

1) Purchased a new gas cap (after market).
2) Doubled up after market seal (can barely turn it because it is so snug)
3) Took OEM seal and fit it on existing OEM cap.

In all three of those instances, you can still see gas on the seal.

What would be an 'idea' jimmy rig to rule this out once and for all?

[Ryan Turner]

Oh, and in all three instances, we reset the check engine light and waiting to see if it would clear inspection mode.

I dont care if I need to duct tape the damned thing shut to see if the check engine light will clear. At this point I want to pinpoint the problem.

[lpcapital]

...previous post. So you did replaced the seal already.

Here's the diagram of your fuel thank: http://www.realoem.com/bmw/showparts...05&hg=16&fg=05

As you can see there's a lot of stuff around it, but none of them is accessible without dropping the fuel thank.

It could be an actual leak or it could be the sensor being faulty.

I can't help you much more: of all the problems that Z3 normally have, the fuel thank is not in my top 10, so I can't help much... Maybe someone else has some first hand experience with this, otherwise it's just guesswork...
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2003 Z4 2.5i
2002 Ducati Monster S4

[lpcapital]

If you look behind the passenger seat, there's a perforated section of the carpet. If you complete the pre-cut you'll be able to flap it open and access the fuel pump. Maybe (and I say maybe) you'll be able to find something behind it, like a leaky fuel pump gasket or vent hose or something...
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2003 Z4 2.5i
2002 Ducati Monster S4

[Ryan Turner]

Yeah, we've done that too. A few times over the past couple of years, there has been gas fumes in the car, normally after a fill up, to the point where I took it in.

I think I am going to fill the car with as much fuel as I can, park it on my very steep driveway (30 degrees) and see if fuel comes out of the filler cap.

I assume if it does, it should not?

I may have to bite the bullet and buy a new locking cap, as the non OEM may not have been a good replacement.

[lpcapital]

I would start by buying the OEM seal only... No eBay, not cheap... Just go to the dealer...
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2003 Z4 2.5i
2002 Ducati Monster S4

[@ bimmer2.8]

i replaced my original locking cap many years ago with a non locking BMW one....worked great and back then it was only 10 bucks for the cap...probably more now.

[SteveJ]

I just went through this with a gas cap that wasn't properly tight. First of all, you will need to drive the car a couple of days through a couple of engine start cycles to see if any fix works and the light goes off. The next step would be to get a new OEM gas cap from the dealer to see if that fixes the problem. You should not see any gas on the rim when you carefully remove the cap.

[Unregistered]

Does anyone know where I can find an oem locking gas cap for 1997 BMW z3 2.8 roadster at a reasonable price?
I cannot seem to find one on the internet anywhere.

[rhturner]

No. There is no place to get them reasonably. Your best bet is the dealership, and its going to set you back around $100. You'll need to bring your license and registration.